UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Comparison of spatial contrast sensitivity between younger and older observers Dahl, Howard Stewart 1985

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1985_A8 D33.pdf [ 5.07MB ]
Metadata
JSON: 831-1.0096489.json
JSON-LD: 831-1.0096489-ld.json
RDF/XML (Pretty): 831-1.0096489-rdf.xml
RDF/JSON: 831-1.0096489-rdf.json
Turtle: 831-1.0096489-turtle.txt
N-Triples: 831-1.0096489-rdf-ntriples.txt
Original Record: 831-1.0096489-source.json
Full Text
831-1.0096489-fulltext.txt
Citation
831-1.0096489.ris

Full Text

COMPARISON OF SPATIAL CONTRAST SENSITIVITY BETWEEN YOUNGER AND OLDER OBSERVERS by HOWARD STEWART DAHL B.A. University of British Columbia, 1981 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in THE FACULTY OF GRADUATE STUDIES Department of Psychology We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA July 1985 HOWARD STEWART DAHL, 1985 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the head of my department or by h i s or her representatives. I t i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. The University of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 D a t e / I f o . Department of / s y r i i A b s t r a c t Contrast s e n s i t i v i t y to v e r t i c a l l y o r i e n t e d g r a t i n g p a t t e r n s with a s i n u s o i d a l luminance p r o f i l e were examined between groups of observers v a r y i n g e i t h e r i n gender or age. For each observer at each of the seven s p a t i a l f r e q u e n c i e s t e s t e d (.75, 1.5, 3, 6, 7.5, 10, 15 cyc/deg) t h r e s h o l d v a l u e s were c a l c u l a t e d f o r e i t h e r ascending or descending t r i a l s as w e l l as a combination of both. These t h r e s h o l d values were n u m e r i c a l l y transformed i n t o s e n s i t i v i t y v a l u e s and c o n t r i b u t e d to a group mean c o n t r a s t s e n s i t i v i t y score f o r each s p a t i a l frequency. No s i g n i f i c a n t e f f e c t of gender was found but younger observers (mean age=22.6 y r s . ) e x h i b i t e d s i g n i f i c a n t l y b e t t e r c o n t r a s t s e n s i t i v i t y than the olde r aged group (mean age=66.2 y r s . ) f o r ascending t r i a l s at 3, 1.5 and .75 cyc/deg--the lowest s p a t i a l f r e q u e n c i e s t e s t e d . Contrast s e n s i t i v i t y was a l s o c o r r e l a t e d with v a r i o u s measures. These f i n d i n g s were d i s c u s s e d i n r e l a t i o n to the e x i s t i n g l i t e r a t u r e on age and s p a t i a l c o n t r a s t s e n s i t i v i t y and s i n c e the machine used to examine the c o n t r a s t s e n s i t i v i t y f u n c t i o n (CSF) in t h i s study u t i l i z e d a l a s e r i n t e r f e r o m e t r i c method of stim u l u s g e n e r a t i o n , p o s s i b l e n e u r o l o g i c a l changes with aging to e x p l a i n t h i s noted l o s s were a l s o c o n s i d e r e d . A l s o d i s c u s s e d were v a r i o u s parameters that e f f e c t the CSF with a view toward e x p l a i n i n g the d i s p a r a t e f i n d i n g s of v a r i o u s e x i s t i n g s t u d i e s of age and the CSF. i i i Table of Contents Page L i s t of Tables v L i s t of F i g u r e s v i Acknowledgements v i i i I n t r o d u c t i o n 1 V a r i a b l e s E f f e c t i n g the Contrast S e n s i t i v i t y Function 19 Ocular Pathology 19 Gender 23 Response Bias 25 Monocular versus B i n o c u l a r viewing 26 P u p i l S i z e 26 R e f r a c t i v e State of Eye 27 L o c a t i o n on Retina 28 Sine wave versus Square wave 33 Temporal Modulation and Shape of Temporal Envelope 33 G r a t i n g O r i e n t a t i o n 35 Presence of Edges i n the Stimulus F i e l d 37 Target S i z e or Number of Pe r i o d s i n the Stimulus F i e l d 40 Mean Luminance of Pa t t e r n 43 Luminance of Background 46 Colour of P a t t e r n 47 Method of Determining Threshold . 48 Age of Observer 53 Method 65 Sub j e c t s 65 Procedure 65 R e s u l t s 69 D i s c u s s i o n 88 References 98 Appendix One P h y s i o l o g i c a l / A n a t o m i c a l C o n t r i b u t i o n to Understanding of S p a t i a l Contrast S e n s i t i v i t y 105 Appendix Two Comparison of Threshold Determination f o r S p a t i a l C o n t r ast S e n s i t i v i t y Function 110 Appendix Three D e s c r i p t i o n of Machine Used to Test S p a t i a l C o n t r ast S e n s i t i v i t y i n t h i s Experiment 112 Appendix Four L e t t e r of Consent 114 V L i s t of Tables Page Table 1 E f f e c t of V a r i o u s Ocular A b n o r m a l i t i e s on the Contrast S e n s i t i v i t y F u n c t i o n . 20 Table 2 Parameters that may e f f e c t the Contrast S e n s i t i v i t y F u n c t i o n 24 Table 3 Stimulus and Observer Parameters i n "Age" S t u d i e s 58 Table 4 T - t e s t s between Younger and Older Observers on V a r i o u s Measures 73 Table 5 Group Means (and Standard D e v i a t i o n s ) of I n d i v i d u a l C o n t r a s t Threshold Standard D e v i a t i o n s 80 Table 6 C o r r e l a t i o n C o e f f i c i e n t s between Age and A r i t h m e t i c C o n t r a s t S e n s i t i v i t y 81 Table 7 C o r r e l a t i o n C o e f f i c i e n t s f o r S p h e r i c a l , C y l i n d e r C o r r e c t i o n , Best C o r r e c t e d S n e l l e n A c u i t y , and I n t r a o c u l a r Pressure versus A r i t h m e t i c C o n t r a s t S e n s i t i v i t y (Ascending and O v e r a l l ) 83 Table 8 I n t e r c o r r e l a t i o n s f o r Co n t r a s t S e n s i t i v i t y at a l l S p a t i a l F r e q u e n c i e s (Ascending T r i a l s ) 85 Table 9 I n t e r c o r r e l a t i o n s f o r . C o n t r a s t S e n s i t i v i t y at a l l S p a t i a l F r e q u e n c i e s ( O v e r a l l ) 86 Table 10 I n t e r c o r r e l a t i o n s f o r C o n t r a s t S e n s i t i v i t y at a l l S p a t i a l F r e q u e n c i e s (Descending T r i a l s ) 87 Table 11 Some P r o p e r t i e s of R e t i n a l Ganglion C e l l s i n the Cat and Monkey 109 v i L i s t of F i g u r e s Page F i g u r e 1 A) R e c t i l i n e a r Propagation of L i g h t and Image Formation by a Pinhole B) D i f f r a c t i o n of L i g h t About a Small Aperature 4 F i g u r e 2 Square and Sine Wave G r a t i n g 6 F i g u r e 3 The Summation of Sine Waves to R e a l i z e a Square Wave 7 F i g u r e 4 A T y p i c a l Contrast S e n s i t i v i t y F u n c t i o n 12 F i g u r e 5 A Visuogram 14 F i g u r e 6 A P o s s i b l e E f f e c t of R e t i n a l L a t e r a l I n h i b i t i o n 16 F i g u r e 7 I s o c o n t r a s t S e n s i t i v i t y Curves 16 F i g u r e 8 CSF f o r Square and Sine Wave G r a t i n g s at Two Mean P a t t e r n Luminances 34 F i g u r e 9 Contrast S e n s i t i v i t y f o r S t a b i l i z e d and U n s t a b i l i z e d Sine G r a t i n g s (yellow g r a t i n g s ) 36 F i g u r e 10 E f f e c t of P a t t e r n O r i e n t a t i o n on the CSF 38 F i g u r e 11 H o r i z o n t a l Luminance P r o f i l e s of S t i m u l i used by Van der Wildt and Waarts (1983) 41 F i g u r e 12 Modulation S e n s i t i v i t y as a Fun c t i o n of the Number of C y c l e s f o r Four Mean P a t t e r n Luminances 44 F i g u r e 13 A and B Contrast S e n s i t i v i t y F u n c t i o n s from V a r i o u s "Age" St u d i e s ....55,56 F i g u r e 14 A r i t h m e t i c Mean Contrast S e n s i t i v i t y Functions (Ascending T r i a l s ) f o r Males and Females 70 v i i F i g u r e 15 A r i t h m e t i c Mean Contrast S e n s i t i v i t y F u n ctions (Descending T r i a l s ) f o r Males and Females 71 F i g u r e 16 A r i t h m e t i c Mean Contrast S e n s i t i v i t y F u n ctions (Combined) f o r Males and Females 72 F i g u r e 17 A r i t h m e t i c Mean Contrast S e n s i t i v i t y F u n ctions (Ascending T r i a l s ) f o r Younger and Older Observers 74 F i g u r e 1 8 Geometric Mean Contrast S e n s i t i v i t y F u n ctions (Ascending T r i a l s ) f o r Younger and Older Observers 75 F i g u r e 19 A r i t h m e t i c Mean Contrast S e n s i t i v i t y F u n c t i o n s (Descending T r i a l s ) f o r Younger and Older Observers .... 76 F i g u r e 20 Geometric Mean Co n t r a s t S e n s i t i v i t y F u n ctions (Descending T r i a l s ) f o r Younger and Older Observers .... 77 F i g u r e 21 A r i t h m e t i c Mean Contrast S e n s i t i v i t y F u n ctions (Combined) f o r Younger and Older Observers 78 F i g u r e 22 Geometric Mean Co n t r a s t S e n s i t i v i t y F u n ctions (Combined) f o r Younger and Older Observers 79 F i g u r e 23 A Model ON-center C e l l Responding to Changes i n I l l u m i n a t i o n W ithin i t s Receptive F i e l d Center 106 F i g u r e 24 Cat Ganglion C e l l Responses to a Sine G r a t i n g . 108 F i g u r e 25 Contrast S e n s i t i v i t y Function For Two Methods of T h r e s h o l d Determination 111 v i i i Ac knowledqements I would l i k e to thank the members of my t h e s i s comittee f o r t h e i r h e l p f u l comments and c r i t i c i s m s that served to enhance the q u a l i t y of the experiments undertaken i n t h i s study as w e l l as the f i n a l manuscript that f o l l o w s . Kees Wijsman f o r r e f r a c t i o n of many of the younger s u b j e c t s i n t h i s study and Dr. Drance, Dr. R o l l i n s , and Dr. Mik e l b e r g f o r a l l o w i n g me to request v o l u n t e e r s from t h e i r h o s p i t a l c l i n i c s . And l a s t l y , but by no means l e a s t l y , to Dr. Johnson and John Kozak f o r t h e i r advice on s t a t i s t i c a l treatment of the data. 1 I n t r o d u c t i o n V i s u a l a c u i t y i s of t e n d e f i n e d as the c a p a c i t y to d i s c r i m i n a t e the f i n e d e t a i l s of o b j e c t s i n the f i e l d of view. (Riggs, 1965 p. 321) One u s u a l l y t h i n k s in terms of what i s the sm a l l e s t o b j e c t or element of an ob j e c t that i s v i s i b l e to any given i n d i v i d u a l . C e r t a i n l y , i n a c l i n i c a l s i t u a t i o n at l e a s t , a c u i t y t y p i c a l l y i s repo r t e d as the sm a l l e s t l e t t e r s i z e that i s c o r r e c t l y i d e n t i f i e d by the p a t i e n t . F u r t h e r , i t i s taken f o r granted that an i n d i v i d u a l who i s able to see a small l e t t e r w i l l be able to d e t e c t and c o r r e c t l y i d e n t i f y any l e t t e r s t h a t are l a r g e r . Thus, one value i s f e l t to d e s c r i b e an i n d i v i d u a l ' s v i s u a l a c u i t y . In f a c t , v i s u a l a c u i t y i s much more than the d e t e c t i o n of l e t t e r s that vary i n shape and p h y s i c a l s i z e . For example, v i s u a l a c u i t y has been somewhat a r b i t r a r i l y d i v i d e d i n t o four c a t e g o r i e s (eg. by Riggs, 1965) that vary mostly i n terms of f e a t u r e s of the stimulus and what task i s r e q u i r e d of the subj e c t in a given s i t u a t i o n . These c a t e g o r i e s are d e t e c t i o n , r e c o g n i t i o n ( o f t e n c a l l e d S n e l l e n a c u i t y ) , l o c a l i z a t i o n , and r e s o l u t i o n a c u i t y . In a d e t e c t i o n a c u i t y task, the subject i s u s u a l l y asked to re p o r t on the presence or absence of an o b j e c t i n the f i e l d of view. T h i s o b j e c t may be a spot of l i g h t on a darkened background or a dark o b j e c t on a l i g h t e r background. Included i n t h i s c l a s s a l s o are o b j e c t s whose luminance i s not g r e a t l y d i f f e r e n t than the r e s t of the f i e l d . So the s i z e and i n t e n s i t y of the s t i m u l i are what i s t y p i c a l l y v a r i e d i n t h i s type of a c u i t y task. I f these s t i m u l i c o n s i s t of o b j e c t s with 2 i d e n t i f i a b l e c h a r a c t e r i s t i c s , such as l e t t e r s which vary in shape and p h y s i c a l s i z e and the s u b j e c t i s r e q u i r e d to c o r r e c t l y i d e n t i f y the s t i m u l i , t h i s i s t y p i c a l l y r e f e r r e d to as r e c o g n i t i o n a c u i t y . V a r i a t i o n s of t h i s t e s t u s u a l l y i n v o l v e o b j e c t s of d i f f e r e n t shape--for example an 'E' or a 'C v a r y i n g i n s i z e and set at d i f f e r e n t o r i e n t a t i o n s or even s i l h o u e t t e s of s h i p s or c a r s . These optotypes are o f t e n presented to c h i l d r e n or a d u l t s who are unable to read l e t t e r s . C e r t a i n l y r e c o g n i t i o n a c u i t y i s most o f t e n thought of when the word a c u i t y i s ment ioned. L o c a l i z a t i o n a c u i t y i n v o l v e s d i s c r i m i n a t i o n of small displacements of one p a r t of the stimulus from other p a r t s , so a t h i n v e r t i c a l l i n e broken at i t s halfway p o i n t and the bottom h a l f d i s p l a c e d h o r i z o n t a l l y by a v a r i a b l e amount from the top h a l f would c o n s t i t u t e a stimulus i n t h i s type of task. The s m a l l e s t displacement i d e n t i f i e d c o r r e c t l y c o n s i s t e n t l y would c o n s t i t u t e the v e r n i e r a c u i t y (or l o c a l i z a t i o n a c u i t y ) of an i n d i v i d u a l . Riggs a l s o mentions r e s o l u t i o n a c u i t y . In these s i t u a t i o n s the s t i m u l i i s o f t e n two v e r t i c a l bars that can vary i n p h y s i c a l s i z e but the c r u c i a l f e a t u r e i s the c l o s e s t spacing of the bars that can s t i l l allow the i n d i v i d u a l to see two separate b a r s . Other s t i m u l i used i n t h i s type of task have been two dots, a checkerboard a r r a y , or a bar g r a t i n g p a t t e r n . In each case though, the s u b j e c t i s t e s t e d to f i n d the minimum sepa r a b l e : the minimal d i s t a n c e between o b j e c t s f o r the d i s c r i m i n a t i o n of separateness. Often the bar p a t t e r n used as the stimulus was simply a cardboard p a t t e r n composed of dark ink bars on a white 3 background. V i s u a l a c u i t y was d e f i n e d as the r e c i p r o c a l of angular s e p a r a t i o n between the inner edges of the bars when they were j u s t r e s o l v e d . (Lukiesh and Moss, 1937) G r a t i n g p a t t e r n s were o p t i m a l l y produced by using d i f f r a c t i o n methods. That i s , when l i g h t from a source passes through a small aperature , i t does not completely obey the laws of g e o m e t r i c a l o p t i c s . The image a c t u a l l y becomes l e s s sharp, s c a t t e r e d , or b l u r r e d i n s t e a d of appearing as an i n v e r t e d m i n i a t u r e of the o r i g i n a l source. (See F i g u r e 1.) Using t h i s p r i n c i p l e Byram (1944) took a d i s t a n t l i n e source of monochromatic l i g h t and viewed i t through a double-s l i t diaphragm h e l d so that the s l i t s were p a r a l l e l to the l i n e source. The source then appeared as a luminous r e c t a n g u l a r l y shaped area t r a v e r s e d by a number of very sharp b r i g h t and dark l i n e s . The v a r i a b l e of i n t e r e s t i n t h i s p a r t i c u l a r i nstance was the s m a l l e s t bar s i z e and, once t h i s t h r e s h o l d was found, the background luminance at which the bar p a t t e r n would disappear. V a r y i n g background luminance amounted to changing only the o v e r a l l i n t e n s i t y without a l t e r i n g the d i f f e r e n c e between l i g h t and dark bars. A l t e r i n g o v e r a l l p a t t e r n i n t e n s i t y would seem but a step away from v a r y i n g the luminance of both bars about a c e n t r a l mean value and i t would be tempting to conclude that c o n t r a s t s e n s i t i v i t y was a l o g i c a l p r o g r e s s i o n from t h i s . The next step then being to use bars of d i f f e r e n t widths and f i n a l l y a g r a t i n g p a t t e r n that had a s p a t i a l luminance p r o f i l e that was other than square wave. I n t e r e s t i n g l y , as an a c u i t y t e s t , c o n t r a s t s e n s i t i v i t y to 4 5 g r a t i n g s that have a s p a t i a l luminance p r o f i l e that i s s i n u s o i d a l (see F i g u r e 2) appears to have been adapted from that branch of o p t i c s that concerns i t s e l f with the t r a n s m i s s i o n p r o p e r t i e s of l e n s e s . The q u a l i t y of an o p t i c a l system was based upon i t s a b i l i t y to a c c u r a t e l y t r a n s m i t the image of the o r i g i n a l o b j e c t , that i s without d i s t o r t i o n . S i n u s o i d a l p a t t e r n s were chosen c h i e f l y f o r the f o l l o w i n g reasons. F o u r i e r ' s theorm s t a t e s that any p e r i o d i c waveform or d i s t r i b u t i o n can be generated by summing the c o r r e c t s e r i e s of s i n e waves. T h i s a l s o means that any p e r i o d i c waveform can be broken down i n t o i t s b a s i c elements, namely, a s e r i e s of s i n e waves (see F i g u r e 3). So t h i s p a r t i c u l a r waveform was f e l t to represent a fundamental element, one of the b u i l d i n g blocks of v i s u a l s t i m u l i , as w e l l as being easy to work with mathematically. E a s i e r than say a s e r i e s of independent l i t t l e dots of v a r y i n g luminance. A l s o , as long as the imaging system was l i n e a r the image of the sine wave was i t s e l f a s i n e wave s i n c e s i n e wave g r a t i n g s are "eigen f u n c t i o n s " f o r any l i n e a r imaging system. T h i s meant that one knew in advance what the response of the system should be. No other p e r i o d i c stimulus p a t t e r n has a s i m i l a r p r o p e r t y . U s u a l l y a set of s i n e p a t t e r n s which v a r i e d i n s i z e and c o n t r a s t were imaged through the lens or o p t i c a l system and the r e s u l t i n g image measured and compared to the o r i g i n a l . The d i s c r e p a n c y between the o b j e c t and the o p t i c a l r e p r e s e n t a t i o n of i t was expressed mathematically and u s u a l l y c a l l e d something l i k e the modulation t r a n s f e r f u n c t i o n or o p t i c a l t r a n s f e r f u n c t i o n . A more formal d e f i n i t i o n of t h i s i s as f o l l o w s : A mathematical e x p r e s s i o n of the r e l a t i o n s h i p of the l i g h t d i s t r i b u t i o n i n an o p t i c a l image to that i n the 6 F i g u r e 2: S q u a r e and S i n e Wave G r a t i n g From: Cornsweet, 1970, p.313 A + 8 + C l l l l Position (arbitrary units) F i g u r e 3: The Summation of S i n e Waves to Real a Square Wave From: Cornsweet, 1970, p.315 8 o b j e c t , hence an e x p r e s s i o n of the o p t i c a l r e p r o d u c t i o n or o p t i c a l t r a n s f e r p r o p e r t i e s of the system, o f t e n i n terms of the r a t i o of image c o n t r a s t to o b j e c t c o n t r a s t as a f u n c t i o n of s p a t i a l frequency (of a g r a t i n g t a r g e t ) , hence v a r i o u s l y r e f e r r e d to as c o n t r a s t t r a n s f e r f u n c t i o n , modulation t r a n s f e r f u n c t i o n , frequency response f u n c t i o n , s p a t i a l frequency t r a n s f e r f u n c t i o n , sinewave response f u n c t i o n . I t i s the F o u r i e r transform of the spread f u n c t i o n . ( C l i n e e t . a l . , 1980) I t s mathematical e x p r e s s i o n would be as f o l l o w s : The s p a t i a l d i s t r i b u t i o n of l i g h t i n the g r a t i n g c o u l d be expressed by where p i s the number of l i n e s per m i l l i m e t r e (the s p a t i a l frequency) and x i s the o v e r a l l p a t t e r n s i z e ( u s u a l l y in m i l l i m e t r e s ) and s i n c e was by d e f i n i t i o n the c o n t r a s t of a g r a t i n g and t h e r e f o r e C(p) i s the c o n t r a s t . Now the r e s u l t i n g image, i f the o p t i c a l system was o p e r a t i n g at u n i t m a g n i f i c a t i o n and there was no l o s s of l i g h t , had a 9 d i s t r i b u t i o n given by: L= l +mCp)c(p)£in2Tp^ where M(p) i s a dimensionless constant c a l l e d the modulation t r a n s f e r f a c t o r . The v a r i a t i o n of M(p) with p was c a l l e d the modulation t r a n s f e r f u n c t i o n . (Ditchburn, 1973) U s u a l l y Schade i s c r e d i t e d with being the f i r s t to r e p o r t the response of the human eye to s i n u s o i d a l g r a t i n g p a t t e r n s . However Selwyn's 1948 report precedes Schade's by approximately eig h t y e a r s . Selwyn who worked f o r Kodak i n England was i n t e r e s t e d p r i m a r i l y i n a e r i a l reconnaissance photography and a s s o c i a t e d problems of r e s o l u t i o n of photographs versus r e s o l u t i o n c a p a b i l i t i e s of human observers. H i s examination of the a b i l i t y of human observers to d e t e c t small c o n t r a s t d i f f e r e n c e s to a yellow l i g h t , s i n e p a t t e r n s t i m u l i r e v e a l e d that there was an optimum range f o r c o n t r a s t d e t e c t i o n and that f o r f i n e p a t t e r n s more p h y s i c a l c o n t r a s t was necessary than for t h i s more median optimum range. A l s o , that f o r p a t t e r n s that were c o a r s e r than t h i s optimum range, more p h y s i c a l c o n t r a s t was necessary f o r d e t e c t i o n although the f a l l o f f from the optimum was more gra d u a l . The high frequency i n c r e a s e i n c o n t r a s t necessary f o r d e t e c t i o n he a t t r i b u t e d to the s p a t i a l g r a i n of the receptor moasic and the "...slow r i s e beyond 12 minutes of arc (was) p o s s i b l y a t t r i b u t a b l e to the d i s t u r b i n g e f f e c t s of s c r a t c h e s and 1 0 specks of dust which become obvious at the small p u p i l a peratures which l e a d to such l a r g e angular s e p a r a t i o n s . " (p.10) E v i d e n t l y the poorer performance at the l a r g e r p a t t e r n s i z e s was q u i t e b a f f l i n g to him. Schade (1956) d i d , however, study the response of the eye to sinewave g r a t i n g s f a r more i n t e n s e l y and h i s work seems to have been the major impetus f o r f u r t h e r study u s i n g t h i s s t i m u l u s . He appears, i n t h i s paper at l e a s t , to have been concerned with developing a " p h o t o e l e c t r i c analog of the v i s u a l system" somewhat along the l i n e s of a c o l o u r t e l e v i s i o n camera coupled to a computer. Examination of the v i s u a l performance of the human eye to v a r i o u s s t i m u l i such as incremental b r i g h t n e s s steps, v i s i b i l i t y of poi n t sources and c o n t r a s t t h r e s h o l d s f o r small areas was necessary to make h i s model perform s i m i l a r i l y to the human system. Examining the response of the human system to sinewave g r a t i n g p a t t e r n s (the F o u r i e r s p e c t r a ) was necessary so that the i n t e g r a t i v e p r o p e r t i e s of t h i s imaging system c o u l d be s p e c i f i e d and h i s model would behave a c c o r d i n g l y . Schade's r e s u l t s f o r the human eye were expressed i n terms of normalized sinewave response f a c t o r f o r d i f f e r e n t TV l i n e numbers, where a TV l i n e number was the number of h a l f c y c l e s i n a u n i t l e n g t h . Larger TV l i n e numbers meant f i n e r g r a t i n g p a t t e r n s . I t was not u n t i l other i n d i v i d u a l s began to examine the modulation t r a n s f e r f u n c t i o n of the d i o p t r i c mechanism of the eye and the response of the nervous system to these s t i m u l i that the r e s u l t a n t data came to be expressed i n the form encountered i n the more recent l i t e r a t u r e . ( A r n u l f and Dupuy, 1960; Campbell and Green, 1965; Campbell and Gubisch, 1966; 11 Campbell and Robson, 1968) Now the s p a t i a l frequency was expressed i n c y c l e s per degree of v i s u a l angle i n s t e a d of l i n e s per m i l l i m e t r e (or TV l i n e number) and X i n the p r e v i o u s equation was expressed in terms of degrees i n the v i s u a l f i e l d . A g r a t i n g p a t t e r n , u s u a l l y subtending between 2 and 10 degrees of v i s u a l angle, would be generated on a cathode ray tube. From a homogenous f i e l d , the modulation depth or amplitude of the sinewave would be i n c r e a s e d u n t i l the g r a t i n g became v i s i b l e to the observer. For each s i z e of grating- p a t t e r n the procedure would be repeated. I t was then p o s s i b l e to determine the o v e r a l l s e n s i t i v i t y of the observer to the p a t t e r n s . The t h r e s h o l d responses were u s u a l l y t r a n s f o r m e d - - t h e i r r e c i p r o c a l was taken--so that r e s u l t s c o u l d be expressed i n terms of s e n s i t i v i t y . A l a r g e r value meant that l e s s p h y s i c a l c o n t r a s t was r e q u i r e d from the peak to the trough of the sinewave, that i s the observer was more s e n s i t i v e to c o n t r a s t d i f f e r e n c e s . The o v e r a l l response of the observer to the d i f f e r e n t g r a t i n g s i z e s became known as the "Contrast S e n s i t i v i t y F u n c t i o n " ( a b b r e v i a t e d CSF). A t y p i c a l response curve i s shown in F i g u r e 4. One can see i n t h i s diagram that the more medium s p a t i a l f r e q u e n c i e s are d e t e c t e d with l e s s p h y s i c a l c o n t r a s t than the higher and lower s p a t i a l f r e q u e n c i e s . T y p i c a l l y t h i s curve peaks between 3-6 c y c l e s per degree (cyc/deg). V a r i o u s parameters e f f e c t the shape of the CSF as w e l l as changing the peak s e n s i t i v i t y so, f o r example, were one to use a p a t t e r n with a mean luminance of .05 cd/m 2 i n s t e a d of 500 cd/m 2, the o v e r a l l curve would be g r e a t l y depressed, a t t e n u a t e d above 10 cyc/deg i n s t e a d of at 35 cyc/deg, and d i s p l a y i n g a peak s e n s i t i v i t y at approximately 1 cyc/deg. 12 SPAT IAL FREQUENCY (cycles/degree) F i g u r e 4: A T y p i c a l C o n t r a s t S e n s i t i v i t y F u n c t i o n From: Bodis-Wo11ner, 1976, p.699 1 3 The e f f e c t of mean p a t t e r n luminance i s shown in F i g u r e 8. T h i s e f f e c t i s f u r t h e r d i s c u s s e d along with the e f f e c t of other stimulus parameters and observer c h a r a c t e r i s t i c s on the CSF on pages 19 to 64. Aside from a l t e r i n g the CSF by manipulations of the stimulus or by changing i t s appearance by numerical manipulation such as using l o g values, another method for d i s p l a y i n g c o n t r a s t s e n s i t i v i t y o f t e n c a l l e d a visuogram ( a f t e r audiogram) has been used (eg. Bodis-Wollner and Diamond, 1976). A sample visuogram i s shown i n F i g u r e 5. U s u a l l y such a method of p r e s e n t a t i o n i s used to accentuate the l o s s i n c u r r e d due to pathology. In f a c t t h i s p r e s e n t a t i o n method i s not widespread and h a r d l y ever appears in other than s t u d i e s of o c u l a r abnormality and the CSF. Selwyn a s i d e , the f a l l o f f in the CSF curve at high s p a t i a l f r e q u e n c i e s i s p r i m a r i l y due to q u a l i t i e s of the d i o p t r i c mechanism of the eye. A l l l i n e a r l e n s systems e x h i b i t high frequency c u t o f f . T h i s i s due mainly to lens a b e r r a t i o n and d i f f r a c t i o n e f f e c t s . P o s s i b l y , f o r the eye, other f a c t o r s such as r e t i n a l d i f f u s i o n , tremor, and d r i f t eye movements serve to degrade the image as w e l l . The decreased s e n s i t i v i t y to low s p a t i a l f r e q u e n c i e s i s more d i f f i c u l t to e x p l a i n s i n c e l i n e a r imaging systems do not have low frequency a t t e n u a t i o n . Most e x p l a n a t i o n s of poor c o n t r a s t s e n s i t i v i t y to low s p a t i a l frequency g r a t i n g s are based upon the e f f e c t s of l a t e r a l i n h i b i t i o n , the r e c e p t i v e f i e l d p r o p e r t i e s of r e t i n a l ganglion c e l l s and the f u n c t i o n a l d i f f e r e n c e s between the 'X'-type and the 'Y'-type g a n g l i o n c e l l s . Cornsweet (1970, p.358-359) proposed that decreased i 1 — i 1 1 r ~ 1 2 5 10 20 40 SPAT IAL F R E Q U E N C Y F i g u r e 5: A Visuogram Bodis-Wol1ner , 1976, p . 700 1 5 s e n s i t i v i t y to g r a t i n g s of low s p a t i a l frequency was due to l a t e r a l i n h i b i t o r y connections of adjacent p h o t o r e c e p t o r s . These connections a ct to accentuate abrupt changes in the s p a t i a l i n t e n s i t y d i s t r i b u t i o n of a stimulus s i n c e " . . . r e c e p t o r s j u s t on the b r i g h t s i d e of the input edge are r e c e i v i n g r e l a t i v e l y l e s s i n h i b i t i o n because they are near a dimly l i t a r e a , " and the re c e p t o r s on the dark si d e are r e c e i v i n g maximal i n h i b i t i o n from the adjacent a c t i v e l y f i r i n g r e c e p t o r s that are responding to the b r i g h t stimulus so the r a t e of f i r i n g of the "dark" r e c e p t o r s i s g r e a t l y supressed. T h i s means that a stimulus with a small rate of change i n s p a t i a l l u m i n a n c e — s u c h as a low c o n t r a s t low s p a t i a l frequency grating--would evoke none or l i t t l e of t h i s edge enhancement. T h i s e f f e c t i s diagrammed i n Fi g u r e 6 f o r v a r i o u s g r a d i e n t s of l i g h t d i s t r i b u t i o n . Such l a t e r a l i n h i b i t i o n has been c o n v i n c i n g l y demonstrated i n the Limulus (horseshoe crab) by H a r t l i n e and R a t l i f f (1957). Perhaps amacrine or h o r i z o n t a l c e l l s i n the human r e t i n a perform some i n h i b i t o r y f u n c t i o n of t h i s kind but c o n c l u s i v e evidence of t h i s i s l a c k i n g (at l e a s t to t h i s w r i t e r ) . The d i f f e r e n t p r o p e r t i e s of the r e t i n a l g a n g l i o n c e l l s examined i n animals other than homo sapiens has l e d to v a r i o u s hypotheses about what r e t i n a l elements are r e s p o n s i b l e for or p r e f e r e n t i a l to si n e p a t t e r n s of v a r i o u s s p a t i a l frequency i n the human. A more complete d i s c u s s i o n of the p r o p e r t i e s of these gangl i o n c e l l s as determined by u n i c e l l u l a r m i c r o e l e c t r i c r e c o r d i n g techniques i n animals can be found in Appendix One. Based upon r e t i n a l d i s t r i b u t i o n (predominately f o v e a l ) , r e c e p t i v e f i e l d s i z e ( s m a l l ) , and conduction v e l o c i t y (slow) i t F i g u r e 6: A P o s s i b l e E f f e c t of R e t i n a l L a t e r a l I n h i b i t ion From: Cornsweet, 1970, p.359 17 i s f e l t that higher s p a t i a l f r e q u e n c i e s are p r e f e r e n t i a l l y processed by the X type ga n g l i o n c e l l s . Y type are f e l t to be more s e l e c t i v e f o r lower s p a t i a l f r e q u e n c i e s s i n c e they have l a r g e r c e n t e r s , and are l e s s abundant i n the fovea. They a l s o appear to be more s e n s i t i v e to movement as they e x h i b i t p e r i p h e r y e f f e c t (response to a small spot of l i g h t i n remote part of r e c e p t i v e f i e l d ) and have s h o r t e r l a t e n c i e s and f a s t e r conduction v e l o c i t i e s than do X or W type. While the presence of X and Y type c e l l s i n the human has not been documented p h y s i o l o g i c a l l y ( f o r obvious rea s o n s ) , p s y c h o p h y s i c a l measurements do support the presence of some f u n c t i o n a l g a n g l i o n c e l l dichotomy i n the human r e t i n a . For example i t has been shown that temporal modulation of a s i n e g r a t i n g p a t t e r n p r e f e r e n t i a l l y enhances low s p a t i a l f r e q u e n c i e s over higher ones, (see F i g u r e 13-B: Sekuler and Hutman, 1980 diagram) A l s o when s u b j e c t s viewed g r a t i n g p a t t e r n s with a c e n t r a l l y s t a b i l i z e d 3.2 degree scotoma i n a 5.4 degree t a r g e t that was temporally modulated e i t h e r a b r u p t l y (square wave) or g r a d u a l l y (sine wave), the l o s s of c e n t r a l v i s i o n maximally e f f e c t e d the highest s p a t i a l f r e q u e n c i e s and abrupt temporal modulation enhanced o n l y low s p a t i a l frequency c o n t r a s t s e n s i t i v i t y . (Higgins e t . a l . , 1983) One assumes that somehow these i n d i v i d u a l g a n g l i o n c e l l s group t h e i r responses to f u r n i s h the o v e r a l l c o n t r a s t s e n s i t i v i t y f u n c t i o n . Even though how t h i s grouping i s accomplished i s not c l e a r , and the f u n c t i o n a l dichotomy demonstrated by En r o t h - C u g e l l and Robson has been shown to be not so c l e a r cut ( r e c a l l the W types mentioned i n Appendix One) 18 or at l e a s t d i f f e r e n t i a b l e by other c r i t e r i a than l i n e a r i t y of c e n t e r - s u r r o u n d , t h i s c l a s s i f i c a t i o n system has proven very u s e f u l i n many s i t u a t i o n s as a way to understand processes at work i n the v i s u a l system. For example, the X-Y dichotomy has l e d to a r e e v a l u a t i o n of c e r t a i n d i s e a s e p r o c e s s e s . Researchers who were examining the type of v i s u a l l o s s e s found i n o c u l a r p a t h o l o g i e s r e a l i z e d that c e r t a i n types of g a n g l i o n c e l l s may be a f f e c t e d more than or at l e a s t p r i o r to other types. The p o s s i b i l i t y e x i s t e d that some v i s u a l s t i m u l i may d e t e c t these f u n c t i o n a l a b n o r m a l i t i e s before a c t u a l p h y s i c a l damage oc c u r r e d . C o n s i d e r i n g t h a t the fundamental b a s i s f o r the c l a s s i f i c a t i o n system (X, Y type) was response to a s i n e g r a t i n g , and that X and Y type c e l l s seemed p r e f e r e n t i a l to d i f f e r e n t s p a t i a l f r e q u e n c i e s , i t appeared q u i t e l o g i c a l to examine the CSF i n o c u l a r pathology. In a d d i t i o n , an understanding of the o c u l a r e f f e c t of a d i s e a s e on the CSF c o u l d l e a d to more knowledge about normal f u n c t i o n i n g i f the p a t h o l o g i c change of a given d i s e a s e was w e l l known. Since pathology i s an important v a r i a b l e to c o n s i d e r i n s t u d i e s of the aging, i t w i l l be mentioned here. 19 V a r i a b l e s E f f e c t i n g the Contrast S e n s i t i v i t y Function  A) C h a r a c t e r i s t i c s of the Observer 1) Ocular Pathology The f o l l o w i n g i s a b r i e f summary of the e f f e c t of v a r i o u s o c u l a r p a t h o l o g i e s on the c o n t r a s t s e n s i t i v i t y f u n c t i o n . While the r e f e r e n c e s used are by no means exhaustive, they do represent a f a i r sample of the repor t e d research on each of these d i s e a s e s t a t e s . The e f f e c t of amblyopia, macular degeneration, r e t i n a l detachment, d i a b e t i c r e t i n o p a t h y , o p t i c n e u r i t i s and c h r o n i c simple glaucoma on the c o n t r a s t s e n s i t i v i t y f u n c t i o n are given i n Table 1. A l s o i n c l u d e d i n t h i s t a b l e are the v a r i o u s s t i m u l u s parameters u t i l i z e d in each rep o r t e d study. It can be seen from t h i s t a b l e that few re s e a r c h e r s use i d e n t i c a l methods of t e s t i n g or t h r e s h o l d c r i t e r i a . In general computer c o n t r o l l e d o s c i l l o s c o p e s or video type d i s p l a y s allow the t e s t e r to e a s i l y u t i l i z e s t a i r c a s e methods and random p r e s e n t a t i o n of s p a t i a l f r e q u e n c i e s f o r t h r e s h o l d d e t e r m i n a t i o n while i n d i v i d u a l s u sing apparatus such as l a s e r i n t e r f e r o m e t r y that are under manual c o n t r o l use only ascending t r a i l s to determine t h r e s h o l d . Those using the Arden p l a t e s vary c o n t r a s t from low to high as each p l a t e i s uncovered by the t e s t e r so t h i s c o u l d be co n s i d e r e d an ascending t r i a l with only one t h r e s h o l d d e t e r m i n a t i o n . One should a l s o note the range of mean t a r g e t luminances used (10-300 cd/m 2) and the v a r i e t y of t a r g e t surrounds employed. Both mean t a r g e t luminance and adapting surround e f f e c t the c o n t r a s t 2 0 T a b l e 1: E f f e c t of V a r i o u s O c u l a r A b n o r m a l i t i e s on t he C o n t r a s t S e n s i t i v i t y F u n c t i o n METHOOOLOGY R e s u l t s D i s e a s e How g e n e r a t e d S t I m u l u s Size Mean B a c k g r o u n d Spa t i a 1 f r e q u e n c i e s t e s t e d T h r e s n o 1 d Tempora1 Number o f S u b j e c t s C o m p a r i s o n Group E f f e c t on the CSF ( R e f e r e n c e ) Pa t t e r n I n t e n s t t y Cr i t e r i a Modu1 a t i or l turn i nance Amb I v'OP 1 3 ( H e s s a n d H o w e l l . 1977) 3 . 7' , t . 3' NO (0 HZ) 4 fe11ow une f f e e t e d Some Mod If"Ied 30 c d / m ' same a 1 so not s t a t e d ( d i a g r a m s o n l y ) s ta i r c a s e eye ( w h i c h a p p e a r e d - h i g h f r e q u e n c y a b n o r m a l i t y Osc t 1 1 o s c o p e (up to 10 co1 ou r m e thod s i m i l a r to a g r o u p O t h e r s (P3 1 e y e / d e g ma t c h e d (5 r e a d i ngs) of n o r m a l s ! - o v e r a l l d e p r e s s i o n ( l o s s at a l l s p a t i a l f r e q u e n c i e s t e s t e d ) p h o s p h o r ) 3.7' f i e l d ) ( L u n d h e t . a l . , 198 I) Osc i11oscope 4.5" by 5.0" 120 c d / m ' 20 cd/m' .5-40 c y c / d e g 3 a s c e n d i n g NO 1 age ma t c h e d norma 1s h f gh f r e q u e n c y l o s s ( v i s u a l a c u i t y 0 . 6 ) L o s s d i s a p p e a r e d (P3 1 ) (19 s p a t i a l f r e q u e n c i e s ) t r i a l s p e r when v i s u a l a c u i t y improved t o 1.0) f r e q u e n c y M a c u l a r O e a e n e r a t 1 on ( S k a i k a . 1980a) A r d e n p l a t e s ? 7 f t . c a n d l e s 0.2. .4. .8. i . S . f i r s t d e t e c t NO n o t s t a t e d age matched e l e v a t e d A r d e n s c o r e ( a c h i e v e d by summing p e r f o r m a n c e 3.2 and 6.4 c y c / d e g p a t t e r n as on a l l p l a t e s ) v a r i a b l e c o n t r a s t p l a t e i s u n c o v e r e d K u h n t - d u n i u s ( K J ) J u v e n i 1 e M a c u l a r O y s t r o p h y (JM) ( H y v a r i n e n e t . a l . . 1983) C a t h o d e r a y 24 by 20 cm. 10 Cd/m' s u r r o u n d not s t a t e d but 1 ) d e t e c t s t i m u l u s 2 norma 1 pepu1 a t ton KJ-20* -norma 1 low s p a t i a l f r e q u e n c y . p o o r e r med ium and ht gh sp a t i a 1 f r e q . d i s p l a y v a r i ed masked by a p p e a r s < 10 c y c / d e g movement or on .5 s e c . 2 5" - l o s s a t a l l frequencies (P4) v i ew1ng b l ack 2) p a t t e r n JM-20* normal low s p a t i a l f r e q u e n c y , h i g h and medium l o s s d1 s t a n c e c a r d b o a r d or i e n t a t i on -5" l o s s a t a l 1 f r e q u e n c i e s (20* and 5' ) ( L o s h i n and W h i t e . 1984) O s c 1 1 1 o s c o p e 5' 100 cd/m' room 1 i ght i ng .5-30 e y e . d e g a t l e a s t s t a i r c a s e NO 8 1 s u b j e c t l o s s a t a l l s p a t i a l f r e q u e n c i e s (P31) 40 cd/m' 5 f o r e a c h p e r s o n b u t method ( a t (u s e o f 2 - 3 x magn i f i c a t i on t e l e s c o p e i n c r e a s e d c o n t r a s t j v a r i e d between s u b j e c t s l e a s t one s e n s i t i v i t y f o r a l l s p a t i a l f r e q u e n c i es but s t i l l we 11 below norma 1 ) a s c e n d i ng. d e s c e n d i n g ) Rs3TT3Ched r e t i n a f i n v o l v i n q the macu1 a) t A n a e r s c n and S j o s t r a n d . 1981) c a t h o d e r a y 1.4" by 1.4* 135 cd/m' 20 cd/m' 15 f r e q u e n c i e s t e s t e d m i n . 2 NO 7 age matched pos t o p e r a t i ve d i sp1 ay 1.4-38 c y c / d e g ( e v e r y 1 db)' a s c e n d i n g (5 e y e s ) l o s s m a i n l y a t i n t e r m e d i a t e and h i g h s p a t i a l f r e q u e n c i e s some r e c o v e r y shown a f t e r l o n g d u r a t i o n p o s t o p e r a t i v e l y D i a b e t i c P e t i nooa t h y ( D r e s s i e r and Rassow. 1981) He-Ne l a s e r 5" 150 cd/m' dark 1-46 e y e . d e g 5 a s c e n d i n g NO 2: 58 y r s . n o r m a l s 95 ey e s to l o g a r i t h m i c a l l y 71 y r s . (12-7 1 y r s . ) l o s s a t a l l s p a t i a l f r e q u e n c i e s equ i d i s t a n t s t e p s ( S o k o i e t . a l . . 1985) v i d e o s y s t e m 4.4" by 5 .6* 100 cd/m' not g i v e n 6 fr o m .5-22.8 c y c / d e g •7 NO 31 insu1i n dep. age matched N o n i n s u l i n d e D . I n s u l i n d e o . i n apx. one o c a v e s t e p s 33 n o n i n s u l i n dep. A) Ret i n o p a t h y o o s e r v a o l e ( n = i 7 ) B) Not o b s e r v a b l e (N=i6) (no r e t i n o p a t n y ) s t a t i s t i c a l l y s i g n i f i c a n t l y s t a t i s t ) c a l l y s i g n i f i c a n t norma 1 a t a l l p o o r e r t h a n norma 1 a t a 11 d i f f e r e n e e o n l y a t s p a t i a l s p a t i a 1 f r e q u e n c i e s 22.B c y c / d e g f r e q u e n c i e s O p t 1 c Neur i t i s/A t r o o n v 1 1 ( D r e s s i e r and Rassow 1981] see under D i a b e t 1c r e t 1nopathy above 1 e y e as a b o v e l a r g e l o s s a t low s p a t i a l f r e q u e n i c e s o t h e r s p a t i a l f r e q u e n c i e s 1oss but not as marked (Tagami e t . a l . . 1980) He-Ne l a s e r 5* 300 t d . I.S. 2. 3, 4, 5. 6. 10. 14, more t h a n NO 27 e y e s r e c o v e r e d 30 s u b j e c t s A t r o p h i c s t a a e of raaculooapi11ar b u n d l e s (apx. 30 20. 30 c y c / d e g 6 a s c e n d • n g o p t i c n e u r o p a t h i e s ( 1 6-50 y r s . ) 1J ( m i l d ) o n l y 3 c y c / d e g p o o r e r c d / m ' ) v . a . < 1 .0 2) 1.5. 2, 3. 4. 7. 30 c y c / d e g p o o r e r 3) ( s e v e r e ) s t a t i s t i c a l l y s i g n i f i c a n t l y p o o r e r a t a l l s p a t i a l f r e q , ( H y v a r i n e n e t . a l . . 1983) see under m a c u l a r d e g e n e r a t i o n above 5 e y e s h e r 1 d i t a r y as a b o v e 4 0* f i e l d s i z e - o v e r a 1 1 l o s s but ma i n l y a t h i g h s p a t i a l f r e q u e n c i e s a l s o 10' j o p t i c a t r o p h y 20* f i e l d s i z e - m o r e marked o v e r a l l l o s s a l s o 40" J 10* f i e l d s i r e - e x t r e m e l o s s a t a l l s p a t i a l f r e q u e n c i e s G1aucoma I (Tagami e t . a l . . 1980) see under opt i c n e u r i t i s / a t r o p h y above 12 p a t i e n t s 30 s u b j e c t s " e a r ] y " g l a u c o m a : p a r a c e n t r a 1 scotoma (v.a.<1.0) ( 1 6-50 y r s . ) *ii t h o r w i t h o u t s 1 i g h t n a s a l st ep s t a t i s t i c a l l y s i g n i f i c a n t d e c r e a s e a t 3 and 4 c y c / d e g ( P h e l p s and M o t o l k o . 1983 ) He-Ne l a s e r i o t g i v e n "tot g i v e n s e v e r a i 3 t l e a s t NJO 13 e y e s ;e11ow eye 3/13 no d i f f e r e n c e , i n 4/13 p o o r e r a t 3 c y c / d e g but a l l o t h e r s d e p r e s s e d i a s c e n d i n g / 13 b e t t e r t h a n u n e f f e c t e d eye ( R o s s e t . a 1 .. 1984 ) ( )s c i 1 1 o s c o p e JO by 20 cm. 300 cd/m' "iot g i v e n 4. . 9 5 . 2 . 8 8 . r nean of t n r e e it 2 80 em. -73. 12.7. -19.25 • e v e r s a 1 s M O 50 s u b j e c t s sge matched ?4 s u b j e c t s l o s s at a l l s p a t i a l f r e q u e n c i e s »px . 6' s t a i r c a s e 53 s u b j e c t s ) 6 s u b j e c t s l o s s a t h i g h s p a t i a 1 f r e o u e n c i e s o n l y eenn i q u e ) i sub 1 e c t s l o s s a t low s p a t i a l f r e q u e n c i e s o n l y i s u b j ec t s no l o s s e s e v i d e n t 21 s e n s i t i v i t y f u n c t i o n and t h e r e f o r e any comparisons between s t u d i e s are s u b j e c t to the e f f e c t of t h i s v a r i a b l e as w e l l . P o s s i b l y , though, f u l l y photopic mean p a t t e r n luminances would y i e l d s i m i l a r r e s u l t s . C e r t a i n l y background luminance i s an important c o n s i d e r a t i o n as i t w i l l e f f e c t the o v e r a l l s t a t e of adaptati o n of the eye as w e l l as, c o n c e i v a b l y , enhancing or l e s s e n i n g edge e f f e c t s between t a r g e t and surround depending whether the background i s l e s s e r (or greater) than or equal to the mean t a r g e t luminance. I t i s p o s s i b l e a l s o that c h o i c e of surround changes d i s c r i m i n a t i o n as i n a p e r i m e t r i c s i t u a t i o n where ch o i c e of background luminance i n f l u e n c e s what the t h r e s h o l d value of the stimulus w i l l be ( i e changes the A l ) . Perhaps the most i n t e r e s t i n g p o i n t to emerge from the wide v a r i e t y of stimulus parameters employed i s that of o v e r a l l p a t t e r n s i z e . If one f o l l o w s the report from Hyvarinen e t . a l . (1983), l a r g e f i e l d s i z e s favour low s p a t i a l f r e q u e n c i e s . Stated another way, small f i e l d s i z e s uncover low frequency l o s s not evident at l a r g e r t a r g e t subtenses. For t h i s v a r i a b l e to be u t i l i z e d most e f f e c t i v e l y , angular, subtense i s best v a r i e d by changing the p h y s i c a l s i z e of the stimulus r a t h e r than v a r y i n g viewing d i s t a n c e s i n c e d i o p t r i c c o r r e c t i o n must be c a r r i e d out for each t e s t i n g d i s t a n c e u t i l i z e d . A l t e r i n g viewing d i s t a n c e to r e a l i z e a l a r g e range of s p a t i a l f r e q u e n c i e s — a p r a c t i s e o f t e n followed by many i n d i v i d u a l s — c a n l e a d t h e r e f o r e to spurious r e s u l t s s i n c e i n many cases the p h y s i c a l dimensions of the s t i m u l i are not a l t e r e d as d i s t a n c e i s changed, (see p. 37) Perhaps t h i s v a r i a b l e w i l l prove a u s e f u l one to apply to other o c u l a r d i s e a s e s . I f o v e r a l l p a t t e r n s i z e i s an important 22 c o n s i d e r a t i o n f o r low s p a t i a l frequency c o n t r a s t s e n s i t i v i t y , then the Arden p l a t e s with such a l a r g e o v e r a l l angular subtense of at l e a s t 30 degrees perhaps would not uncover low s p a t i a l frequency l o s s i n a l l s i t u a t i o n s . In sum,it appears that high and medium s p a t i a l frequency l o s s i s common to most o c u l a r d i s e a s e s . T h i s i s always the case when v i s u a l a c u i t y ( S n e l l e n ) i s poor and appears a l s o to be so when the d i s e a s e i s q u i t e pronounced. Low s p a t i a l frequency l o s s — i n d e p e n d e n t of a medium and high s p a t i a l frequency component — i s r e p o r t e d i n cases of o p t i c n e u r i t i s and i n glaucomatous i n d i v i d u a l s although i n the l a t t e r case most glaucoma caused l o s s e s are r e p o r t e d to be i n the medium and high s p a t i a l f r e q u e n c i e s . I t should a l s o be noted that these low s p a t i a l frequency l o s s e s o c c u r r e d i n i n d i v i d u a l s with good S n e l l e n a c u i t i e s and many but by no means a l l high and medium frequency l o s s e s c o u l d a l s o be observed even though S n e l l e n a c u i t y was good. It does not appear to be p o s s i b l e at present to make any s o r t of statement about what type of f u n c t i o n a l or anatomical d e f i c i t s a poor CSF i n d i c a t e s based upon the performance of these i n d i v i d u a l s with v a r y i n g p a t h o l o g i e s . P o s s i b l y more knowledge of e x a c t l y what elements are p r i m a r i l y e f f e c t e d and the pathogenesis of each abnormality would e l u c i d a t e the mechanisms i n the v i s u a l system r e s p o n s i b l e f o r components of the CSF. S t i l l , though, based upon our knowledge of the e f f e c t of stimulus parameters on the CSF i t should be p o s s i b l e to p i c k stimulus parameters f o r the d e t e r m i n a t i o n of the CSF to o p t i m a l l y uncover abnormality i n the v i s u a l system. 23 There seems l i t t l e doubt that the presence of o c u l a r pathology w i l l r a i s e c o n t r a s t s e n s i t i v i t y t h r e s h o l d s . C e r t a i n l y t h i s must be c o n s i d e r e d when one wishes to undertake s t u d i e s of c o n t r a s t s e n s i t i v i t y . Most i n d i v i d u a l s would say such a c o n s i d e r a t i o n i s very obvious and h a r d l y s u b t l e . Not a l l v a r i a b l e s that e f f e c t the CSF however are so d i r e c t l y obvious. Nor i s there u n i v e r s a l agreement on the e f f e c t of some of these v a r i a b l e s even though s e v e r a l of them have been e x t e n s i v e l y examined. These v a r i a b l e s are l o o s e l y grouped a c c o r d i n g to whether they are manipulations of the s i n u s o i d a l stimulus i t s e l f or c h a r a c t e r i s t i c s of the observer. Such an o r g a n i z a t i o n of course i s somewhat a r b i t r a r y s i n c e a l l the parameters u l t i m a t e l y r e l a t e to the v i s u a l system of the o bserver. A l i s t of these parameters and t h e i r groupings i s given i n Table 2. 2) Gender U s u a l l y t h i s p o s s i b l e e f f e c t i s mentioned a n e c d o t a l l y i f at a l l . The general consensus i s that there i s no d i f f e r e n c e i n c o n t r a s t s e n s i t i v i t y between groups that d i f f e r s o l e l y on the b a s i s of gender. One paper however r e p o r t s that c o n t r a s t s e n s i t i v i t y i s d i f f e r e n t f o r i n d i v i d u a l s of d i f f e r e n t gender. Brabyn and McGuinness (1979) repo r t e d on 36 i n d i v i d u a l s who performed ascending c o n t r a s t t h r e s h o l d judgements to e i t h e r v e r t i c a l , h o r i z o n t a l , or o b l i q u e l y o r i e n t e d g r a t i n g s at 13 s p a t i a l f r e q u e n c i e s (.4,.6,.8,1,2,3,...,10 cyc/deg.). A n a l y s i s of v a r i a n c e showed no s i g n i f i c a n t main e f f e c t of sex but a s i g n i f i c a n t two-way sex by s p a t i a l frequency i n t e r a c t i o n [F(12,408)= 2.563 p<.01]. Scheffe comparisons found s i g n i f i c a n t d i f e r e n c e s at o n l y s i x s p a t i a l f r e q u e n c i e s . Females had s u p e r i o r T a b l e 2: Parameters t h a t may e f f e c t the C o n t r a s t S e n s i t i v i t y F u n c t i o n C h a r a c t e r i s t i c s of the Ob s e r v e r 1) O c u l a r P a t h o l o g y 2) Gender 3) Response B i a s 4) Monocular v s . B i n o c u l a r v i e w i n g 5) P u p i l S i z e 6) R e f r a c t i v e S t a t e of Eye 7) Age 8) L o c a t i o n on R e t i n a C h a r a c t e r i s t i c s of the St i m u l u s 1) S i n e wave vs. Square wave 2) Temporal M o d u l a t i o n and Shape of Temporal Envelope 3) G r a t i n g O r i e n t a t i o n 4) Presence of Edges i n the Stimulus F i e l d 5) Target S i z e or Number of P e r i o d s i n the Stimulus F i e l d 6) Mean Luminance of P a t t e r n 7) Luminance of Background 8) C o l o u r of P a t t e r n 9) Method of De t e r m i n i n g T h r e s h o l d 25 c o n t r a s t s e n s i t i v i t y at .4,.6, and .8 cyc/deg and males at 8.0, 9.0 and 10 cyc/deg [p<.00l]. I t i s q u i t e p o s s i b l e t h a t the h i g h l y s i g n i f i c a n t main e f f e c t of s p a t i a l frequency [F(12,408)=264.165 p<.00l] i s c o n t r i b u t i n g most of the observed s i g n i f i c a n c e i n the two-way sex by s p a t i a l frequency i n t e r a c t i o n and not the n o n s i g n i f i c a n t main e f f e c t of sex. That t h i s i s so i s f u r t h e r supported by the a c t u a l group mean c o n t r a s t t h r e s h o l d values (not c o n t r a s t s e n s i t i v i t y v a l u e s ) themselves. One cannot help but n o t i c e the small group mean d i f f e r e n c e s and the l a r g e o v e r l a p between the groups. In f a c t the mean scores at each s t a t i s t i c a l l y s i g n i f i c a n t s p a t i a l frequency l i e l e s s than one standard d e v i a t i o n a p a r t . 3) Response Bia s There i s l i t t l e doubt that changing one's v i s i b i l i t y c r i t e r i a w i l l e f f e c t the t h r e s h o l d c o n t r a s t value. While systematic manipulations of mo t i v a t i o n by va r y i n g reward and punishment have been shown to i n f l u e n c e the p r o b a b i l i t y of a response f o r t h r e s h o l d d e t e c t i o n of v a r i o u s types of s t i m u l i , there appear to be no such s t u d i e s u s i n g s i n u s o i d a l s p a t i a l p a t t e r n s as a st i m u l u s . While i t i s t r u e that Hutman and Sekuler (1980) used a s i g n a l d e t e c t i o n paradigm and a sine g r a t i n g p a t t e r n , they made no attempt to manipulate the observer's response b i a s . T h i s i s understandable as they were seeking to f i n d whether there was an e x i s t i n g d i f f e r e n c e between two groups. C e r t a i n l y though, a changing v i s i b i l i t y c r i t e r i o n c o u l d l e a d to in c r e a s e d v a r i a n c e i n that i n d i v i d u a l ' s t h r e s h o l d values and c o n t r i b u t e to a l a r g e r group v a r i a n c e i f d i f f e r e n t i n d i v i d u a l s have d i f f e r e n t response c r i t e r i a even though they 26 might have s i m i l a r v i s u a l a n a t o m i c a l / f u n c t i o n a l c h a r a c t e r i s t i c s . 4) Monocular versus B i n o c u l a r viewing Over a wide range of s p a t i a l f r e q u e n c i e s (.5-30 cyc/deg) b i n o c u l a r c o n t r a s t s e n s i t i v i t y appears to be s u p e r i o r to monocular. The o v e r a l l shape of the curves appear almost i d e n t i c a l and group mean scores g e n e r a l l y l i e w i t h i n one standard d e v i a t i o n of each other. When r a t i o s are computed that are based upon the i n d i v i d u a l ' s monocular versus b i n o c u l a r mean c o n t r a s t s e n s i t i v i t y at each s p a t i a l frequency, these r a t i o s show a tendency to in c r e a s e with s p a t i a l frequency. ( D e r e f e l d t e t . a l . , 1979) 5) P u p i l S i z e P u p i l s i z e i s not a t r i v i a l c o n s i d e r a t i o n when viewing CRT generated g r a t i n g p a t t e r n s . Woodhouse (1975) examined the e f f e c t of -pupil s i z e on. d e t e c t i o n of square wave g r a t i n g s at v a r i o u s mean ta r g e t luminances and f o r v a r i o u s c o n t r a s t l e v e l s . In ge n e r a l , the 2, 3 and 4 mm. diameter a r t i f i c i a l p u p i l s a f f o r d e d the highest r e s o l u t i o n - - t h e maximum r e s o l v a b l e s p a t i a l f r e q u e n c y — f o r a l l c o n t r a s t l e v e l s at the higher mean p a t t e r n luminances (137.04, 43.17, 13.7, and 4.32 cd/m 2 f o r c o n t r a s t s of .97, .67 and .11). At low l e v e l s (.01 cd/m 2), the l a r g e r diameter p u p i l s proved s u p e r i o r . I t should be noted that d i f f e r e n c e s at these lower l e v e l s are s m a l l , u s u a l l y l e s s than 2 cyc/deg gain i n c u t o f f s p a t i a l frequency as one in c r e a s e s p u p i l s i z e . The l a r g e s t e f f e c t was at .14 cd/m 2 of mean p a t t e r n luminance w h e r e — f o r .97 c o n t r a s t — t h e maximum r e s o l v a b l e 27 s p a t i a l frequency i n c r e a s e d from 10 cyc/deg for a 1 mm p u p i l to 20 cyc/deg f o r a 5 mm p u p i l and decreased to 17 cyc/deg with an 8 mm. p u p i l . Campbell and Green (1965) examined the e f f e c t of p u p i l diameter on c o n t r a s t s e n s i t i v i t y to s i n u s o i d a l g r a t i n g s generated on a cathode ray tube. A 2.0 mm. diameter p u p i l proved s u p e r i o r to 3.8 and 5.8 mm. f o r h i g h e r s p a t i a l f r e q u e n c i e s with no d i f f e r e n c e at the lowest frequency t e s t e d . U n f o r t u n a t e l y these r e s u l t s are confounded by change in mean p a t t e r n luminance as they p l a c e d n e u t r a l d e n s i t y f i l t e r s i n f r o n t of the eye at the l a r g e r p u p i l diameters to equate the amount of r e t i n a l i l l u m i n a t i o n f o r a l l p u p i l s i z e s . So they t e s t e d at d i f f e r e n t mean p a t t e r n luminances f o r d i f f e r e n t s p a t i a l f r e q u e n c i e s . 6) R e f r a c t i v e State of Eye A l t e r i n g the lens power away from the optimum s p e c t a c l e c o r r e c t i o n maximally e f f e c t s the h i g h e s t s p a t i a l f r e q u e n c i e s . Campbell and Green (1965) v a r i e d l e n s power and examined t h i s e f f e c t on c o n t r a s t s e n s i t i v i t y t o s i n u s o i d a l g r a t i n g s at 30, 22, 9 and 1.5 cyc/deg on a cathode ray tube. At 1.5 cyc/deg, changing lens power by as much as ± 2.5 d i o p t e r s had minimal e f f e c t on c o n t r a s t s e n s i t i v i t y . For the other s p a t i a l f r e q u e n c i e s however d e v i a t i o n from the optimum r e s u l t e d i n poorer c o n t r a s t s e n s i t i v i t y . In g e n e r a l the higher the s p a t i a l frequency, the more marked was the e f f e c t of even s l i g h t a l t e r a t i o n of l e n s power. For example^ an i n c r e a s e of +.05 d i o p t e r s caused a decrease in c o n t r a s t s e n s i t i v i t y from approximately 20 to 10 u n i t s . P o s i t i v e or negative c o r r e c t i o n changes r e s u l t i n n e a r l y i d e n t i c a l decreases. E v i d e n t l y , c a r e f u l 28 r e f r a c t i v e c o r r e c t i o n i s q u i t e important at l e a s t f o r higher s p a t i a l f r e q u e n c i e s . 7) Age See pages 53 to 64. 8) L o c a t i o n on Retina For other t e s t s of v i s u a l a c u i t y , f o v e a l r e t i n a l l o c a t i o n s t y p i c a l l y e x h i b i t maximum s e n s i t i v i t y . As one progresses i n t o the p e r i p h e r y t h r e s h o l d s become e l e v a t e d . G e n e r a l l y speaking t h i s appears to be a l s o the case f o r c o n t r a s t s e n s i t i v i t y to sine wave g r a t i n g p a t t e r n s however t h r e s h o l d s change d i f f e r e n t l y f o r d i f f e r e n t s p a t i a l f r e q u e n c i e s and i t appears that s e n s i t i v i t y i n the v e r t i c a l and h o r i z o n t a l meridians are a l s o unequal. I t i s necessary to p r e f a c e t h i s d i s c u s s i o n of e c c e n t r i c c o n t r a s t s e n s i t i v i t y by n o t i n g that a l l the f o l l o w i n g experiments were c a r r i e d out using e i t h e r TV type monitors or o s c i l l o s c o p e screens of e i t h e r green, white, or b l u i s h (WAD 6500) phosphors. C e r t a i n l y , at l e a s t i n the extreme p e r i p h e r y , s e n s i t i v i t y to chromatic s t i m u l i presented by perimetry d i f f e r s with s t i m u l u s wavelength so i t i s q u i t e p o s s i b l e that a l l these s t i m u l i are not d i r e c t l y comparable. In a d d i t i o n , an e s s e n t i a l l y planar p i c t u r e tube would be analagous to tangent screen p e r i m e t r y . R i j s d i j k e t . a l . (1980) presented g r a t i n g s "...of l i m i t e d dimensions (one g r a t i n g p e r i o d i n the h o r i z o n t a l and one i n the v e r t i c a l d i r e c t i o n ) . . . " ( p . 2 3 6 ) to measure c o n t r a s t s e n s i t i v i t y as a f u n c t i o n of e c c e n t r i c i t y of the s t i m u l u s . However, s i n c e they used g r a t i n g s of .35, .5, 1.4, 2, 4.2, and 6 cyc/deg, t h i s 29 means that t o t a l s timulus s i z e v a r i e d a c r o s s s p a t i a l f r e q u e n c i e s ! The lowest s p a t i a l frequency being a l s o the l a r g e s t t a r g e t s i z e . Larger o v e r a l l t a r g e t area, p e r i m e t r i c a l l y , u s u a l l y r e s u l t s i n a higher p r o b a b i l i t y of d e t e c t i n g the t a r g e t . Given t h i s f a c t i t i s probably unwise to intercompare shape or r a t e of change between the d i f f e r e n t s p a t i a l f r e q u e n c i e s or remark on the d i f f e r e n c e s i n the i s o c o n t r a s t s e n s i t i v i t y curves between d i f f e r e n t s p a t i a l f r e q u e n c i e s . I n t e r e s t i n g l y they found that f o r .5 cyc/deg c o n t r a s t s e n s i t i v i t y was maximal at 0 degree e c c e n t r i c i t y and decreased s t e a d i l y at 2, 4 and 6 degrees along a l l meridians t e s t e d (0-180, 45-225, 90-270, and 135-315 meridians) but that c o n t r a s t s e n s i t i v i t y d i f f e r e d among these meridians. The h i g h e s t c o n t r a s t s e n s i t i v i t y was f o r the 0-180 ,the h o r i z o n t a l m eridian, and poorest for the v e r t i c a l (90-270). They a l s o found that the lower h a l f of the v i s u a l f i e l d was somewhat more s e n s i t i v e than the uppper h a l f as evidenced by the s l i g h t l y higher c o n t r a s t s e n s i t i v i t y v a l u e s found at these e c c e n t r i c i t i e s i n the lower h a l f v i s u a l f i e l d . S i m i l a r f i n d i n g s were obtained f o r the 6 cyc/deg s t i m u l u s . U n f o r t u n a t e l y they d i d not t e s t with s t i m u l i f i n e r than 6 cyc/deg or past 7 degrees i n the v i s u a l f i e l d . Lundh e t . a l . (1983) using a 4.5 by 5 degree stimulus presented at 10 degrees e i t h e r above or below f i x a t i o n a l s o found lower c o n t r a s t s e n s i t i v i t y i n the p e r i p h e r y and a l s o that the lower v i s u a l f i e l d had higher c o n t r a s t s e n s i t i v i t y than the upper. T h i s was most n o t i c e a b l e f o r 2, 3, and 4 cyc/deg. U n f o r t u n a t e l y they d i d not t e s t 6, 8 and 10 cyc/deg c e n t r a l l y so one i s unable to make any comparisons with c e n t r a l c o n t r a s t 30 s e n s i t i v i t y above 4 cyc/deg. Wright and Johnston (1983) compared 2 and 6 cyc/deg, 3.5 by .67 degree g r a t i n g s c e n t r a l l y and out to 12 degree e c c e n t r i c i t y and found that c o n t r a s t s e n s i t i v i t y d e c l i n e d almost l i n e a r l y with e c c e n t r i c i t y but that the slope of t h i s d e c l i n e was d i f f e r e n t f o r each s p a t i a l frequency. The lower s p a t i a l frequency being the l e a s t e f f e c t e d by e c c e n t r i c i t y . Rovamo e t . a l . (1982) used a 3 degree c i r c u l a r white l i g h t g r a t i n g of 0.3 c o n t r a s t and 10 cd/m 2 mean screen luminance and f l a s h e d i t f o r .5 sec. at between 0 and 30 degree e c c e n t r i c i t y . R e s o l u t i o n (that i s , the maximum s p a t i a l frequency d e t e c t a b l e ) decreased r a p i d l y with e c c e n t r i c i t y f a l l i n g from 37 to 7 cyc/deg by the 10 degree e c c e n t r i c i t y on the nasal h a l f meridian of the l e f t v i s u a l f i e l d of one s u b j e c t . The d e c l i n e was l e s s marked (from 7 to 1 cyc/deg) out to 30 degrees. While there i s agreement that c o n t r a s t s e n s i t i v i t y d e creases with e c c e n t r i c i t y and that there are d i f f e r e n c e s i n s e n s i t i v i t y between the upper and lower v i s u a l f i e l d s , not everyone agrees that s e n s i t i v i t y along the h o r i z o n t a l a x i s (0-180 meridian) i s always s u p e r i o r to the v e r t i c a l (90-270). Regan and Beverley (1983) noted that 1 of 3 t e s t e d i n d i v i d u a l ' s c o n t r a s t s e n s i t i v i t y was s u p e r i o r along the v e r t i c a l as opposed to the h o r i z o n t a l m e r i d i a n . T h i s d i f f e r e n c e i s a t t r i b u t e d to i n t e r s u b j e c t d i f f e r e n c e s . P r e c i s e l y what kind i s unknown. Since t e s t i n g was c a r r i e d out using a 3.5 degree t a r g e t (20 cd/m 2 mean p a t t e r n luminance) f o r 2, 4 and 8 cyc/deg without changing t a r g e t s i z e and c e n t r a l p r e s e n t a t i o n , i n a d d i t i o n to p o i n t s out to 24 degree e c c e n t r i c i t y , i t i s p e r m i s s i b l e to compare c o n t r a s t s e n s i t i v i t y a c r o s s a l a r g e p o r t i o n of the 31 r e t i n a f o r these s p a t i a l f r e q u e n c i e s . I t should be noted that the stimulus l i g h t and dark regions were a l t e r n a t e d i n p o s i t i o n (counterphase f l i c k e r ) 16 times per second so t h i s i s not d i r e c t l y comparable to s t i m u l i that are modulated at 0 Hz. In any event t h e i r i s o c o n t r a s t curves f o r 2, 4 and 8 cyc/deg out to 24 degree e c c e n t r i c i t y are reproduced in F i g u r e 7. E v i d e n t l y lower s p a t i a l f r e q u e n c i e s are more d e t e c t a b l e i n the p e r i p h e r a l r e t i n a than those of higher s p a t i a l frequency. 4 c/deg. F i g u r e 7: I s o c o n t r a s t S e n s i t i v i t y Curves f o r V e r t i c a l l y O r i e n t e d S i n e G r a t i n g s of 2, 4, 8 cyc/de F i l l e d c i r c l e s a r e f o r 39 db, f i l l e d diamonds 33 db open diamonds 27 db, f i l e d squares 21 db, and open s q u a r e s 15 db. The db v a l u e s a r e c o n t r a s t s r e l a t i v e 100% c o n t r a s t (0 db i s 100% c o n t r a s t ) . From Regan and B e v e r l e y , 1983, p.756 33 B) C h a r a c t e r i s t i c s of the Stimulus 1) Sine wave versus Square wave It appears that c o n t r a s t s e n s i t i v i t y f o r square wave g r a t i n g s i s s l i g h t l y s u p e r i o r to c o n t r a s t s e n s i t i v i t y for sine wave g r a t i n g s at medium and high s p a t i a l f r e q u e n c i e s and g r e a t l y s u p e r i o r at lower s p a t i a l f r e q u e n c i e s . The magnitude of t h i s d i f f e r e n c e decreases however as mean p a t t e r n luminance i s decreased. (Campbell and Robson, 1968) Contrast s e n s i t i v i t y f o r one subject to s i n e and square wave g r a t i n g s at two mean p a t t e r n luminances i s given i n F i g u r e 8. 2) Temporal Modulation and Shape of Temporal Envelope Temporal modulation of the sine wave p a t t e r n r e s u l t s in an i n c r e a s e in s e n s i t i v i t y f o r the low s p a t i a l f r e q u e n c i e s and has l i t t l e e f f e c t on the f i n e r p a t t e r n s . T h i s e f f e c t has been noted f o r phase r e v e r s a l s as low as 6 Hz. (Sekuler, 1980) and i s c o n s i s t e n t l y r e p o r t e d i n the l i t e r a t u r e . I t appears that t h i s enhancement at low s p a t i a l f r e q u e n c i e s i s r e l a t i v e l y i n v a r i a n t with temporal frequency to approximately 10 Hz. a f t e r which c o n t r a s t s e n s i t i v i t y d e c l i n e s . (Lundh e t . a l . , 1983) I n t e r e s t i n g l y they show maximum temporal r e s o l u t i o n f o r a 4 cyc/deg g r a t i n g (up to 70 Hz.) and cut o f f s f o r 16 cyc/deg at 15 Hz. and 30 Hz. f o r 1 cyc/deg. T h i s i s f o r a 4.5 by 5 degree, 120 cd/m 2 v e r t i c a l g r a t i n g generated on an o s c i l l o s c o p e screen with a green phosphor. Apparently, the type of temporal envelope employed can a l s o e f f e c t the c o n t r a s t s e n s i t i v i t y f u n c t i o n . H i g g i n s e t . a l . (1983) us i n g e i t h e r a r e c t a n g u l a r 5.4 by 5.4 degree or c i r c u l a r 8 1000 100 • u D ° O Q O Q • O ° O O O o - : : „ • • • • • • o o • o • o ° 500 cd/m2 • o 0.05 cd/m2 o 10 o sine wave • square wave • • <fc> o J I I I 11 i n u n i i i 0-1 1 10 Spatial froc|iioncy (c/dog) F i g u r e 8: C o n t r a s t S e n s i t i v i t y F u n c t i o n f o r Square wave and S i n e wave G r a t i n g s at Two Mean P a t t e r n Lum i nances From Campbell and Robson, 1968, p.557 35 degree f i e l d found that a si n e wave temporal e n v e l o p e — t h a t i s the g r a t i n g p a t t e r n ' s luminance at any one po i n t was g r a d u a l l y v a r i e d f o l l o w i n g a smooth sine function--produced a d i f f e r e n t c o n t r a s t s e n s i t i v i t y f u n c t i o n than when a square wave temporal envelope was employed (an abrupt luminance v a r i a t i o n ) . The square waveform r e s u l t e d i n inc r e a s e d s e n s i t i v i t y i n the lowest s p a t i a l frequency and not at any higher s p a t i a l frequency. When d u r a t i o n of stimulus exposure i s v a r i e d c o n t r a s t s e n s i t i v i t y f o r highest s p a t i a l f r e q u e n c i e s appear to be l a r g e l y u n e f f e c t e d . As exposure time i s decreased c o n t r a s t s e n s i t i v i t y f a l l s more so f o r medium s p a t i a l f r e q u e n c i e s but low s p a t i a l f r e q u e n c i e s are a l s o e f f e c t e d . The shape of the c o n t r a s t s e n s i t i v i t y f u n c t i o n becomes f l a t t e r with d e c r e a s i n g exposure time. (Watanabe e t . a l . , 1968) Of course a r e t i n a l l y s t a b i l i z e d g r a t i n g p a t t e r n r e s u l t s i n g r e a t l y reduced c o n t r a s t s e n s i t i v i t y at a l l s p a t i a l f r e q u e n c i e s . ( K e l l y , 1981) For an 8 degree yellow g r a t i n g at l e a s t , the e f f e c t of a s t a b i l i z e d s i n e p a t t e r n can be seen i n F i g u r e 9. 3) G r a t i n g O r i e n t a t i o n There i s general agreement that f o r c e n t r a l l y presented s i n e g r a t i n g s the o r i e n t a t i o n of the stimulus e f f e c t s c o n t r a s t s e n s i t i v i t y . (Watanabe e t . a l . , 1968; Essock, 1982) The ne u r a l mechanism r e s p o n s i b l e f o r t h i s or even i t s l o c a t i o n - - t h a t i s , i s i t p r i m a r i l y a r e t i n a l or c o r t i c a l phenemon f o r example— i s however s t i l l h i g h l y c o n t r o v e r s i a l . S p a t i a l l y tuned c o r t i c a l neurons have been found i n the cat and so many b e l i e v e that t h i s i s the s u i t a b l e n e u r a l s i t e f o r such an e f f e c t (see Coren e t . a l . , 1984 f o r f u r t h e r d i s c u s s i o n ) . Regardless of the u n d e r l y i n g 36 0.25 0.5 1 2 4 8 . F i g u r e 9: C o n t r a s t S e n s i t i v i t y f o r S t a b i l i z e d and U n s t a b i l i z e d S i n e G r a t i n g s ( y e l l o w g r a t i n g s ) From K e l l y . 1981. p.258 37 p h y s i o l o g y , i t appears that t h r e s h o l d s f o r g r a t i n g s with o b l i q u e o r i e n t a t i o n s are e l e v a t e d r e l a t i v e to e i t h e r v e r t i c a l or h o r i z o n t a l o r i e n t a t i o n s . T h i s o r i e n t a t i o n d i f f e r e n c e appears to be maximal f o r the f i n e r p a t t e r n s and appears to be independent of wavelength. At l e a s t f o r white, green and red p a t t e r n s . M i t c h e l l e t . a l . (1967) t e s t e d o r i e n t a t i o n s e n s i t i v i t y u s i ng a l a s e r i n t e r f e r o m e t e r device and found a marked e f f e c t of stimulus o r i e n t a t i o n . The r e s u l t s from one subject are reproduced i n F i g u r e 10. One should note that to a t t a i n these s p a t i a l f r e q u e n c i e s f i e l d s i z e of the t a r g e t was not h e l d constant over c o n d i t i o n s ( v a r i e d from 5 to 11 degrees of subtense) and t h a t d i f f e r e n t s u b j e c t s e x h i b i t e d d i f f e r e n t c o n t r a s t s e n s i t i v i t i e s . One of the three s u b j e c t s f o r example had c o n t r a s t s e n s i t i v i t y to v e r t i c a l g r a t i n g s that was o n l y s l i g h t l y s u p e r i o r to that f o r o b l i q u e o r i e n t a t i o n s and c o n s i d e r a b l y l e s s than f o r h o r i z o n t a l g r a t i n g s . There would appear to be c o n s i d e r a b l e i n t e r s u b j e c t v a r i a b i l i t y i n the magnitude of t h i s e f f e c t . Whether a pronounced "oblique e f f e c t " occurs f o r c o a r s e r p a t t e r n s i s s t i l l i n d i s p u t e . R i j s d i j k e t . a l . (1980) found no e f f e c t at.lower s p a t i a l f r e q u e n c i e s ( l e s s than 6 cyc/deg) while Regan and B e v e r l e y (1983) c l a i m to n o t i c e an e f f e c t of o r i e n t a t i o n f o r a 4 cyc/deg 16 Hz. temporally modulated t a r g e t . One i s l e d to" conclude, however, that no o r i e n t a t i o n e f f e c t o c c u r r e d f o r the 2 cyc/deg g r a t i n g as i t was not r e p o r t e d by them. 4) Presence of Edges i n the Stimulus F i e l d A g r a t i n g p a t t e r n presented to the eye may have l o c a t i o n s 38 > * I 0 0 • - 5 0 CO c : CO o 1 0 ~ 5 13 -TO O 0 4 5 9 0 1 3 5 1 8 0 - / I \ -O r i e n t a t i o n F i g u r e 10: E f f e c t of P a t t e r n O r i e n t a t i o n on the CSF f o r F i v e S p a t i a l F r e q u e n c i e s ( c y c l e s / m i n u t e of a r c ) From M i t c h e l l e t . a l . , 1967, p.247 39 that have higher c o n t r a s t than those of the g r a t i n g s t i m u l i i t s e l f . T h i s i s e s p e c i a l l y n o t i c e a b l e f o r a t a r g e t presented on a dark background as the stimulus edge may be at a high luminance phase of the sine wave r e s u l t i n g i n a marked d i f f e r e n c e between stimulus edge and background. The e f f e c t of sh a r p l y t e r m i n a t i n g a s i n u s o i d a l g r a t i n g was examined by K e l l y (1970). An 8 degree wide by 4 degree high r e c t a n g u l a r s i n u s o i d a l g r a t i n g was tr u n c a t e d on one edge i n one of two ways. The g r a t i n g was e i t h e r terminated when the p e r i o d of the s i n u s o i d was at i t s maximum luminance (the peak of the si n e f u n c t i o n ) or zero edge c o n t r a s t . I n t e r e s t i n g l y c o n t r a s t s e n s i t i v i t y was markedly e f f e c t e d depending upon these c o n d i t i o n s and was not i d e n t i c a l f o r d i f f e r e n t s p a t i a l f r e q u e n c i e s . For the lowest s p a t i a l f r e q u e n c i e s , t e r m i n a t i n g the g r a t i n g f o r maximal edge c o n t r a s t r e s u l t e d in g r e a t l y improved c o n t r a s t s e n s i t i v i t y over the zero edge c o n t r a s t c o n d i t i o n . T h i s enhancement disappeared fo r g r a t i n g s of 1 cyc/deg or f i n e r with the zero edge c o n t r a s t c o n d i t i o n y i e l d i n g s u p e r i o r c o n t r a s t s e n s i t i v i t y up to about 5 cyc/deg a f t e r which no d i f f e r e n c e e x i s t e d between c o n d i t i o n s . The f i n e s t p a t t e r n used was about 12 cyc/deg. T h i s r e s u l t was based upon one s u b j e c t , with n a t u r a l p u p i l s , b i n o c u l a r viewing and 382 cd/m 2 mean luminance. They a l s o note i n p a s s i n g that t h i s e f f e c t i s not observed f o r t a r g e t s l a r g e r than 10 or 15 degrees. T h i s they a t t r i b u t e to nonfoveal t e r m i n a t i o n of a t a r g e t of t h i s s i z e . T h i s e f f e c t i s a l s o f e l t to be l e s s f o r c i r c u l a r versus r e c t a n g u l a r p a t t e r n s . I t appears that the abrupt t e r m i n a t i o n of the p a t t e r n i s the c r u c i a l v a r i a b l e as Van der W i l d t and Waarts (1983) 40 demonstrated that s t i m u l i which v a r i e d i n background luminance but were bounded by sharp, dark bands d i d not d i f f e r a p p r e c i a b l y in terms of c o n t r a s t s e n s i t i v i t y . The luminance p r o f i l e s of four of the s t i m u l i they used are reproduced i n F i g u r e 11. There was no d i f f e r e n c e i n c o n t r a s t s e n s i t i v i t y between stimulus A versus B or f o r stim u l u s C versus D. D i f f e r e n c e s do e x i s t however when one v a r i e s the number of c y c l e s in the stimulus f i e l d and the s i z e of the g r a t i n g . 5) Target S i z e or Number of Pe r i o d s i n the Stimulus F i e l d Campbell and Robson i n t h e i r 1968 paper r e p o r t e d the e f f e c t of v a r y i n g a v a r i e t y of parameters on s p a t i a l c o n t r a s t s e n s i t i v i t y . In order to r e a l i z e s i n e p a t t e r n s of a wide range of s p a t i a l f r e q u e n c i e s , i t was necessary to vary the observer to apparatus d i s t a n c e . The f a r t h e r d i s t a n c e being used to r e a l i z e higher s p a t i a l f r e q u e n c i e s . Even with proper o p t i c a l c o r r e c t i o n f o r both viewing d i s t a n c e s , d i f f e r e n c e s i n c o n t r a s t s e n s i t i v i t y appeared between the two viewing c o n d i t i o n s . In the near c o n d i t i o n (57 cm.), the 10 by 10 cm. screen subtended 10 by 10 degrees while at 285 cm. (the f a r viewing c o n d i t i o n ) the same aperature subtended 2 by 2 degrees. When f i e l d s i z e was reduced to 2 by 2 degrees at 57 cm., the observed d i f f e r e n c e s disappeared. These d i f f e r e n c e s e x i s t e d , i n t h i s p a r t i c u l a r s i t u a t i o n only f o r g r a t i n g s of lower s p a t i a l frequency below about 2 cyc/deg. Those s p a t i a l f r e q u e n c i e s t e s t e d above t h i s - - u p to 10 cyc/deg—were not e f f e c t e d by stimulus subtense. Height of stimulus was v a r i e d s y s t e m a t i c a l l y by Wright (1982). He found that f o r any s p a t i a l frequency there was a l e n g t h above which f u r t h e r i n c r e a s e s i n length caused l i t t l e or no i n c r e a s e in 41 F i g u r e 11: H o r i z o n t a l Luminance P r o f i l e s of S t i m u l i used by Van der W i l d t and Waarts (1903) From Van der W i l d t and Waarts, 1983, p.823 42 c o n t r a s t s e n s i t i v i t y . T h i s c r i t i c a l length v a r i e d f o r each s p a t i a l frequency. In g e n e r a l the lower the s p a t i a l frequency the l a r g e r the c r i t i c a l g r a t i n g l e n g t h . For example t h i s value for 4 cyc/deg was approximately 2 degrees and was 20 minutes f o r 32 cyc/deg. In t h i s p a r t i c u l a r s i t u a t i o n the mean p a t t e r n luminance of the o s c i l l o s c o p e was 100 cd/m2 and the p a t t e r n i s assumed to be 4 degrees in width and was phase re v e r s e d at 0.5 Hz. Howell and Hess (1978) v a r i e d both g r a t i n g width and height and concluded that both i n f l u e n c e d c o n t r a s t s e n s i t i v i t y . They found a c r i t i c a l area f o r each s p a t i a l frequency above which f u r t h e r i n c r e a s e s i n area l e d to r e l a t i v e l y constant c o n t r a s t t h r e s h o l d s . F u r t h e r , t h i s c r i t i c a l area was s m a l l e s t f o r the higher s p a t i a l f r e q u e n c i e s and l a r g e r f o r the c o a r s e r p a t t e r n s (eg. 1 by 1 degree for 10 cyc/deg versus 20 by 20 degrees f o r .5 cyc/deg). Often i n these s t u d i e s t h a t examine f i e l d s i z e and i t s e f f e c t on the CSF, r e s e a r c h e r s g i v e t h e i r r e s u l t s i n terms of the number of p e r i o d s of the g r a t i n g (as opposed to g r a t i n g area) but to manipulate the number of bars i n the stimulus f i e l d — a s was o f t e n done in s t u d i e s of the e f f e c t of width of the g r a t i n g — i t was necessary to vary the s p a t i a l extent of the p a t t e r n i t s e l f . For example, p r e s e n t i n g one g r a t i n g p e r i o d at 10 cyc/deg must r e s u l t i n a s m a l l e r t a r g e t than one p e r i o d with a s p a t i a l frequency of only 1 cyc/deg. The q u e s t i o n a r i s e s whether i t i s the number of p e r i o d s of the g r a t i n g or s p a t i a l extent of the g r a t i n g ( i e . f i e l d s i z e ) t h a t i s i n f l u e n c i n g the CSF or perhaps they are merely d i f f e r e n t t e r m i n o l o g i e s f o r the same 43 phenemon, namely, f i e l d s i z e . T h i s n o t i o n has some appeal given that v a r y i n g stimulus h e i g h t — w h i c h does not e f f e c t the number of p e r i o d s of the g r a t i n g — c l e a r l y i n f l u e n c e s the CSF as long as the height i s l e s s than the above noted c r i t i c a l v a l u e s . 6) Mean Luminance of P a t t e r n Hoekstra e t . a l . (1974) v a r i e d the number of c y c l e s (and of course t h e r e f o r e f i e l d s i z e ) of a 2 cyc/deg g r a t i n g at four d i f f e r e n t mean p a t t e r n luminances (2, 25, 165, and 600 cd/m 2). The e f f e c t of these manipulations on one subject are shown in F i g u r e 12. Larger a t t e n u a t i o n (the Y-axis) i n d i c a t e s l e s s modulation of the si n e p a t t e r n and t h e r e f o r e g r e a t e r s e n s i t i v i t y . As can be seen from t h i s f i g u r e , i n c r e a s i n g mean p a t t e r n luminance r e s u l t s i n grea t e r c o n t r a s t s e n s i t i v i t y f o r t h i s low s p a t i a l frequency. I n t e r e s t i n g l y , the c r i t i c a l v a l u e — the number of c y c l e s above which no i n c r e a s e in c o n t r a s t s e n s i t i v i t y i s r e a l i z e d — c h a n g e s with mean p a t t e r n luminance. In other terminology the small t a r g e t s i z e and high mean p a t t e r n luminance would r e s u l t i n a g l a r e stimulus i f the background was not of the same luminance. U n f o r t u n a t e l y , i n t h i s r e p o r t , no mention of the surround i s given. S t i l l , though, i t appears c l e a r l y that g r e a t e r c o n t r a s t s e n s i t i v i t y occurs with higher mean p a t t e r n luminance. The e f f e c t of mean p a t t e r n luminance on other s p a t i a l f r e q u e n c i e s has been examined by Watanabe e t . a l . (1968), Schade (1956), and Campbell and Robson (1968). Watanabe e t . a l . (1968) t e s t e d CSF to mean p a t t e r n luminances of e i t h e r 171.3, 34.26 or 10.28 cd/m 2, they report t h e i r r e s u l t s i n l i n e s / m i n of arc i n s t e a d of c y c l e s per degree. A t t e n u a t i o n (dB) - / 6 0 0 c d / m 2 1 6 5 c d / m 2 2 5 c d / m 2 2 c d / r m n u m b e r o f c y c l e s n I 5» 10 15 F i g u r e 12: M o d u l a t i o n S e n s i t i v i t y as a F u n c t i o n of the Number of C y c l e s f o r Four Mean P a t t e r n Luminances. Two cyc/deg g r a t i n g o n l y From H o e k s t r a e t . a l . , 1974, p.366 45 [I f they f o l l o w t e l e v i s i o n terminology the l i n e number i s the number of h a l f c y c l e s in a u n i t l e n g t h (which i s minutes of arc h e r e ) . What p r e c i s e l y they meant however i s uncl e a r from t h i s paper.] S t i l l though they found c o n t r a s t s e n s i t i v i t y to be s u p e r i o r f o r hig h s p a t i a l f r e q u e n c i e s at 171.3 cd/m 2 than f o r e i t h e r 34.26 or 10.28 cd/m 2. T h i s d i f f e r e n c e disappears as s p a t i a l frequency decreases however. One would be tempted to conclude based upon t h e i r f i g u r e s i x that there i s no s i g n i f i c a n t d i f f e r e n c e between c o n t r a s t s e n s i t i v i t y to 34.26 or 10.28 cd/m 2 and only between 171.3 and 34.26 (or 10.28) cd/m 2 at s p a t i a l f r e q u e n c i e s above about 1 l i n e / m i n of a r c . Schade, who measured at mean luminances of e i t h e r 1370.4, 137, 13.7, 1.37, 0.137, or 0.01 cd/m 2; noted changes i n s e n s i t i v i t y with mean p a t t e r n luminance. Lower luminance l e v e l s r e s u l t e d i n s h i f t s of s e n s i t i v i t y curves toward c o a r s e r s p a t i a l f r e q u e n c i e s . I t i s d i f f i c u l t , and probably unwise, to be more p r e c i s e i n the exact nature of t h i s change as h i s r e s u l t s were repo r t e d i n terms of a normalized s i n e wave response f a c t o r . F o r t u n a t e l y Campbell and Robson measured the CSF up to 30 cyc/deg at two mean p a t t e r n luminances and re p o r t i n terms of the c o n v e n t i o n a l c o n t r a s t s e n s i t i v i t y measure. U n f o r t u n a t e l y t h i s they d i d f o r only two luminances of 500 and 0.05 cd/m 2. The r e s u l t s of t h i s m anipulation can be seen i n F i g u r e 8. One sees lower c o n t r a s t s e n s i t i v i t y at lower mean luminance and i n a b i l i t y to r e s o l v e higher s p a t i a l f r e q u e n c i e s . I n t e r e s t i n g l y , the magnitude of the l o s s d i m i n i s h e s at the c o a r s e s t g r a t i n g p a t t e r n s . That i s the d i f f e r e n c e between the two curves at .2 cyc/deg i s smaller than f o r example at 2.0 cyc/deg. 46 As s t i l l lower mean p a t t e r n luminances are used the curves p r o g r e s s i v e l y s h i f t toward the lower s p a t i a l f r e q u e n c i e s and c o n t r a s t s e n s i t i v i t y continues to d e c l i n e . I t appears that the e f f e c t of mean p a t t e r n luminance--at l e a s t f o r mean luminances below 1 c d / m 2—can be somewhat o f f s e t by i n c r e a s i n g the angular subtense of the p a t t e r n , (van Meeteren and Vos, 1972) 7) Luminance of Background S u p r i s i n g l y , i t appears that very few s t u d i e s e x i s t that s y s t e m a t i c a l l y vary surround luminance and s i z e of the surround. Most r e s e a r c h e r s when studying s p a t i a l c o n t r a s t s e n s i t i v i t y match the surround to the mean luminance of the g r a t i n g ( o f t e n being c a r e f u l to use the same c o l o u r as the g r a t i n g as w e l l ) . C e r t a i n l y surround luminance can be a c r i t i c a l f a c t o r . R e c a l l , f o r example, K e l l y (1970) who showed the e f f e c t of sharp edges on the CSF. The abrupt r e t i n a l edge produced i s somewhat s i m i l a r to using a surround with other than the same mean luminance of the p a t t e r n . As only one edge of the g r a t i n g was a b r u p t l y terminated however i t i s d i f f i c u l t to apply the f i n d i n g s of t h i s study to v a r i a t i o n s of o v e r a l l surround luminance. Howell and Hess (1978) using an 80 degree wide by v a r i a b l e height stimulus (mean luminance 100 cd/m 2; s p a t i a l frequency 0.1 cyc/deg) found that t u r n i n g o f f the background luminance, versus a background of the same mean luminance as the p a t t e r n , l e d to reduced c o n t r a s t s e n s i t i v i t y u n t i l the g r a t i n g was at l e a s t 30 degrees in height or more. Higher s p a t i a l f r e q u e n c i e s were not t e s t e d . McCann and H a l l (1980) v a r i e d width and luminance of the surround f o r a 1.25 cyc/deg g r a t i n g . A 1.25 by 1.25 degree square c o n t a i n i n g one p e r i o d of a 1.25 cyc/deg s i n e wave was 47 flanked on a l l s i d e s by equal luminance surrounds of e i t h e r 0, .3, 1.2, or 4.7 degrees i n s i z e . In t h i s i n s t a n c e poorest c o n t r a s t s e n s i t i v i t y was recorded when the 9.4 cd/m 2 mean luminance g r a t i n g was surrounded by darkness. The 4.7 degree annular surround l e d to at l e a s t a f o u r - f o l d i n c r e a s e i n c o n t r a s t s e n s i t i v i t y . One assumes some type of luminance and area i n t e r a c t i o n that would e f f e c t the CSF. 8):Colour of P a t t e r n U s u a l l y s i n u s o i d a l g r a t i n g p a t t e r n s are generated on a cathode ray tube. D i f f e r e n t monitors o f t e n vary i n terms of phosphors employed. For example, a P4 phosphor i s w h i t e i s h while a P31 i s green. In a d d i t i o n He-Ne l a s e r i n t e r f e r o m e t e r s are red ( Xd=632.8 nm.). Paper g r a t i n g t e s t s such as the Arden t e s t while on black and white photographic paper, w i l l be e f f e c t e d by whatever c o l o u r the room i l l u m i n a t i o n i s . A l l t h i s d i v e r s i t y i n d i s p l a y wavelength leads to the q u e s t i o n : i s the CSF a f f e c t e d by va r y i n g d i s p l a y c o l o u r ? M e t h o d o l o g i c a l l y the e f f e c t of wavelength on s p a t i a l CSF u s u a l l y f a l l s i n t o one of the f o l l o w i n g c a t e g o r i e s . 1) G r a t i n g of one c o l o u r i s modulated about some mean va l u e . The peaks are b r i g h t e r and the troughs dimmer. (Van Nes and Bouman, 1967; Watanabe e t . a l . , 1968; Zulauf e t . a l . , 1984) 2) B r i g h t n e s s remains constant but p u r i t y i s modulated. The ta r g e t becomes more (the peak of the s i n e wave) and l e s s (the trough of the s i n e wave) s a t u r a t e d . T h i s technique i s o f t e n termed c h r o m a t i c i t y modulation. (Schade, 1958; Van der Horst, 1969; Van der Horst and Bouman, 1969; Granger and H e u r t l e y , 1973; K e l l y , 1981) 48 3) A chromatic g r a t i n g p a t t e r n i s d i s p l a y e d on a chromatic background. ( K e l l y , 1973) Only those experiments employing method 1 w i l l be d i s c u s s e d here as they d i r e c t l y p e r t a i n to the measurement technique employed in the present study, (see Appendix Three) Watanabe e t . a l . (1968) concluded that red and green CSF were e s s e n t i a l l y i d e n t i c a l and that when luminances were matched blue CSF were a l s o s i m i l a r although s l i g h t l y reduced from that of red and green. Van Nes and Bouman (1967) r e p o r t s i m i l a r r e s u l t s but note that as mean p a t t e r n luminance i s decreased, blue e x h i b i t s g r e a t e r c o n t r a s t s e n s i t i v i t y — t h a t i s , the peak s e n s i t i v i t y i s g r e a t e r — t h a n e i t h e r red or green. T h i s d i f f e r e n c e becomes n o t i c e a b l e f o r mean p a t t e r n luminances of l e s s than 0.09 t r o l a n d s . I t was not n o t i c e a b l e at e i t h e r 0.9 or 9 t r o l a n d s . Zulauf e t . a l . (1984) examined s p a t i a l c o n t r a s t s e n s i t i v i t y f o r e i t h e r white, red, green, or blue g r a t i n g s at three stimulus o r i e n t a t i o n s f o r e i t h e r 3, 6, 12, 18, or 24 cyc/deg. The so-c a l l e d o b l i q u e e f f e c t e x i s t e d f o r a l l stimulus wavelengths but appeared l e a s t so f o r blue. Any f u r t h e r d i f f e r e n c e s i n CSF and co l o u r such as CSF f o r the d i f f e r e n t wavelengths by o r i e n t a t i o n were not r e p o r t e d . Mean p a t t e r n luminance was a l s o not r e p o r t e d but given the instrument used--a m o d i f i e d Lotmar r e t i n a l v i s u a l a c u i t y a p p a r a t u s - - i t i s q u i t e l i k e l y t h a t no d i f f e r e n c e s i n CSF to v e r t i c a l l y o r i e n t e d g r a t i n g s a t l e a s t would be noted f o r the d i f f e r e n t wavelengths. 9) Method of Determining T h r e s h o l d The amount of stimulus modulation necessary to evoke a 49 t h r e s h o l d response from the observer i s a f f e c t e d to some extent by how the stimulus c o n t r a s t i s v a r i e d i n time. D i f f e r e n t methods of v a r y i n g stimulus energy have been d e v i s e d and each one appears to y i e l d s l i g h t l y d i f f e r e n t t h r e s h o l d v a l u e s . The f o l l o w i n g methods have been employed. 1) Method of i n c r e a s i n g c o n t r a s t (method of ascending l i m i t s ) . In t h i s task the amplitude of the sine wave i s in c r e a s e d from mean screen luminance u n t i l a g r a t i n g can be de t e c t e d . 2) Method of adjustment. The observer manually a l t e r s c o n t r a s t u n t i l a p o r t i o n of the p a t t e r n can be seen. 3) Bekesy t r a c k i n g procedure. Modulation depth i s i n c r e a s e d u n t i l p a t t e r n i s det e c t e d then modulation depth i s decreased u n t i l the p a t t e r n disappears then modulation depth i s i n c r e a s e d once ag a i n . T h i s s e r i e s of r e v e r s a l s continues f o r some prearranged number of r e p e t i t i o n s . Threshold i s u s u a l l y the mean value of s e v e r a l of these r e v e r s a l s . T h i s i s s i m i l a r to the method of l i m i t s (ascending and descending). 4) Forced-choice procedure. Observers are presented with two s t i m u l i e i t h e r v a r i e d s p a t i a l l y ( i e , one p a t t e r n beside the other) or temporally (one presented a f t e r the o t h e r ) . The 50 observer must decide which was the p a t t e r n . (Vegan and H a l l i d a y , 1982) 5) Method of constant s t i m u l i - a s c e n d i n g . The stimulus i s presented at some modulation, i f not pe r c e i v e d , the stimulus i s removed from s i g h t , i n c r e a s e d in modulation depth by some amount, and then presented again. T h i s c o n t i n u e s u n t i l the s t i m u l u s i s i d e n t i f i e d . Each of these methods appears to have i t s advantages and disadvantages. For example Ginsburg and Cannon (1983) compare the Bekesy t r a c k i n g method with e i t h e r the method of i n c r e a s i n g c o n t r a s t or the method of adjustment and f i n d t h a t the von Bekesy method r e s u l t s i n the l a r g e s t v a r i a b i l i t y w i t h i n each s u b j e c t . The method of i n c r e a s i n g c o n t r a s t was the l e a s t v a r i a b l e . I t appears that the f o r c e d - c h o i c e procedure i s l e s s v a r i a b l e — b y t e s t r e t e s t c o m p a r i s o n — t h a n i s the method of i n c r e a s i n g c o n t r a s t . (Higgins e t . a l . , 1984) Hig g i n s e t . a l . a l s o conclude that these two methods y i e l d e s s e n t i a l l y the same c o n t r a s t s e n s i t i v i t y f u n c t i o n — a l l other parameters being equal--while Ginsburg and Cannon rank them i n terms of maximal c o n t r a s t s e n s i t i v i t y as f o l l o w s : ( h i g h e s t t o lowest) Bekesy, adjustment, and method of i n c r e a s i n g c o n t r a s t . A l l curves were s i m i l a r i n shape but s h i f t e d up or down from one another. I n t e r e s t i n g l y , they p o i n t out that r a t e of c o n t r a s t change i s an important v a r i a b l e that e f f e c t s t h r e s h o l d f o r the method of i n c r e a s i n g c o n t r a s t . The f a s t e r the r a t e of c o n t r a s t change the poorer the c o n t r a s t s e n s i t i v i t y (at l e a s t f o r the 4 51 cyc/deg g r a t i n g they used as the s t i m u l u s ) . T h i s e f f e c t i s f u r t h e r supported by the experiment r e p o r t e d i n Appendix Two: b a s i c a l l y the method of i n c r e a s i n g c o n t r a s t y i e l d e d g r e a t l y reduced c o n t r a s t s e n s i t i v i t y versus the very slow r a t e of c o n t r a s t change i n the method of constant s t i m u l i . I t i s not c l e a r from the one subject t e s t e d whether d i f f e r e n t s p a t i a l f r e q u e n c i e s are d i f f e r e n t l y a f f e c t e d and Ginsburg and Cannon t e s t e d the e f f e c t of p r e s e n t a t i o n time f o r only one s p a t i a l frequency (4 cyc/deg) so t h i s q u e s t i o n remains unanswered at p r e s e n t . One should note that to determine t h r e s h o l d s by the method of constant s t i m u l i r e q u i r e s about 3 times longer than using the method of i n c r e a s i n g c o n t r a s t . 52 V a r i a b l e s that are c h a r a c t e r i s t i c s of the observer as w e l l as m o d i f i c a t i o n s of the stimulus can e f f e c t the c o n t r a s t s e n s i t i v i t y f u n c t i o n . C l e a r l y there are many parameters to c o n s i d e r . While i t may be p o s s i b l e to choose stimulus c o n f i g u r a t i o n s to y i e l d maximally u s e f u l i n f o r m a t i o n about some problem, t h i s v a r i a b i l i t y in methodology renders an attempt to combine r e s u l t s from v a r i o u s r e s e a r c h e r s with t h e i r v a s t l y d i f f e r e n t t o o l s , techniques, and observers somewhat dubious. Even i f the stimulus parameters chosen are not optimum to d e t e c t any group d i f f e r e n c e s , as long as group treatment d i f f e r s by only one v a r i a b l e , i t i s s t i l l p o s s i b l e to conclude something of the e f f e c t of t h i s one v a r i a b l e on the CSF. T h i s b a s i c p r i n c i p l e u n d e r l i e s the examination of the e f f e c t of the age of the observer on the s p a t i a l c o n t r a s t s e n s i t i v i t y f u n c t i o n to f o l l o w . P r i o r t o t h i s however, i t i s i n s t r u c t i v e to d i s c u s s other s t u d i e s in which the e f f e c t of age on the CSF was r e p o r t e d . 53 The E f f e c t of Age of Observer Upon the S p a t i a l Contrast S e n s i t i v i t y F u n c t i o n Evidence from a v a r i e t y of sources i n d i c a t e s that as most i n d i v i d u a l s age, t h e i r v i s u a l system changes. Without commenting on the rate of change through decades of l i f e or the u n d e r l y i n g mechanisms r e s p o n s i b l e f o r these changes, i t i s evident that the average twenty year o l d human's v i s u a l f u n c t i o n d i f f e r s from that of the average s i x t y year o l d . For example, dark a d a p t a t i o n t h r e s h o l d s r i s e , c o l o u r d i s c r i m i n a t i o n becomes poorer, c r i t i c a l f l i c k e r frequency d i m i n i s h e s , primary geometric i l l u s i o n s i n c r e a s e i n magnitude, embedded f i g u r e s are more d i f f i c u l t to d e t e c t , and S n e l l e n a c u i t y i s poorer i n the o l d e r group. T h i s l a s t measure--the r e c o g n i t i o n of optotypes of d i m i n i s h i n g s i z e — i s viewed by some as an incomplete d e s c r i p t i o n of an i n d i v i d u a l ' s v i s u a l a c u i t y s i n c e the task u t i l i z e s only s t i m u l i at 100% p h y s i c a l c o n t r a s t . A more complete measure i s f e l t to be what i s o f t e n termed s p a t i a l c o n t r a s t s e n s i t i v i t y and the r e s u l t a n t c o n t r a s t s e n s i t i v i t y f u n c t i o n (CSF). I t i s p o s s i b l e , t h e r e f o r e , that the use of t h i s technique to study changes i n v i s u a l f u n c t i o n with i n c r e a s i n g age may prove more r e v e a l i n g than the use of S n e l l e n a c u i t y . S e v e r a l i n d i v i d u a l s have examined the e f f e c t of ageing on the human v i s u a l system by t e s t i n g the c o n t r a s t s e n s i t i v i t y of i n d i v i d u a l s of v a r i o u s ages to g r a t i n g s with a s p a t i a l luminance p r o f i l e that v a r i e s s i n u s o i d a l l y . U n f o r t u n a t e l y there i s not u n i v e r s a l agreement on the e f f e c t of age upon the CSF. I f one c o u l d a r t i f i c a l l y group s p a t i a l f r e q u e n c i e s i n t o low, medium, and high ranges, the "age" s t u d i e s that are 54 r e p o r t e d i n the l i t e r a t u r e a l l would agree that c o n t r a s t s e n s i t i v i t y i n the medium range (apx. 4 cyc/deg) i s poorer f o r the o l d e r i n d i v i d u a l s . For the other two ranges, however; c o n c l u s i o n s vary. McGrath and M o r r i s o n (1981), Skalka (1984) and Ross e t . a l . (1985) a l l - found a r e d u c t i o n in c o n t r a s t s e n s i t i v i t y at a l l s p a t i a l f r e q u e n c i e s t e s t e d for the o l d e r r e l a t i v e to the younger group. Others r e p o r t that at high s p a t i a l f r e q u e n c i e s c o n t r a s t s e n s i t i v i t y i s depressed ( i e . must have greater p h y s i c a l c o n t r a s t ) i n the o l d e r group r e l a t i v e to the younger and that the lower s p a t i a l f r e q u e n c i e s are r e l a t i v e l y u n e f f e c t e d . (Arundale, 1978; D e r e f e l d t , Lennerstrand, and Lundh, 1979; Sekuler and Owsley, 1982; Owsley, Sekuler and Siemsen, 1983) Sekuler, Hutman, and Owsley (1980) and Sekuler and Hutman (1980) r e p o r t the r e v e r s e . Their o l d e r age group's c o n t r a s t s e n s i t i v i t y was depressed in the low and not the h i g h range r e l a t i v e to the younger group. R e p r e s e n t a t i v e c o n t r a s t s e n s i t i v i t y f u n c t i o n s from s e l e c t e d s t u d i e s can be seen i n F i g u r e 13 A and B. I t would be very b e n e f i c i a l i f one were able to adequately account f o r the l a c k of agreement between v a r i o u s s t u d i e s . C e r t a i n l y , the v a r i a b l e r e s u l t s o b t a i n e d must be a f a c t o r of some, one, or a l l of the f o l l o w i n g p o s s i b i l i t i e s . Ross e t . a l . (1985) as well as the data p r o v i d e d by Skalka i n h i s 1984 l e t t e r i n d i c a t e that o l d e r s u b j e c t s e x h i b i t more v a r i a b l e c o n t r a s t t h r e s h o l d s than do younger s u b j e c t s . That i s , a group of i n d i v i d u a l s say i n t h e i r 6th decade of l i f e would have a g r e a t e r range of t h r e s h o l d s c o r e s than would a group 55 From: Ross, C larke and Bron, 1985, p. 53 top: 20-30 y r s . bottom: 50-87 y r s . — 1 — i . i • 0.45 0.95 2.88 6.70 12.50 19.25 From: Arunda le, 1978, p.214 From: Lundh, Len-nerst rand and D e r e f e l d t , 1983, p.683 •it 1 1 1 1 1 1 1 0.5 1.0 20 40 10 20 40 Spatial frequency (cycles/degree) F i g u r e 13: C o n t r a s t S e n s i t i v i t y F u n c t i o n s from V a r i o u s "Age" S t u d i e s 56 From: Sekuler and Hutman, 1980, p.694 socH 2 1 1 1 1 1 1 0.3 I 2 4 8 16 S p a t i a l F r e q u e n c y (c/d) Figure 13B From: Sekuler and Owsley, 1982, p.190 57 comprised of i n d i v i d u a l s i n t h e i r 2nd decade of l i f e . T h i s means that t e s t i n g only a few i n d i v i d u a l s of o l d e r ages may more l i k e l y r e s u l t i n o b t a i n i n g a f i n d i n g based upon an - u n r e p r e s e n t a t i v e sample. Such a phenomenon i s l e s s l i k e l y to occur when t e s t i n g younger i n d i v i d u a l s . Other i n d i v i d u a l s have reached s i m i l a r c o n c l u s i o n s . For example Sekuler and Owsley (1982) mentioned t h a t : ...Sample s i z e s i n the e a r l i e r work, e s p e c i a l l y f o r the o l d e r age ranges, were q u i t e s m a l l , making i t d i f f i c u l t to determine how p e r v a s i v e changes i n c o n t r a s t s e n s i t i v i t y a c t u a l l y are. S u b s t a n t i a l i n d i v i d u a l d i f f e r e n c e s i n c o n t r a s t s e n s i t i v i t y render i n f e r e n c e s from very small samples r i s k y , (p.187) The number of observers t e s t e d i n each study i s given i n Table Other e x p l a n a t i o n s are based upon the sampling techniques themselves as opposed to the number of s u b j e c t s s e l e c t e d . Sekuler and h i s co-authors o f f e r e d the f o l l o w i n g v i s a v i s the d i f f e r e n t r e s u l t s reported between t h e i r 1980 and 1982/1983 papers. In the e a r l i e r study (1980): A l l observers had good a c u i t y , 20/30 or b e t t e r . Older observers had decreased s e n s i t i v i t y at low and intermediate f r e q u e n c i e s compared to younger obse r v e r s , but had s i m i l a r s e n s i t i v i t y at 16 cyc/deg the highest frequency t e s t e d . S i m i l a r i t y at high f r e q u e n c i e s f o r the two age groups i s not r e a l l y s u r p r i s i n g s i n c e the two groups were very s i m i l a r i n t h e i r a c u i t y l e v e l s . I f o l d e r s u b j e c t s had not been pre-screened fo r good a c u i t y , i n d i v i d u a l s having a c u i t y worse than 20/30 (not uncommon f o r t h i s age range) would have been i n c l u d e d i n the sample. Under these circumstances, high frequency s e n s i t i v i t y i n the o l d e r group would most l i k e l y have been impaired r e l a t i v e to the younger group. (Owsley, Sekuler and Siemsen, 1983, p. 690) T h i s of course i m p l i e s that s e n s i t i v i t y would then have 58 T a b l e 3: S t i m u l u s and O b s e r v e r P a r a m e t e r s i n "Age" S t u d i e s S t i m u l u s Parameters O b s e r v e r s R e f e r e n c e How g e n e r a t e d S t i m u l u s S i z e Mean Background S p a t i a l f r e q u e n c i e s t e s t e d Thresho1 a Tempora1 Ages Examined Number C r i t e r i a F o r I n c l u s i o n / G e n e r a l Comments Pat t e r n I n t e n s i t y Cr i t e r i a Modu1 a t i on Lum i nance • A r u n d a l e , 1978 t e l e v i s i o n 18' by 15' 100 cd/m' not g i v e n 0.25, .5, 1, 2. mean of 5 1 e y e / s e c . Mean Eyes mon i t o r o r 6' by 5' 4. 8. 16.28 c y c / d e g d e s c e n d i ng ( p h a s e 8-15 y r s . 13 3 -no o b s e r v a b l e p a t h o l o g y (P4 p h o s p h o r ) t r i a l s r e v e r s a 1 ) 18-39 y r s . 23 25 -wore c o r r e c t i v e l e n s e s 45-66 y r s . 58 5 -monocular v i e w i n g D e r e f e l d t e t . a l . , 1979 o s c i 1 1 o s c o p e 4.5' by 5' 120 cd/m' 20 cd/m' from 0.5-40 c y c / d e g 2 a s c e n d i n g no o b s e r v e r s (P31) 19 s p a t i a l f r e q . t r i a l s 6-10 y r s . 10 - a l l had S n e l l e n v . a . o f 1.0 o r b e t t e r 20-40 y r s . 12 -over 60 group g i v e n a d d i t i o n a l +.5 s p h e r e >60 y r s . 1 1 -monocular v i e w i n g S e k u l e r e t . a l . , 1980 S e k u l e r and Hutman, 1980 c a t h o d e r a y 4.5' by 5.5" 55 cd/m' same 0.5, 1 , 2 . Bekesy 0.3 Hz. and 18.5 25 - b e s t c o r r e c t e d S n e l l e n v . a . 20/20 ( u s e d same d a t a ) tube ( c o l o u r 4, 8. 16 c y c / d e g t r a c k i ng S.O Hz. and 73 . 2 9 - b e s t c o r r e c t e d S n e l l e n v . a . 20/24 matched) -monocular v i e w i n g McGrath and M o r r i s o n , 1981 o s c i 1 1 o s c o p e 1.7' or 5 cd/m ! between 2 0.33 t o 40 mean o f from 4 no 5-94 y r s . 66 -some r e q u i r e d a d d i t i o n a l c o r r e c t i v e l e n s e s 5.1' and 4 l u x c y c / d e g t o 8 a s c e n d i n g t r i a l s S e k u l e r and Owsley. 1982 no b e s t c o r r e c t e d a c u i t v (M.A.R.) Owsley e t . a 1 . , 1933 19-28 y r s . 22 12 0. 63 ( u s e d same d a t a ) t e 1 e v i s i on 4.2" by 5 . 5' 103 cd/m' 2 cd/m' 0.5, 1.2. Von 8 e k e s y 31-37 y r s . | 33 6 0.79 d i s p l a y 4. 8. 16 c y c / d e g t r a c k i ng 41-48 y r s . I 44 8 0. 78 g e o m e t r i c mean 50-58 y r s . I 54 5 1 .07 of e i g h t 60-69 y r s . 66 18 1 . 27 r e v e r s a 1 s 70-79 y r s . 74 28 1 . 38 80-87 y r s . 82 14 1 . 82 -monocular v i e w i n g S k a l k a . 1982. 1984 Arden not g i v e n not g i v e n .2. .4, .8. 1.6 f i r s t d e t e c t eyes p l a t e s 3.2, 6.4 cy c / d e g p a t t e r n as no 2nd and 3 r d deca d e s 92 -no o b s e r v a b l e p a t h o l o g y v a r i a b l e c o n t - 6 t h decade 32 -monocular v i e w i n g r a s t p i a t e i s u n c o v e r e d Ross e t . a l . . 1985 o s c i 1 1 o s c o p e 30 cm. by 20 300 cd/m' not g i v e n 0.4. .95. 2.88 6.73. d o u b l e s t a i r - o b s e r v e r s cm. viewed a t 12.70. 19.23 c y c / d e g c a s e t h e n no 20-30 y r s . 17 -no o b s e r v a b l e p a t h o l o g y 280 cm. s i n g l e s t a i r - 50-87 y r s . 53 - S n e l l e n v . a . of 6/9 or b e t t e r c a s e mean o f -no o p t i c a l c o r r e c t i o n >±6 d i o p t e r s t h r e e r e v e r s a l s > - b i n o c u l a r v i e w i n g 59 been reduced at a l l s p a t i a l f r e q u e n c i e s while t h e i r 1983 paper shows r e d u c t i o n only at the intermediate and high s p a t i a l frequenc i e s . There i s l i t t l e doubt that s e l e c t i o n of s u b j e c t s — e s p e c i a l l y f o r the o l d e r age g r o u p — c a n g r e a t l y i n f l u e n c e the r e s u l t a n t CSF. I t has a l r e a d y been shown that o c u l a r pathology w i l l change the CSF (see p.19-22). C a r e f u l screening f o r o c u l a r d i s e a s e — s o m e types of which are more p r e v a l e n t i n the o l d e r i n d i v i d u a l s — m u s t be done. V a r i o u s p r e - r e c e p t o r a l f a c t o r s must a l s o be c o n s i d e r e d and h e l d constant i f one wishes to make some type of statement on the e f f e c t of aging independently of, f o r example, i n c r e a s e d l e n t i c u l a r or c o r n e a l o p a c i t y or changes in the r e s o l v i n g power of the o p t i c a l components of the eye i t s e l f . The c h o i c e of a s u i t a b l e o p t i c a l c o r r e c t i o n is' an important c o n s i d e r a t i o n as c o n t r a s t s e n s i t i v i t y to high s p a t i a l f r e q u e n c i e s viewed on a cathode ray tube (CRT) i s reputedly h i g h l y dependent on the r e f r a c t i v e s t a t e of the eye. R e c a l l that Campbell and Green (1965) demonstrated that v a r y i n g o p t i c a l c o r r e c t i o n from the optimum decreases c o n t r a s t s e n s i t i v i t y at higher s p a t i a l f r e q u e n c i e s and that low s p a t i a l f r e q u e n c i e s are l e s s e f f e c t e d . In some s t u d i e s observers were c a r e f u l l y r e f r a c t e d and given t h e i r optimum c o r r e c t i o n which was u s u a l l y d e f i n e d i n terms of maximum S n e l l e n a c u i t y . Others, however, o v e r c o r r e c t the o l d e r age groups as one would, say, i n a p e r i m e t r i c t e s t (eg. D e r e f e l d t e t . a l . , 1979) In a d d i t i o n to p r o p e r l y r e f r a c t i n g s u b j e c t s f o r the t e s t d i s t a n c e , other p r e r e c e p t o r a l f a c t o r s d i f f e r e n t i a l l y e f f e c t the CSF of v a r i o u s age groups. The c r y s t a l l i n e l e n s becomes more 60 opaque with aging. T h i s leads to decreased r e t i n a l i l l u m i n a n c e and i n some in s t a n c e s would be s i m i l a r to viewing the g r a t i n g p a t t e r n at a lower mean screen luminance and c o u l d cause the noted l o s s to high s p a t i a l frequency g r a t i n g p a t t e r n s of o l d e r s u b j e c t s r e l a t i v e to the younger i n d i v i d u a l s . The amount to which t h i s f a c t o r i s r e s p o n s i b l e f o r change in the CSF (versus any u n d e r l y i n g n e u r o l o g i c a l d e f i c i t s ) was assessed by Owsley e t . a l . (1983). They attempted to simulate decreased r e t i n a l i l l u m i n a n c e by having a group of young s u b j e c t s view the g r a t i n g p a t t e r n s through a p p r o p r i a t e n e u t r a l d e n s i t y f i l t e r s . They conclude: ....that when r e t i n a l i l l u m i n a n c e i s roughly e q u a l i z e d f o r 20-yr-olds and 60-yr-olds, the s e n s i t i v i t y d i f f e r e n c e between the two age groups i s minimized. The r e s i d u a l d i f f e r e n c e between o l d and young i s non-s i g n i f i c a n t at 4 and 8 c/deg, but approaches s i g n i f i c a n c e at 16 c/deg....It appears, then, that a s i g n i f i c a n t p o r t i o n of the s e n s i t i v i t y l o s s at intermediate and high s p a t i a l f r e q u e n c i e s i s a t t r i b u t a b l e to a r e t i n a l i l l u m i n a n c e r e d u c t i o n i n the aged eye. (p.696) T h i s c o n c l u s i o n , u n f o r t u n a t e l y , r e s t s upon t h e i r numerical c a l c u l a t i o n s f o r r e t i n a l i l l u m i n a n c e i n young and o l d i n d i v i d u a l s . F u r t h e r , i t i s based upon values d e r i v e d from e n t i r e l y d i f f e r e n t i n d i v i d u a l s than the ones used in t h e i r study. One would l i k e to be more p r e c i s e to determine whether decreased r e t i n a l i l l u m i n a n c e i s mainly r e s p o n s i b l e f o r the r e s u l t i n g changes i n the CSF between i n d i v i d u a l s separated on the age continuum. There appears to be no manipulation of the stimulus that w i l l allow one to t e s t the CSF independently of l e n t i c u l a r o p a c i t y . A l l that one can do i s to s e l e c t i n d i v i d u a l s who s t i l l have c l e a r o p t i c a l media. D i f f e r e n t a l r e f r a c t i v e p r o p e r t i e s of the o p t i c s of the eye can however be e q u a l i z e d by 61 the use of a l a s e r i n t e r f e r o m e t r i c d e v i c e . T h i s technique and the apparatus used i n the age study conducted here are d i s c u s s e d on pages 112 to 113. In a d d i t i o n to p o t e n t i a l d i f f e r e n c e s i n the s u b j e c t s s e l e c t e d f o r the v a r i o u s s t u d i e s of aging and the CSF i t i s evid e n t that stimulus c o n d i t i o n s were not i d e n t i c a l across s t u d i e s . The v a r i o u s stimulus parameters chosen in these s t u d i e s are given i n Table 3. I t i s evident from the p r i o r d i s c u s s i o n of v a r i a t i o n s of stimulus parameters and t h e i r a b i l i t y to e f f e c t the CSF that the reason f o r d i s c r e p a n c i e s between the v a r i o u s age s t u d i e s may p a r t l y , or e n t i r e l y , l i e i n the ch o i c e of sti m u l u s parameters. Perhaps f o r some parameters of the stimulus no d i f f e r e n c e s were observed simply because f o r that p a r t i c u l a r group of stimulus v a r i a b l e s o l d e r and younger observers r e a l l y do not d i f f e r i n t h e i r c o n t r a s t s e n s i t i v i t y f o r that s p a t i a l frequency. P r e c i s e l y what v a r i a t i o n s i n methodology are the cause f o r the d i f f e r e n c e s noted between s t u d i e s i s not d i r e c t l y obvious from an examination of the r e p o r t e d methods u t i l i z e d . T h i s l a c k of c l a r i t y may be due to the f a c t that s u b j e c t s and c r i t e r i a f o r su b j e c t s e l e c t i o n a l s o v a r i e d from study to study. It i s d i f f i c u l t , of course, to study the e f f e c t of one v a r i a b l e when other v a r i a b l e s , the e f f e c t s of which are not known, are a l s o v a r y i n g . I t i s most l i k e l y t h a t the e f f e c t of v a r i o u s s t i m u l u s manipulations should be s e t t l e d not by s p e c u l a t i o n but s e t t l e d by experimentation. An e x p l a n a t i o n of any d i f f e r e n c e s i n c o n t r a s t s e n s i t i v i t y with age f a l l i n t o a few c a t e g o r i e s : 1) p r e r e c e p t o r a l , 2 ) n e u r a l : a n a t o m i c a l / f u n c t i o n a l and 3) response b i a s . 62 H o p e f u l l y i t i s a l r e a d y c l e a r the e f f e c t that d i f f e r e n t p r e r e c e p t o r a l s t a t e s can have upon the CSF. P o s s i b l e d i f f e r e n c e s i n n e u r a l q u a l i t y , q u a n t i t y , and s e l e c t i v e l o s s e s are c o n s i d e r e d i n the D i s c u s s i o n s e c t i o n (p. 88-97). The p o s s i b i l i t y that o l d e r observers have a d i f f e r e n t response c r i t e r i a than t h e i r younger c o u n t e r p a r t s was f u l l y examined by Hutman and Sekuler (1980) who t e s t e d two groups of observers of d i f f e r e n t mean ages on a S i g n a l D e t e c t i o n type task.-Observers i n each group (group 1 mean age 18.4 years; group 2 mean age 73 years) were t e s t e d at a constant amount above t h e i r i n d i v i d u a l t h r e s h o l d value so that d i f f e r e n t i a l s i g n a l d e t e c t a b i l i t y would not be a f a c t o r . They were asked to r a t e the 200 p r e s e n t a t i o n s of e i t h e r s i g n a l present (at 1.25 times i n d i v i d u a l c o n t r a s t t h r e s h o l d ) or absent (0 c o n t r a s t c o n d i t i o n ) f o r the 1 cyc/deg n o n - f l i c k e r i n g g r a t i n g on a 6 p o i n t r a t i n g s c a l e . T h i s s c a l e ranged from 1: there p o s i t i v e l y were bars on the screen; to 6: there p o s i t i v e l y were not bars on the s c r e e n . The number of responses that f e l l i n a p a r t i c u l a r category f o r the s i g n a l present and absent c o n d i t i o n s was then used to determine one of three measures. P(A)--the measure of d e t e c t a b i l i t y was d e r i v e d from the Receiver Operating C h a r a c t e r i s t i c Curve. No d i f f e r e n c e s between the two age groups was found on t h i s measure as was to be expected s i n c e each i n d i v i d u a l was shown a st i m u l u s i n the s i g n a l present c o n d i t i o n that was above t h e i r c o n t r a s t t h r e s h o l d . T h e i r two measures of c r i t e r i o n were termed "B" and "C" and were d e r i v e d as f o l l o w s . "B i s the numerical category on the r a t i n g s c a l e at which an i n d i v i d u a l i s e q u a l l y disposed to say 63 that a g r a t i n g had been presented and to say that no g r a t i n g had been presented. Higher B values i n d i c a t e a tendency to deny that a g r a t i n g had been presented." (p.702) No d i f f e r e n c e was found on t h i s measure between groups e i t h e r . L a s t l y the "C" measure was the r e c i p r o c a l of the s e m i - i n t e r q u a r t i l e range of an observer's r a t i n g s . "For observers who are unbiased a c c o r d i n g to the other measures of c r i t e r i o n , B, l a r g e r values of C i n d i c a t e i n c r e a s i n g r e l u c t a n c e to use extreme c a t e g o r i e s . For example, a r e a l l y c a u t i o u s observer might use only the two c a t e g o r i e s s i g n i f y i n g l e a s t confidence ("3" and "4") and would have C=2.0; an i n c a u t i o u s observer might use only c a t e g o r i e s s i g n i f y i n g g r e a t e s t confidence ("1" and "6") and would have C=.4." (p.703) On t h i s l a s t measure as w e l l they found no s i g n i f i c a n t d i f f e r e n c e s between the two groups when viewing the s t a t i c g r a t i n g p a t t e r n . 64 It i s b e l i e v e d that with 1) c a r e f u l s u b j e c t s e l e c t i o n to e l i m i n a t e o c u l a r pathology and l e n t i c u l a r o p a c i t y as well as p u p i l l a r y d i l a t i o n to equate p u p i l s i z e which i s o f t e n smaller in the olde r age group at the luminance l e v e l t e s t e d in t h i s study, 2) the n u l l i f i c a t i o n of r e f r a c t i v e c o r r e c t i o n by the l a s e r i n t e r f e r o m e t r i c d e v i c e (see Appendix Three) and t e s t i n g only i n d i v i d u a l s with l e s s than ±10 d i o p t e r s r e f r a c t i v e e r r o r , and 3) a s u f f i c i e n t number of observers t o c o n s t i t u t e a r e p r e s e n t a t i v e sample of o l d and young o b s e r v e r s , that one w i l l be able to examine the CSF and be reasonably c o n f i d e n t that any noted changes are not p r i m a r i l y due to p r e r e c e p t o r a l d i f f e r e n c e s between the young and aged eye. S p e c i f i c a l l y , then, i n t e r g r o u p comparisons of each s p a t i a l frequency should r e v e a l some d i f f e r e n t i a l s e n s i t i v i t y between the young and o l d groups. The exact nature of t h i s d i f f e r e n c e i s not c l e a r due to the many c o n f l i c t i n g r e p o r t s from previous r e s e a r c h e r s . A d d i t i o n a l l y , i t i s expected that a comparison of the CSF between i n d i v i d u a l s of d i f f e r e n t gender should r e v e a l no s i g n i f i c a n t d i f f e r e n c e s . 65 Method Subjec t s Fourteen male and fourteen female Caucasian s u b j e c t s between the ages of 18-25 years i n c l u s i v e c o n s t i t u t e d the younger age group. Of these, seventeen (5 male and 12 female) were randomly s e l e c t e d to be compared to a group of seventeen o l d e r i n d i v i d u a l s (5 male and 12 female) between ages 51-81 years i n c l u s i v e . A l l of the o l d e r i n d i v i d u a l s and f i v e of the younger group were o r i g i n a l l y seen i n the eye c l i n i c at U.B.C. f o r a r e g u l a r eye examination and r e f r a c t i o n . They were asked to p a r t i c i p a t e in the experiment by the c l i n i c r e c e p t i o n i s t or a t t e n d i n g p h y s i c i a n i f the eye examination proved u n e v e n t f u l . The 23 remaining younger s u b j e c t s were v o l u n t e e r s r e c r u i t e d from s i g n -up sheets l o c a t e d i n the Psychology b u i l d i n g on campus. No money or course c r e d i t were given to anyone p a r t i c i p a t i n g . Procedure The eye to be used of each s u b j e c t was randomly chosen .prior to t h e i r s c h e d u l i n g f o r t e s t i n g . Once a sub j e c t a r r i v e d i n the c l i n i c , they were taken to an examination room and were given a consent form to sign (see Appendix Four) and were asked fo r t h e i r f u l l name, address, age, h i s t o r y of o c u l a r pathology and any q u e s t i o n s that they might have. No s u b j e c t s r e f u s e d to p a r t i c i p a t e at any time during the experiment. When the consent form had been signed, the eye to be t e s t e d was r e f r a c t e d i n the standard manner, then examined f o r any o c u l a r pathology. I n t r a o c u l a r p r e s s u r e was then recorded. I f the 66 fundus, l e n s , cornea and v i t r e o u s appeared normal and p r e s s u r e s were not e l e v a t e d , the subject was d i l a t e d with 1/2% M y d r i a c y l and returned to the w a i t i n g room u n t i l the drop caused p u p i l l a r y d i l a t i o n . A f t e r approximately 15 minutes, the c o n t r a s t s e n s i t i v i t y t e s t i n g began. The s u b j e c t was then l e d to another room and seated at the Randwal l a s e r i n t e r f e r o m e t e r . P u p i l diameter was recorded and then the c o n t r a s t s e n s i t i v i t y t e s t i n g was e x p l a i n e d . A f t e r each su b j e c t was f a m i l i a r i z e d with the t e s t , t e s t i n g commenced at 15 cyc/deg--the f i n e s t g r a t i n g p r e s e n t e d — a n d proceeded in order through the intermediate s p a t i a l f r e q u e n c i e s to the c o a r s e s t . T e s t i n g d u r a t i o n was noted and the s u b j e c t was thanked and any q u e s t i o n s answered. At each s p a t i a l frequency the f o l l o w i n g procedure was used: s t a r t i n g at the 0.01 c o n t r a s t s e t t i n g , the c o n t r a s t was i n c r e a s e d u n t i l the s u b j e c t c o u l d j u s t d e t e c t the g r a t i n g p a t t e r n with i t s v e r t i c a l l y o r i e n t e d s i n u s o i d a l l y modulated luminance p r o f i l e . T h i s value was recorded as one ascending t r i a l t h r e s h o l d . The t e s t l i g h t was moved out of the s u b j e c t ' s view and c o n t r a s t was i n c r e a s e d above t h i s t h r e s h o l d v a l u e . The p a t t e r n was again shown to the s u b j e c t and as p h y s i c a l c o n t r a s t was decreased asked to s i g n i f y - a g a i n by tapping the t a b l e — w h e n i t was no longer p o s s i b l e to see the "fuzzy bar p a t t e r n " anymore. T h i s was a descending t r i a l . These a l t e r n a t i n g ascending and descending t r i a l s were c a r r i e d out u n t i l f i v e of each were recorded at each s p a t i a l frequency t e s t e d . The seven s p a t i a l f r e q u e n c i e s used were 15, 10, 7.5, 6, 3, 1.5, and .75 cyc/deg. On the Randwal Model 33Y t h i s corresponds 67 to a S n e l l e n n o t a t i o n of 40, 60, 80, 100, 200, 400, and 800 r e s p e c t i v e l y (that i s 20/40, 20/60, e t c . ) . The mean p a t t e r n luminance was 3.5 cd/m 2 and remained constant as modulation depth was v a r i e d . T h i s measurement was taken by f o c u s i n g the 20' f i e l d of a P r i t c h a r d 1980A-PL photometer at 1.2 m. lens to o b j e c t d i s t a n c e and a d j u s t i n g focus u n t i l a c l e a r image of the p a t t e r n s t r i p e s was obt a i n e d . Background luminance was 0.10 cd/m 2 at the observer's eye. The t h r e s h o l d c o n t r a s t value was recorded from the d i a l on the 33Y f o r each of the 5 ascending and 5 descending t r i a l s at each of the seven s p a t i a l f r e q u e n c i e s . A computer program was w r i t t e n to transform the c o n t r a s t t h r e s h o l d values as f o l l o w s . For each su b j e c t the f o l l o w i n g values were d e r i v e d from t h e i r c o n t r a s t t h r e s h o l d v a l u e s : 1) Mean c o n t r a s t t h r e s h o l d for ascending t r i a l s . 2) Mean c o n t r a s t t h r e s h o l d f o r descending t r i a l s . 3) . Mean c o n t r a s t t h r e s h o l d f o r both methods t o g e t h e r . The computer program computed these means as w e l l as t h e i r standard d e v i a t i o n s (which i n d i c a t e s i n t h i s i n s t a n c e the v a r i a b i l i t y of the s u b j e c t ' s t h r e s h o l d responses) and then converted the t h r e s h o l d means i n t o c o n t r a s t s e n s i t i v i t y values for each s p a t i a l frequency by the f o l l o w i n g formula: ( 1/contrast t h r e s h o l d ) * 100. Then geometric mean scores were c a l c u l a t e d by the computer program f o r ascending, descending, and both methods f o r each i n d i v i d u a l at each s p a t i a l frequency where: geoMean= nthsquareroot of (X1*X2*X3...Xn) and n=number of measures. Each geometric mean score was c o r r e c t to at l e a s t the seventh decimal 68 p l a c e . C o n t r a s t s e n s i t i v i t y was c a l c u l a t e d as above. T h i s meant that f o r each i n d i v i d u a l the f o l l o w i n g measures were o b t a i n e d at each s p a t i a l frequency: A r i t h m e t r i c means c o n t r a s t t h r e s h o l d ascending c o n t r a s t t h r e s h o l d descending c o n t r a s t t h r e s h o l d both S.D. of t h r e s h o l d ascending S.D. of t h r e s h o l d descending c o n t r a s t s e n s i t i v i t y ascending c o n t r a s t s e n s i t i v i t y descending c o n t r a s t s e n s i t i v i t y both Geometric means c o n t r a s t t h r e s h o l d ascending c o n t r a s t t h r e s h o l d descending c o n t r a s t t h r e s h o l d both c o n t r a s t s e n s i t i v i t y ascending c o n t r a s t s e n s i t i v i t y descending c o n t r a s t s e n s i t i v i t y both Group performance was compared on s e v e r a l of these measures. 69 R e s u l t s Comparison of the 14 younger male and 14 younger female s u b j e c t s by T - t e s t s r e v e a l e d no s i g n i f i c a n t d i f f e r e n c e s between the sexes on age, r e f r a c t i v e c o r r e c t i o n (sphere, c y l i n d e r and a x i s ) , best c o r r e c t e d S n e l l e n a c u i t y , diameter of d i l a t e d p u p i l and i n t r a o c u l a r p r e s s u r e . No T - s t a t i s t i c s were s i g n i f i c a n t at even the .25 l e v e l . Although f o r t h i s sample, the males e x h i b i t e d g r e a t e r c o n t r a s t s e n s i t i v i t y at a l l s p a t i a l f r e q u e n c i e s , one-way a n a l y s i s of v a r i a n c e on a r i t h m e t i c mean c o n t r a s t s e n s i t i v i t y s c o r e s fo r each i n d i v i d u a l f o r e i t h e r the 5 ascending (F(1,9)=.242), 5 descending (F(1,9)=.681), or combined (F=1,9)=.561) t r i a l s i n d i c a t e d no s i g n i f i c a n t d i f f e r e n c e s of sex and c o n t r a s t s e n s i t i v i t y . (p>.0l) The c o n t r a s t s e n s i t i v i t y f u n c t i o n s f o r the two groups are p l o t t e d i n F i g u r e 14 ( a s cending), F i g u r e 15 (descending), and 16 (combined). V a r i o u s c h a r a c t e r i s t i c s of the younger subsample (N=17) and o l d e r age group (N=17) are given in Table 4. As can be seen from the T - s t a t i s t i c s computed f o r the two groups, they only d i f f e r e d s i g n i f i c a n t l y on age and s p h e r i c a l c o r r e c t i o n . No s i g n i f i c a n t d i f f e r e n c e s were noted between groups on c y l i n d e r c o r r e c t i o n , a x i s of c y l i n d e r , best c o r r e c t e d S n e l l e n a c u i t y , diameter of d i l a t e d p u p i l , and i n t r a o c u l a r p r e s s u r e . A s i g n i f i c a n t o v e r a l l F<1,12) value f o r ascending t r i a l s f o r both a r i t h m e t i c (F=1.2) and geometric (F=1.18) mean c o n t r a s t s e n s i t i v i t y (p<.CM) was found by one-way a n a l y s i s of v a r i a n c e . Examination of each s p a t i a l frequency r e v e a l e d that s i g n i f i c a n t d i f f e r e n c e s - between the young and o l d age groups o c c u r r e d at 3, 70 > in z UJ tn 27 -i 24-21-18-15-1/1 12-< 2 O O 9-6-3-1 0-Legend A M A L E X F E M A L E 10 12 l 14 l 16 CYCLES/DEGREE F i g u r e 14: A r i t h m e t i c Mean C o n t r a s t S e n s i t i v i t y F u n c t i o n s ( A s c e n d i n g T r i a l s ) f o r Males and Females 71 27-, 2H Legend A MALE X FEMALE 6 8 10 CYCLES/DEGREE 12 14 16 F i g u r e 15: A r i t h m e t i c Mean C o n t r a s t S e n s i t i v i t y F u n c t i o n s (Descending T r i a l s ) f o r Males and Females \ 72 F i g u r e 16: A r i t h m e t i c Mean C o n t r a s t S e n s i t i v i t y F u n c t i o n s (Combined) f o r Males and Females T a b l e 4: T - t e s t s between Younger and Old e r Observers on V a r i o u s Measures Mean S t a n d a r d dev1 at i o n T - v a l u e df 2-tai1 p r o b a b i 1 1 t y Age young o l d 22 .6 6G . 2 2 . 7 7 . 2 -23.39 32 p<.000 Sphere young o l d -1 . 30 .647 2 . 3 1 .8 -2.76 32 p<.01 Cy11nder young o l d - .456 - .662 .95 . 88 .65 32 NS (not s1gn i f i cant ] A x i s ( i n de g r e e s ) young o l d 54 . 3 98 . 5 66.6 47 .O -2 . 24 32 NS Acu i t y young o l d 19 . 1 19.7 1 . 97 4.5 - . 49 32 NS Pup i 1 young o l d 7 .65 6 . 76 1 . 10 1 .00 2 . 39 32 NS I n t r a O c u l a r P r e s s u r e (mm/Hg) young o l d 13 . 76 16.11 2 .56 2.96 -2.48 32 NS F i g u r e 17: A r i t h m e t i c Mean C o n t r a s t S e n s i t i v i t y F u n c t i o n s ( A s c e n d i n g T r i a l s ) f o r Younger and O l d e r O b s e r v e r s F i g u r e 18: Geometric Mean C o n t r a s t S e n s i t i v i t y F u n c t i o n s ( A s c e n d i n g T r i a l s ) f o r Younger and O l d e r O b s e r v e r s 6 8 10 12 14 16 CYCLES/DEGREE Legend A YOUNG X OLD F i g u r e 19: A r i t h m e t i c Mean C o n t r a s t S e n s i t i v i t y F u n c t i o n s (Descending T r i a l s ) f o r Younger and O l d e r O b s e r v e r s 77 F i g u r e 20: Geometric Mean C o n t r a s t S e n s i t i v i t y F u n c t i o n s ( D e s c e n d i n g T r i a l s ) f o r Younger and O l d e r O b s e r v e r s 78 27-i 24-F i g u r e 21: A r i t h m e t i c Mean C o n t r a s t S e n s i t i v i t y F u n c t i o n s (Combined) f o r Younger and O l d e r O b servers F i g u r e 22: Geometric Mean C o n t r a s t S e n s i t i v i t y F u n c t i o n s (Combined) f o r Younger and O l d e r Observers o CO T a b l e 5: Group Means (arid S t a n d ard D e v i a t i o n s ) of I n d i v d i u a l C o n t r a s t T h r e s h o l d Standard D e v i a t i o n s 15 10 Cyc1es/Degree 7.5 6 1 .5 0. 75 ascend t ng young o l d d escend i ng young o l d 5.77(3.6) 6.03(3.5) 4 .97(3 . 7) 5.40(4.5) .60(2.9) 63(1.8) .74(2.4) .33(2.4) 19(1-1) .92(2.4) . 18(0.9) 43(3.6) 2.32(1.4 ) 3.13(2.1) 1.86(1.1) 2.33(1.0) 30(1.1) 30(1.8) .39(0.8) 78(1.2) .90(1.6) .85(2.9) 73(1.4) .61(5.2) 3.09(1.6 ) 5.56(2.9) s i g . p<.01 3.54( 1 .4) 5.62(3.3) T a b l e S: C o r r e l a t i o n C o e f f i c i e n t s between Age and A r i t h m e t i c C o n t r a s t S e n s i t i v i t y AGE a s c e n d i n g  d e s c e n d i n g o v e r a l 1 15 .079 . 24 1 .012 10 . 327 . 181 . 177 C y c l e s / D e g r e e 7.5 6 . 404 .015 . 284 .450 .093 . 307 . G24 . 148 . 44G 1 .5 . 56G . 175 .437 0. 75 . G89 .079 . 58 1 A l l c o r r e l a t i o n s o u t s i d e the range -.43 to +.43 are s i g n i f i c a n t p<.Q1 82 1.5, and .75 cyc/deg (p<.Ol). The descending and o v e r a l l means were not s i g n i f i c a n t at the .01 l e v e l . The c o n t r a s t s e n s i t i v i t y f u n c t i o n s f o r these two groups f o r d i f f e r e n t t h r e s h o l d d e f i n i t i o n s are shown in F i g u r e s 17-22. Standard d e v i a t i o n s of i n d i v i d u a l c o n t r a s t t h r e s h o l d s f o r ascending and descending t r i a l s are given in Table 5. These values i n d i c a t e that o l d e r i n d i v i d u a l s are more v a r i a b l e i n t h e i r i n d i v i d u a l t h r e s h o l d responses than younger i n d i v i d u a l s although only at .75 cyc/deg for ascending t r i a l s was t h i s d i f f e r e n c e s t a t i s t i c a l l y s i g n i f i c a n t (T(32)=-3.11, p<.0l). The r e l a t i v e l y l a r g e standard d e v i a t i o n s i n d i c a t e that there was a l a r g e d i f f e r e n c e i n observers in terms of the s t a b i l i t y of t h e i r t h r e s h o l d measures. Some i n d i v i d u a l s would be h i g h l y v a r i a b l e while others d i f f e r e d l i t t l e i n t h e i r t h r e s h o l d judgements at a p a r t i c u l a r s p a t i a l frequency. C o r r e l a t i o n c o e f f i c i e n t s were computed f o r s e v e r a l measures. Age was c o r r e l a t e d with c o n t r a s t s e n s i t i v i t y f o r a r i t h m e t r i c ascending, descending, and combined t h r e s h o l d s . I t appears t h a t , f o r ascending t r i a l s , with i n c r e a s i n g age comes poorer c o n t r a s t s e n s i t i v i t y . T h i s r e l a t i o n s h i p i s more pronounced as the s p a t i a l frequency diminishes (as the p a t t e r n becomes more c o a r s e ) . I t i s a l s o apparent from Table 6 that no s i g n i f i c a n t c o r r e l a t i o n e x i s t s f o r descending t r i a l s and age and only f o r the lowest s p a t i a l f r e q u e n c i e s f o r the o v e r a l l c o n t r a s t s e n s i t i v i t y v a l u e s . S p h e r i c a l and c y l i n d e r c o r r e c t i o n , best c o r r e c t e d S n e l l e n a c u i y , and i n t r a o c u l a r pressure were a l s o compared with a r i t h m e t i c c o n t r a s t s e n s i t i v i t y by c o r r e l a t i o n . These ro CO T a b l e 7: C o r r e l a t i o n C o e f f i c i e n t s f o r S p h e r i c a l , C y l i n d e r C o r r e c t i o n , Best C o r r e c t e d S n e l l e n A c u i t y , and I n t r a o c u l a r P r e s s u r e v e r s u s A r i t h m e t i c C o n t r a s t S e n s i t i v i t y (Ascending and O v e r a l l ) C y c l e s / D e g r e e 15 10 7.5 6 3 1.5 0.75 SPHERICAL CORRECTION a s c e n d i n g .122 -.043 -.079 -.186 -.298 -.201 -.239 o v e r a l 1 .111 .029 -.063 -.072 -.167 -.065 -.131 CYLINDER CORRECTION a s c e n d i ng -.082 -.032 .1 19 .232 .257 .247 .171 o v e r a l 1 -.094 -.072 .128 .171 .207 .172 .117 ACUITY a s c e n d i n g -.242 -.259 -.148 .008 -.047 -.105 -.125 o v e r a l 1 -.172 -.154 -.073 .063 -.049 -.140 -.242 INTRAOCULAR PRESSURE a s c e n d i n g -.101 -.001 -.180 -.234 -.143 -.013 -.233 o v e r a l 1 .065 -.045 -.240 -.263 -.142 -.055 -.205 No S t a t i s t i c a l l y S i g n i f i c a n t Values 84 c o r r e l a t i o n s are presented i n Table 7. The low c o r r e l a t i o n c o e f f i c i e n t s i n d i c a t e that there i s l i t t l e or no l i n e a r r e l a t i o n s h i p between any of these measures and c o n t r a s t s e n s i t i v i t y . L a s t l y , a r i t h m e t i c c o n t r a s t s e n s i t i v i t y at each s p a t i a l frequency was c o r r e l a t e d with every other s p a t i a l frequency that was d e r i v e d the same way. T h i s means that a l l ascending c o n t r a s t s e n s i t i v i t i e s were c o r r e l a t e d with each other and a l l descending e t c . These c o r r e l a t i o n s were obtained f o r the e n t i r e age sample (N=34) and s e p a r a t e l y f o r the young and o l d i n d i v i d u a l s . The c o r r e l a t i o n c o e f f i c i e n t s f o r these are given i n Table 8-10. I t i s apparent that s p a t i a l f r e q u e n c i e s c l o s e s t to each other ( c l o s e s t i n ter-ms of cyc/deg) are the most h i g h l y c o r r e l a t e d . T h i s c o r r e l a t i o n d i m i n i s h e s as the s p a t i a l f r e q u e n c i e s become more remote from each o t h e r . A l s o i t appears that s p a t i a l f r e q u e n c i e s f o r descending t r i a l s are more h i g h l y c o r r e l a t e d with each other than are ascending t r i a l s . CO T a b l e 8: I n t e r c o r r e l a t i o n s f o r C o n t r a s t S e n s i t i v i t y at a l l S p a t i a l F r e q u e n c i e s (Ascending T r i a l s ) Cyc/deg 15 10 7.5 6 3 1.5 .75 young o l d b o t h y o b y o b y o b y o b y o b y o b young 1.O .857 .762 .693 .636 .585 .266 15 o l d 1.0 .829 .536 .380 .460 .527 .472 b o t h 1.0 .821 .637 .546 , .497 .517 .330 young 1.0 .894 .833 .77 1 .726 .443 10 o l d 1.0 .839 .649 .487 .543 .570 b o t h 1.0 .885 .789 .688 .688 .574 young 1.0 .924 .847 .813 .540 7.5 o l d 1.0 .848 .690 .624 .639 b o t h 1.0 .906 .807 .770 .662 young 1.0 .712 .740 .521 6 o l d 1.0 814 .597 .600 b o t h 1.0 .795 .736 .643 young 1.0 .872 .636 3 o l d 1.0 .819 .698 b o t h 1.0 .889 .789 young 1.0 .695 1.5 o i d 1.0 .907 b o t h 1.0 .860 young 75 o l d both Young/01d: A l l v a l u e s o u t s i d e the range -.606 to +.606 are s i g n i f i c a n t p<.01 Both: A l l v a l u e s o u t s i d e the range -.43 to +.43 are s i g n i f i c a n t p<.01 1 .0 1 .0 1 .0 CO T a b l e 9: I n t e r c o r r e l a t i o n s f o r C o n t r a s t S e n s i t i v i t y at a l l S p a t i a l F r e q u e n c i e s ( O v e r a l l ) Cyc/deg 15 10 7.5 G 3 1.5 .75 young o l d b o t h y o b y o b y o b y o b y o b y o b young 1 .O .879 .782 .709 .687 .631 .490 15 o l d 1.0 .897 .758 .597 .560 .639 .596 b o t h 1.0 .877 .745 .631 .577 .582 .464 young 1.0 .909 .884 .853 .742 .640 10 o l d 1.0 .874 .752 .621 .588 .622 b o t h 1.0 .892 .819 .737 .674 .615 young 1.0 .934 .859 .803 .697 7.5 o l d 1.0 .894 .768 .655 .573 b o t h 1.0 , .917 .830 .761 .653 young 1.0 .753 .767 .667 6 O l d 1.0 .821 .528 .478 b o t h 1.0 .794 .712 .600 young 1.0 .802 .729 3 o l d 1.0 .775 .623 b o t h 1 0 .826 .734 young 1.0 .778 1.5 o l d 1.0 .84 1 b o t h 1.0 .824 young 75 o l d b o t h Young/01d: A l l v a l u e s o u t s i d e the range -.606 to +.606 are s i g n i f i c a n t p<.01 Both: A l l v a l u e s o u t s i d e the range -.43 to +.43 are s i g n i f i c a n t p<.01 1 .0 1 .0 1 .0 0 0 T a b l e 10: I n t e r c o r r e l a t i o n s f o r C o n t r a s t S e n s i t i v i t y at a l l S p a t i a l F r e q u e n c i e s (Descending T r i a l s ) Cyc/deg 15 10 7.5 6 3 1.5 .75 young o l d b o t h y o b y o b y o b y o b y o b y o b young 1.0 .897 .780 .686 .669 .628 .653 15 o l d 1.0 .918 .957 .955 .705 .632 .453 both 1.0 .908 .864 .874 .684 .403 .435 young 1.0 .914 .886 .861 .782 .773 10 o l d 1.0 .845 .832 .851 .658 .604 both 1.0 .838 .835 .850 .536 .608 young 1.0 .880 .758 .764 .740 7.5 O l d 1.O .985 .675 .617 .342 b o t h 1.0 .950 .690 .619 .435 young 1.0 .74 1 .830 .773 6 o l d 1.0 .625 .530 .300 both 1.0 .656 .580 .396 young 1.0 .7 26 .800 S o l d 1.0 .739 .620 both 1.0 .599 .638 young 1.0 .753 1.5 o l d 1.0 .821 b o t h , 1 . 0 . 6 6 5 young 75 o l d both Young/01d: A l l v a l u e s o u t s i d e the range -.606 to +.606 are s i g n i f i c a n t p<.01 Both: A l l v a l u e s o u t s i d e the range -.43 to +.43 a r e s i g n i f i c a n t p<,01 1 .0 1 .0 1 .0 88 D i s c u s s i o n I t appears that gender of observer i s not a s i g n i f i c a n t f a c t o r i n s p a t i a l c o n t r a s t s e n s i t i v i t y . In t h i s i n s t a n c e , one-way a n a l y s i s of v a r i a n c e r e v e a l e d no s i g n i f i c a n t d i f f e r e n c e s i n mean c o n t r a s t scores at any of the s p a t i a l f r e q u e n c i e s t e s t e d for e i t h e r ascending, descending, or combined t h r e s h o l d measurements. Given t h i s s i m i l a r i t y i n s p a t i a l c o n t r a s t s e n s i t i v i t y between i n d i v i d u a l s of d i f f e r i n g gender, i t appeared p e r m i s s i b l e to examine age and the CSF without regard to gender of the observer. As such, a n a l y s i s was performed on the e n t i r e age sample i r r e s p e c t i v e of gender. Even so, as an added p r e c a u t i o n , both age groups c o n s i s t e d of the same number of i n d i v i d u a l s of i d e n t i c a l gender (5 male and 12 female). Before c o n s i d e r i n g the e f f e c t of ageing upon the CSF i t would be b e n e f i c i a l to know what i s or what i s not i n f l u e n c i n g the c o n t r a s t s e n s i t i v i t y f u n c t i o n d e r i v e d f o r each observer. Examination of the c o r r e l a t i o n between r e f r a c t i v e c o r r e c t i o n ( s p h e r i c a l and c y l i n d e r values) and c o n t r a s t s e n s i t i v i t y at each s p a t i a l frequency i n d i c a t e s that there i s l i t t l e r e l a t i o n s h i p between these measures. Apparently f o r t h i s range of s p h e r i c a l and c y l i n d e r c o r r e c t i o n s at l e a s t , the i n t e r f e r o m e t e r used to determine s p a t i a l c o n t r a s t s e n s i t i v i t y i s u n a f f e c t e d by an observer's f o c u s i n g apparatus. Low c o r r e l a t i o n s between best c o r r e c t e d S n e l l e n a c u i t y and c o n t r a s t s e n s i t i v i t y as we l l as i n t r a o c u l a r pressure and c o n t r a s t s e n s i t i v i t y a l s o i n d i c a t e that for these s u b j e c t s l i t t l e r e l a t i o n s h i p e x i s t s on these measures. T h i s does not mean however that there i s no i n f l u e n c e of 89 i n t r a o c u l a r p r e s s u r e or maximum r e a l i z a b l e S n e l l e n a c u i t y on c o n t r a s t s e n s i t i v i t y . That i s , the p o s s i b i l i t y that an IOP ou t s i d e of the range sampled i n t h i s study (highest IOP 21 mm. hg.) or a best c o r r e c t e d S n e l l e n a c u i t y c o n s i d e r a b l y poorer than the worst i n t h i s sample of i n d i v i d u a l s (the poorest i n t h i s sample was onl y 20/30) may exert some i n f l u e n c e on the CSF. Of course such c o n j e c t u r e c o u l d be s e t t l e d e x p e r i m e n t a l l y . While there appears to be l i t t l e i n f l u e n c e of these p r e r e c e p t o r a l f a c t o r s on the CSF i n t h i s i n s t a n c e , other p r e r e c e p t o r a l v a r i a b l e s of which no measures were recorded, are sure to a f f e c t the CSF. For example, i t i s evident that l e n t i c u l a r o p a c i t y a f f e c t s the CSF. Whether the mechanism of i t s e f f e c t on the CSF i s analogous to lowering the mean p a t t e r n luminance or cau s i n g i n c r e a s e d s c a t t e r i n g of 1 i g h t — e s s e n t i a l l y d e focusing--as i t i s d i f f r a c t e d by the o p a c i t i e s i n the l e n s , the e f f e c t upon the CSF would be very s i m i l a r . Both changes r e s u l t i n a maximal decrease i n c o n t r a s t s e n s i t i v i t y f o r higher s p a t i a l f r e q u e n c i e s with l i t t l e change at lower s p a t i a l f r e q u e n c i e s . T h i s knowledge l e d to e x c l u s i o n of those i n d i v i d u a l s found to have s i g n i f i c a n t l e n t i c u l a r o p a c i t y by s l i t - l a m p examination and so no r e c o r d of lens c l a r i t y was u t i l i z e d i n the present study. The age groups were s i m i l a r i n terms of c o r n e a l and lens c l a r i t y as w e l l as having c l e a r o p t i c media. In f a c t T - t e s t s of p o s s i b l e group d i f f e r e n c e s on s e v e r a l v a r i a b l e s i n d i c a t e d that the two groups d i f f e r e d s i g n i f i c a n t l y i n terms of age and s p h e r i c a l c o r r e c t i o n . The q u e s t i o n a r i s e s as to whether t h i s p a r t i c u l a r o l d e r sample i s r e p r e s e n t a t i v e of ol d e r i n d i v i d u a l s i n g e n e r a l . Probably not. If anything t h i s 90 p a r t i c u l a r sample c o n s t i t u t e s a group of aged i n d i v i d u a l s who are s u p e r i o r to t h e i r e q u i v a l e n t p o p u l a t i o n i n which one o f t e n encounters higher r e f r a c t i v e e r r o r as we l l as a decrease i n l e n t i c u l a r c l a r i t y . Given the p o s s i b i l i t y that t h i s aged sample i s e i t h e r r e p r e s e n t a t i v e of or superior to i t s e q u i v a l e n t p o p u l a t i o n , the f i n d i n g that t h i s group's c o n t r a s t s e n s i t i v i t y i s s i g n i f i c a n t l y poorer at low s p a t i a l frequencies (3, 1.5, and .75 cyc/deg) than a younger aged group i s q u i t e remarkable. I n t e r e s t i n g l y t h i s group d i f f e r e n c e d i d not appear f o r descending t h r e s h o l d measurements. Examination of F i g u r e s 17 through 22 r e v e a l s the c o n s i d e r a b l e d i f f e r e n c e between ascending and descending t h r e s h o l d s . Younger observers had s u p e r i o r c o n t r a s t s e n s i t i v i t y at a l l s p a t i a l f r e q u e n c i e s than o l d e r observers f o r means c a l c u l a t e d e i t h e r a r i t h m e t i c a l l y or g e o m e t r i c a l l y . On descending t r i a l s , however, f o r some s p a t i a l f r e q u e n c i e s the o l d e r group proved s u p e r i o r t o the younger although not s i g n i f i c a n t l y s t a t i s t i c a l l y , (see Fig u r e 19 and 20) Most l i k e l y t h i s l a c k of group d i f f e r e n c e f o r descending stimulus measurement caused the n o n s i g n i f i c a n t combined t h r e s h o l d i n t h i s i n s t a n c e . The hig h v a r i a b i l i t y of t h r e s h o l d using the Bekesy t r a c k i n g p r o c e d u r e — which i s q u i t e c l o s e to ascending and descending t r i a l s — w a s a l s o noted by Ginsburg and Cannon (1983) who r e p o r t e d the highest average standard d e v i a t i o n f o r t h i s measurement method and the lowest f o r the method of i n c r e a s i n g c o n t r a s t (ascending method). They a l s o report that c o n t r a s t s e n s i t i v i t y f o r the Bekesy method i s the hi g h e s t . In view of the c o n t r a s t s e n s i t i v i t y found here f o r descending t r i a l s , i t i s q u i t e 91 evident what i s r e s p o n s i b l e f o r the i n c r e a s e d c o n t r a s t s e n s i t i v i t y found fo r the Bekesy method versus the ascending s t i m u l i method. A r e a l d i f f e r e n c e e x i s t s between t h r e s h o l d s determined by these two methods. Why should t h i s be so? One p o s s i b l e e x p l a n a t i o n c o u l d be p o s t u l a t e d at the l e v e l of the photoreceptors themselves where f o r descending t r i a l s the r e c e p t o r s go from a h i g h l y a c t i v a t e d s t a t e (bleached photopigments) to one of l e s s e n e d p h o t i c s t i m u l a t i o n versus ascending t r i a l s where the i n i t i a l amount of pigment b l e a c h i n g i s minimal. The d i f f e r e n c e between ascending and descending t r i a l s a l s o can be noted i n Tables 8 and 10 where c o r r e l a t i o n s between s p a t i a l f r e q u e n c i e s i n d i c a t e s that s p a t i a l f r e q u e n c i e s t e s t e d by descending method g e n e r a l l y more h i g h l y i n t e r c o r r e l a t e than when t e s t e d by the ascending method. The i n t e r c o r r e l a t i o n s between v a r i o u s s p a t i a l f r e q u e n c i e s f o r a l l the measurement methods i n d i c a t e s that i n general i f a s u b j e c t had good c o n t r a s t s e n s i t i v i t y at one s p a t i a l frequency, they tended to do w e l l at a l l the others although t h i s tendency decreased as s p a t i a l f r e q u e n c i e s became more remote. So, f o r example, a h i g h c o n t r a s t s e n s i t i v i t y at 15 cyc/deg i s very l i k e l y to be a s s o c i a t e d with s i m i l a r performance at 10 cyc/deg but l e s s l i k e l y f o r .75 cyc/deg. These g e n e r a l i t i e s seemed to apply f o r both age groups. Whether these h i g h c o r r e l a t i o n s f o r adjacent s t i m u l i i n d i c a t e that some s p a t i a l f r e q u e n c i e s being examined are redundant and c o u l d be omitted without l o s s of important i n f o r m a t i o n i s not known. If t h i s range of s p a t i a l f r e q u e n c i e s was u t i l i z e d to examine o c u l a r pathology as opposed to nonpathologic eyes, i t i s p o s s i b l e that omission of 2 or 3 s p a t i a l f r e q u e n c i e s may cause some s e l e c t i v e impairment to go undetected. Given the noted l o s s at low s p a t i a l f r e q u e n c i e s found here, one wonders what d i f f e r e n c e s e x i s t between t h i s study and those who report l o s s only at h i g h s p a t i a l f r e q u e n c i e s . U n f o r t u n a t e l y s e v e r a l stimulus v a r i a b l e s d i f f e r between t h i s study and those p r e v i o u s l y r e p o r t e d in the l i t e r a t u r e making i t very d i f f i c u l t to p i n p o i n t e x a c t l y what i s c o n t r i b u t i n g to t h i s d i f f e r e n c e . Comparison of Sekuler and Hutman's methodology i n t h e i r 1980 paper with t h e i r more recent work i n d i c a t e s v a r i o u s d i f f e r e n c e s in stimulus parameters: 1) temporal modulation, 2) mean t a r g e t luminance, and 3) luminance of surround (see Table 3) and 4) r a t e of c o n t r a s t change. On t h i s l a s t v a r i a b l e , t h e i r e a r l i e r work appears to report r e s u l t s based upon a higher r a t e of c o n t r a s t change than t h e i r l a t e r work. The former c o n t r a s t being v a r i e d at 4 db/sec and the l a t t e r at a v a r i a b l e r a t e (as i t was not l i n e a r at d i f f e r e n t c o n t r a s t l e v e l s ) in the region of .1 l o g u n i t / s e c to .035 l o g u n i t / s e c . While i t i s not s p e c i f i e d what they meant by a db i t i s l i k e l y that t h i s value i s g r e a t e r than 1 l o g u n i t / s e c and r e p r e s e n t s a f a s t e r r a t e of c o n t r a s t change. Rate of c o n t r a s t change has been shown to i n f l u e n c e c o n t r a s t s e n s i t i v i t y by Ginsburg and Cannon (1983) who v a r i e d percent c o n t r a s t per second of a 4 cyc/deg g r a t i n g p a t t e r n and found that past a c e r t a i n rate c o n t r a s t s e n s i t i v i t y d e c l i n e d . One should a l s o note the d i f f e r e n c e between d i s c r e t e l y presented versus dyna m i c a l l y a l t e r e d s t i m u l i (see Appendix Two). The low s p a t i a l f r e q u e n c i e s do appear to be a f f e c t e d by many temporal f a c t o r s that seem to cause l i t t l e change in high s p a t i a l 93 f r e q u e n c i e s . R e c a l l , f o r example the in c r e a s e d c o n t r a s t s e n s i t i v i t y at low s p a t i a l f r e q u e n c i e s to temporal phase r e v e r s a l and the e f f e c t of the shape of the temporal envelope (see p. 33) on c o n t r a s t s e n s i t i v i t y . F l i c k e r d e t e c t i o n and dynamic stimulus d e t e c t i o n i s often r e p o r t e d to be impaired in ol d e r i n d i v i d u a l s so t h i s d i f f e r e n c e between t h e i r two r e p o r t s may prove s i g n i f i c a n t . In the present study rate of c o n t r a s t change, while not recorded, would c e r t a i n l y be c l o s e r to the f a s t e r r a t e of c o n t r a s t change than the slower. It should be evident from the p r i o r d i s c u s s i o n of mean p a t t e r n luminance as w e l l as luminance of background (see p.43-47) that these two v a r i a b l e s , probably along with f i e l d s i z e , can i n f l u e n c e the CSF. One i n t e r e s t i n g p o s t u l a t i o n a r i s e s from K e l l y (1970) (see p.37) who noted that an abrupt r e t i n a l edge brought about by having mean t a r g e t luminance g r e a t e r than that of the surround and the boarder of the stimulus as a luminance peak as opposed to a trough of the s i n e wave may l e a d to inc r e a s e d s e n s i t i v i t y f o r that s p a t i a l frequency as t h i s abrupt edge i s e a s i e r to detect than the p a t t e r n ' s s p a t i a l frequency. T h i s abrupt edge would be analogous to a very high s p a t i a l frequency and c e r t a i n l y o c c u r r e d i n the present study where the c i r c u l a r p a t t e r n ' s edges along a h o r i z o n t a l d i r e c t o n were composed of luminance peaks (at minimum 3.5 cd/m 2) and these were viewed on a dark (.1 cd/m 2) surround. I f the younger observers were able to r e s o l v e f r e q u e n c i e s w e l l above the 15 cyc/deg t e s t e d and the o l d e r observers have a lower c u t o f f s p a t i a l frequency, than t h i s abrupt edge would be l e s s h e l p f u l to the o l d e r group. 94 The p o s s i b i l i t y that choice of stimulus v a r i a b l e s may i n f l u e n c e e i t h e r the magnitude of an age d i f f e r e n c e i n s e n s i t i v i t y or where the d i f f e r e n c e occurs leads one to wonder whether i t would be p o s s i b l e to s e l e c t parameters that would optimize t h i s d i f f e r e n c e j u s t as i t may be p o s s i b l e to do so in the examination of o c u l a r pathology by s p a t i a l c o n t r a s t s e n s i t i v i t y . I t i s somewhat g r a t i f y i n g to note that numeric method of c a l c u l a t i n g t h r e s h o l d ( a r i t h m e t i c versus geometric mean) does not g r e a t l y change the CSF f o r ascending and combined. Descending t r i a l s were most e f f e c t e d . T h i s i s evident from comparisons of F i g u r e s 17 with 18, 19 with 20 and 21 with 22. C e r t a i n l y s u b j e c t s e l e c t i o n w i l l i n f l u e n c e the CSF, i t i s p r e c i s e l y f o r t h i s reason that s u b j e c t s with such confounds as l e n s o p a c i t y and o c u l a r pathology were excluded from the study. One v i r t u e of the i n t e r f e r o m e t e r used to examine the CSF i s i t s r e l a t i v e independence- of r e f r a c t i v e s t a t e of the eye. If Campbell and Green's (1965; see p.27) r e p o r t of the p e r v a s i v e e f f e c t on the eye of a s l i g h t l y l e s s than optimum r e f r a c t i v e c o r r e c t i o n f o r d e t e c t i o n of h i g h s p a t i a l f r e q u e n c i e s i s a c c u r a t e , then any other "age" s t u d i e s using o s c i l l o s c o p e type d i s p l a y s must be very c a r e f u l to r e f r a c t each s u b j e c t o p t i m a l l y f o r t h at t e s t d i s t a n c e . Any e r r o r i n r e f r a c t i v e c o r r e c t i o n (at l e a s t s p h e r i c a l ) w i l l r e s u l t i n a s p u r i o u s l o s s i n c o n t r a s t s e n s i t i v i t y to h i g h s p a t i a l f r e q u e n c i e s while h a r d l y i n f l u e n c i n g c o n t r a s t s e n s i t i v i t y f o r low s p a t i a l f r e q u e n c i e s . Other measures i n d i c a t e d i f f e r e n c e s between the two age groups. C o r r e l a t i o n of age and c o n t r a s t s e n s i t i v i t y at each 95 s p a t i a l frequency i n d i c a t e s that lower c o n t r a s t s e n s i t i v i t y i s a s s o c i a t e d with i n c r e a s i n g age of the observer. T h i s r e l a t i o n s h i p i s g r e a t e s t f o r the lowest s p a t i a l frequency and decreases with i n c r e a s i n g s p a t i a l frequency (see Table 6). I t i s a l s o evident from Table 5 that the o l d e r i n d i v i d u a l s f l u c t u a t e d more in t h e i r t h r e s h o l d v a l u e s - - t h a t i s i n d i v i d u a l v a r i a b i l i t y i n t h r e s h o l d — t h a n d i d the younger observers and that the range of t h i s i n d i v i d u a l v a r i a b i l i t y was mostly g r e a t e r i n the o l d e r group. That o l d e r observers are more v a r i a b l e has been mentioned p r e v i o u s l y (eg. P i t t s , 1982) and i s confirmed by the present study. Given t h a t , i n t h i s i n s t a n c e at l e a s t , the CSF i s l a r g e l y u n e f f e c t e d by the p r e r e c e p t o r a l components of the eye, one would l i k e to know what neural changes have occurred that c o u l d cause t h i s l o s s at low s p a t i a l f r e q u e n c i e s and yet leave high s p a t i a l f r e q u e n c i e s u n a f f e c t e d . Perhaps i t would be best to c o n s i d e r j u s t what i s being examined by t h i s p a r t i c u l a r t e s t . I t i s evident from microspectrophotometric measurements made by D a r t n a l l e t . a l . (1983) that a red He-Ne l a s e r ( Xd=632.8 nm.) c o u l d be s t i m u l a t i n g "red" and p o s s i b l y "green" cones. In f a c t they suggest that there may e x i s t two subpopulations of red cones one with a Xmax of 563.2±3.1 nm. (27 of 58 red cones sampled) and a short wavelength red cone with Xmax of 554.2±2.3 nm. (31 of 58 sampled). Perhaps then the maximal e f f e c t of t h i s extreme red l i g h t would be on these long wavelength cones? One would then have to e x p l a i n the d i f f e r e n c e i n s p a t i a l frequency s e n s i t i v i t y as being r e l a t e d to the s p a t i a l l o c a t i o n on the r e t i n a of these cones and t h e i r s e l e c t i v e l o s s with aging. 96 Another p o s s i b i l i t y , at the photoreceptor l e v e l was suggested by Dr. Lakowski who p o s t u l a t e d some type of a l t e r a t i o n i n the d i r e c t i o n a l s e n s i t i v i t y of cones with aging. The broad p a t t e r n s being l e s s e f f e c t i v e l y sensed than the narrow bands. Some type of a l t e r a t i o n i n d i r e c t i o n a l s e n s i t i v i t y with aging i s supported by the report of M a r s h a l l (1979) who found t h a t human cones showed dramatic morphological changes with age. "In the young a d u l t , cones are seen to have w e l l - o r d e r e d d i s c membranes the e n t i r e l e n g t h of t h e i r outer segments. With i n c r e a s i n g age the order i n the cone outer segment membrane decreases....By the 8th and 9th decades of l i f e , human cone outer segment membranes are h i g h l y d i s o r g a n i z e d . " (p.377.) and appear by e l e c t r o n microscopy as s h r i v e l e d and somewhat n e c r o t i c . It appears though that more than j u s t cones change with age. Comparison of r e t i n a l ganglion c e l l axon p o p u l a t i o n s i n young and o l d e r i n d i v i d u a l s i n d i c a t e s that o l d e r i n d i v i d u a l s may have fewer axons than do younger i n d i v i d u a l s . Quigley e t . a l . (1982) give a 95% confidence i n t e r v a l f o r 5 normal s u b j e c t s (age range 58-86 years) as 827,498-1,100,366 axons. A p r e v i o u s study by P o t t s e t . a l . (1972) r e p o r t e d counts of 1,163,100 and 1,273,802 m i l l i o n f i b e r s f o r two i n d i v i d u a l s aged 35 and 25 years r e s p e c t i v e l y . Both of these v a l u e s are o u t s i d e of the 95% confidence i n t e r v a l f o r the o l d e r age group. I f low s p a t i a l frequency maximally s e l e c t s only a c e r t a i n type of g a n g l i o n c e l l axon, analogous to f o r example, the "Y" type found i n the c a t perhaps t h i s type of c e l l i s the f i r s t to d e c l i n e with age i n the c e n t r a l region of the r e t i n a or i f they a l l d e c l i n e , perhaps the f i r s t to be n o t i c e d as m i s s i n g . T h i s would i n d i c a t e more 97 redundancy of the highest a c u i t y - - f i n e d e t a i l d e t e c t o r s i n the c e n t r a l region of the r e t i n a and l e s s of the l a r g e s p a t i a l frequency, time dependant d e t e c t o r s . However t h i s does not exhaust a l l the p o s s i b i l i t i e s as Devaney and Johnson (1980) i n d i c a t e that the macular p r o j e c t i o n region of the human v i s u a l c ortex (the r o s t r a l s u r f a c e of the r o s t r a l t h i r d of the i n f e r i o r c a l c a r i n e gyrus) c o n t a i n s l e s s neurons per gram of t i s s u e i n the o l d e r than younger i n d i v i d u a l s . Measurement of 23 i n d i v i d u a l s between 20 and 87 years by the c e l l d i s p e r s i o n technique i n d i c a t e d that a 54% l o s s in neuron p o p u l a t i o n d e n s i t y occurred from the youngest to o l d e s t ages examined. Whether some, one, or a l l of these changes are c o n t r i b u t i n g to the noted change i n s p a t i a l c o n t r a s t s e n s i t i v i t y with i n c r e a s i n g age cannot be r e s o l v e d by the present study and awaits f u r t h e r experimentation. 98 References A l p e r n , M. (1984) On the P r e s e n t a t i o n of the Friedenwald Award i n Ophthalmology to C h r i s t i n a E n r o t h - C u g e l l and John G. Robson. Inv. Ophthal. and V i s . S c i . , 25(3) , 245-249. Anderson,C. and S j o s t r a n d , J . (1981) Contrast S e n s i t i v i t y and C e n t r a l V i s i o n i n Reattached Macula. Acta  Ophthalmoloqica 59 ,161-169. A r n u l f , A. and Dupuy, 0. (1960) La t r a n s m i s s i o n des c o n t r a s t e s par l e systeme optique de l ' o e i l et l e s s e u i l s des c o n t r a s t e s r e t i n i e n s . C. r . hebd. Seanc.  Acad. S c i . , P a r i s . 250, 2757-2759. Arundale,K. (1978) An i n v e s t i g a t i o n i n t o the v a r i a t i o n of human c o n t r a s t s e n s i t i v i t y with age and o c u l a r pathology. Br. J . Ophthalmol., 62 ,213-215. Bodis-Wollner,I and Diamond,S. (1976) The Measurement of S p a t i a l Contrast S e n s i t i v i t y i n Cases of B l u r r e d V i s i o n A s s o c i a t e d with C e r e b r a l L e s i o n s . B r a i n , 99, 695-710. Brabyn,L.B. and McGuinness,D. (1979) Gender d i f f e r e n c e s i n response to s p a t i a l f r e q u e n c i e s and stimulus o r i e n t a t i o n . Percept• Psychophys., 26, 319-324. Byram, G. (1944) The P h y s i c a l and Photochemical B a s i s of V i s u a l R e solving Power. Part I I . V i s u a l A c u i t y and the Photochemistry of the R e t i n a . J . Opt. Soc. Am. 34(12), 718-738. Campbell,F. W. and Green,D. G. (1965) O p t i c a l and r e t i n a l f a c t o r s a f f e c t i n g v i s u a l r e s o l u t i o n . J ^ P h y s i o l . , 181, 576-593. Campbell,F. W. and Gubisch,R. (1966) O p t i c a l q u a l i t y of the human eye. J . P h y s i o l . 186, 558-578. Campbell,F. W., and Robson,J. (1968) A p p l i c a t i o n of F o u r i e r A n a l y s i s to the V i s i b i l i t y of G r a t i n g s . J . P h y s i o l .  197, 551-566. C l i n e , D . , H o f s t e t t e r , H , and G r i f f i n , J . (1980) D i c t i o n a r y of  V i s u a l Science (3rd.) Radnor Pa.: C h i l t o n Book Co. Coren, S., P o r a c , C , and Ward,L. ( 1984) Sensation and  Pe r c e p t i o n 2nd ed. Orlando F l a . : Academic P r e s s . Cornsweet, T. (1970) V i s u a l P e r c e p t i o n New York: Academic Pr e s s . D a r t n a l l , H., Bowmaker,J. and M o l l o n , J . (1983) Human v i s u a l 99 pigments: microspectrophotometric r e s u l t s from the eyes of seven persons. Proc. R. Soc. Lond. B.220 115-1 30. D e r e f e l d t , G . , Lennerstrand,G. and Lundh,B. (1979) Age v a r i a t i o n s i n normal human c o n t r a s t s e n s i t i v i t y . Acta  Ophthalmologica, 57, 679-690. Devaney, K. and Johnson, H. (1980) Neuron Loss i n the Aging V i s u a l Cortex of man. J . G e r o n t o l . 35(6), 836-841. Ditchburn, R.W. (1973) V i s u a l P e r c e p t i o n Oxford: Clarendon P r e s s . Dressier,M. and Rassow,B. (1981) Neural c o n t r a s t s e n s i t i v i t y measurements with a l a s e r i n t e r f e r e n c e system f o r c l i n i c a l and s c r e e n i n g a p p l i c a t i o n . Invest.  Ophthalmol, and V i s . S c i . 21(5), 737-744. Enr o t h - C u g e l l , C . and Robson,J.G. (1966) The c o n t r a s t s e n s i t i v i t y of r e t i n a l g a n g l i o n c e l l s of the c a t . J ^ P h y s i o l . 187, 517-552. En r o t h - C u g e l l , C . and Robson,J.G. (1984) F u n c t i o n a l C h a r a c t e r i s t i c s and D i v e r s i t y of Cat R e t i n a l Ganglion C e l l s . Inv. Ophthal. and V i s . S c i . 25(3) 250-267. Essock,E. (1982) A n i s o t r o p i e s of p e r c e i v e d c o n t r a s t and d e t e c t i o n speed. V i s . Res., 22, 1185-1191. F u l l e r , D and Hutton, W. (1982) P r e s u r g i c a l E v a l u a t i o n of  Eyes with Opaque Media New York: Grune and Stratton,p.22-28. Francon,M. (1979) Laser Speckle and A p p l i c a t i o n s in O p t i c s . New York: Academic Press. Ginsburg,A. and Cannon,M. (1983) Comparison of Three Methods f o r Rapid Determination of T h r e s h o l d C o n t r a s t S e n s i t i v i t y . Inv. Ophthal. and V i s . S c i . 24, 798-802. Granger, E. and H e u r t l e y , J . (1973) V i s u a l c h r o m a t i c i t y -modulation t r a n s f e r f u n c t i o n . J . Opt. Soc. Am. 63(9), 1173-1174. H a l l i d a y , B and Ross, J . (1983) Comparison of 2 i n t e r f e r o m e t e r s f o r p r e d i c t i n g v i s u a l a c u i t y i n p a t i e n t s with c a t a r a c t . Br. J . Ophthalmol. 67, 273-277. H a r t l i n e , H.K. and R a t l i f f , F . (1957) I n h i b i t o r y i n t e r a c t i o n of r e c e p t o r u n i t s i n the eye of Limulus. J . Gen.  P h y s i o l . 40, 357-376. Hess,R. and Howell,E. (1977) The Threshold C o n t r a s t S e n s i t i v i t y F u n c t i o n i n S t r a b i s m i c Amblyopia: Evidence 100 fo r a two type c l a s s i f i c a t i o n . V i s . Res. 17 1049-1055. Higgins,K., Caruso,R., C o l e t t a , N . , and de Monasterio,F. (1983) E f f e c t of A r t i f i c i a l C e n t r a l Scotoma on the S p a t i a l Contrast S e n s i t i v i t y of Normal S u b j e c t s . Inv.  Ophthalmol, and V i s . S c i . 24, 1131-1138. Higgins,K., Jaffe,M., C o l e t t a , N . , Caruso,R., and de Monasterio,F. (1984) S p a t i a l Contrast S e n s i t i v i t y . Importance of C o n t r o l l i n g the P a t i e n t ' s V i s i b i l i t y C r i t e r i o n . Arch. Ophthal. 102(7), 1035-1041. Hoekstra,J., van der Goot,D., van der Brink,G. and B i l s e n , F . (1974) The Infl u e n c e of the Number of Cy c l e s Upon the V i s u a l C o n t r a s t Threshold f o r S p a t i a l Sine Wave Pa t t e r n s V i s . Res. 14, 365-368. Howell,E. R. and Hess,R. F. (1978) The f u n c t i o n a l area f o r summation to t h r e s h o l d f o r s i n u s o i d a l g r a t i n g s . V i s . Res. 18, 369-374. Hutman,L. and Sekuler,R. (1980) S p a t i a l v i s i o n and aging I I : c r i t e r i o n e f f e c t s . Gerontology, 35(5), 700-706. Hyvarinen,L., Laurinen,P., and Rovamo,J. (1983) Contrast S e n s i t i v i t y i n E v a l u a t i o n of V i s u a l Impairment Due to Macular Degeneration'and O p t i c Nerve L e s i o n s . Acta  Ophthalmoloqica 61, 161-170. Jamar,J. and Koenderink,J. (1984) Dependence of Contrast D e t e c t i o n and Independence of AM and FM D e t e c t i o n on R e t i n a l Illuminance V i s . Res. 24(6), 625-629. Kelly,D.H. (1970) E f f e c t s of Sharp Edges on the V i s i b i l i t y of S i n u s o i d a l G r a t i n g s . J . Opt. Soc. Am. 60(1) 98-103. Kelly,D.H. (1973) I n h i b i t i o n i n Human Colour Mechanisms. J .  P h y s i o l . 228, 55-72. Kelly,D.H. (1981) Disappearance of S t a b i l i z e d Chromatic G r a t i n g s Science 214(11), 1257-1258. Lennie,P. (1980) P a r a l l e l V i s u a l Pathways: A Review V i s . Res. 20(7), 561-594. Loshin,D. and White,J. (1984) Contrast S e n s i t i v i t y : The V i s u a l R e h a b i l i t a t i o n o f . t h e P a t i e n t With Macular Degeneration. Arch. Ophthalmol. 102(9), 1 303-1306. Luckiesh,M and Moss,F. (1937) The Science of Seeing. New York: D. Van Nostrand Co. Inc. Lundh,B., D e r e f e l d t , G . , Nyberg,S., and Lennerstrand,G. (1981) P i c t u r e S i m u l a t i o n of Contrast S e n s i t i v i t y i n Organic and F u n c t i o n a l Amblyopia. Acta Ophthalmoloqica  59, 774-783. 101 Lundh,B., Lennerstrand,G. and D e r e f e l d t , G . (1983) C e n t r a l and P e r i p h e r a l Normal Contrast S e n s i t i v i t y f o r S t a t i c and Dynamic S i n u s o i d a l G r a t i n g s . Acta Ophthalmologica  61, 171-182,1983. M a r s h a l l , J . (1979) Ageing changes in human cones. In Shimizu,K. (ed.) Proceedings of the XXIII  I n t e r n a t i o n a l Congress of Ophthalmology, Kyoto, May  1978. Amsterdam: Excerpta Medica. McCann,J. and H a l l , J . J r . (1980) E f f e c t s of average-luminance surrounds on the v i s i b i l i t y of sine-wave g r a t i n g s . J . Opt. Soc. Am. 70(2) , 212-219. McGrath,C. and M o r r i s o n , J . (1981) A g e - r e l a t e d changes i n s p a t i a l frequency p e r c e p t i o n . J . P h y s i o l . 310, 52P. M i t c h e l l , D , Freeman,R. and Westheimer,G. (1967) E f f e c t of O r i e n t a t i o n on the Modulation S e n s i t i v i t y for I n t e r f e r e n c e F r i n g e s on the R e t i n a . J . Opt. Soc. Am.  57(2) , 246-249. de Monasterio,F.M. (1978a) P r o p e r t i e s of C o n c e n t r i c a l l y Organized X and Y Ganglion C e l l s of Macaque R e t i n a . J .  Neur o p h y s i o l . 41(6), 1394-1417. de Monasterio,F.M. (1978b) Center and Surround Mechanisms of Opponent-Color X and Y Ganglion C e l l s of Retina of Macaques. J . Neu r o p h y s i o l . 41(6), 1418-1434. de Monasterio,F.M. (1978c) P r o p e r t i e s of Ganglion C e l l s With A t y p i c a l R e c e p t i v e - F i e l d O r g a n i z a t i o n i n Retina of Macaques. J . Ne u r o p h y s i o l . 41(6), 1435-1449. Neb l e t t e , C . and Murray,A. (1973) Photographic Lenses New York: Morgan and Morgan, Inc. Owsley,C, Sekuler,R. and Siemsen,D. (1983) Contrast s e n s i t i v i t y throughout adulthood. V i s . Res., 23(7), 689-699. P h e l p s , C D . and Motolko,M. (1983) Contrast S e n s i t i v i t y and Glaucoma In K r i e g l s t e i n , G . and Leydhecker,W. (eds.) Glaucoma Update II Springer-Verlag,p.103-105. P i t t s , D . (1982) The e f f e c t s of Aging on S e l e c t e d V i s u a l F u n c t i o n s : Dark Adaptation, V i s u a l A c u i t y , S t e r e o p s i s , and B r i g h t n e s s C o n t r a s t . In Sekuler,R., Kline,D., and Dismukes,K. Eds. Aging and Human V i s u a l F u n c t i o n . New York: Alan R L i s s Inc.,p.131-159. Potts,A.,Hodges,D. and Shelman,C., F r i t z , K . , Levy,N. and Mangnall,Y. (1972) Morphology of the primate o p t i c nerve. I . Method and t o t a l f i b e r count. Inv. Ophthal. and V i s . S c i . 11(12) 980-988. 1 02 Quigley,H., Addicks,E. and Green,R. (1982) Op t i c Nerve Damage i n Human Glaucoma I I I . Q u a n t i t a t i v e C o r r e l a t i o n of Nerve F i b e r Loss and V i s u a l F i e l d Defect i n Glaucoma, Ischemic Neuropathy, Papilledema, and Toxic Neuropathy. A r c h . Ophthalmol. 100, 135-146. Randwal Instrument Company (1981) Model 33Y R e t i n a l A c u i t y  Instrument Aug.12,1981. Southbridge Ma. Regan,D. and Beverley,K. (1983) V i s u a l F i e l d s Described by Con t r a s t S e n s i t i v i t y , by A c u i t y , and by R e l a t i v e S e n s i t i v i t y t o D i f f e r e n t O r i e n t a t i o n s . Inv.  Ophthalmol, and V i s . S c i . 24(6), 754-759. Riggs,L. (1965) V i s u a l A c u i t y In. Graham,C. (ed.) V i s i o n  and V i s u a l P e r c e p t i o n . New York: J . Wiley and Sons,p.321-349. R i j s d i j k , J . , Rroon,J., and Van der Wildt,G. (1980) Contrast s e n s i t i v i t y as a f u n c t i o n of p o s i t i o n on the r e t i n a . V i s . Res., 20, 235-241 Ross,J., Bron,A. and Clarke,D. (1984) C o n t r a s t s e n s i t i v i t y and v i s u a l d i s a b i l i t y in c h r o n i c simple glaucoma. Br.  J . Ophthalmol. 68, 821-827. Ross,J., Bron,A. and Clarke,D. (1985) E f f e c t of Age on c o n t r a s t s e n s i t i v i t y f u n c t i o n : u n i o c u l a r and b i n o c u l a r f i n d i n g s . Br. J . Ophthal. 69(1), 51-56. Rovamo,J., V i r s u , V . , Laurinen,P., and Hyvarinen,L. (1982) R e s o l u t i o n of g r a t i n g s o r i e n t e d along and across meridians i n p e r i p h e r a l v i s i o n . I n v e s t . Ophthal. and  V i s . S c i . , 23(5), 666-670. Schade,0 (1956) O p t i c a l and P h o t o e l e c t r i c Analog of the Eye J . Opt. Soc. Am. 46(9), 721-739. Schade,0. (1958) On the Q u a l i t y of C o l o r - T e l e v i s i o n Images and the P e r c e p t i o n of Color D e t a i l . J . Soc. Motion  P i c t u r e and T e l e . Engineers 67(12), 801-819. Sekuler,R. and Hutman,L. (1980) S p a t i a l v i s i o n and aging I: c o n t r a s t s e n s i t i v i t y . Gerontology, 35(5) , 692-699. Sekuler,R. and Owsley,C. (1982) The s p a t i a l v i s i o n of o l d e r humans. In Sekuler.,R., K l i n e , D . , and Dismukes,K. (eds.) Aging and Human V i s u a l F u n c t i o n Alan R. L i s s , Inc.:New York,p.185-202. Sekuler,R., Hutman,L.,and Owsley,C. (1980) Human aging and s p a t i a l vision.. S cience, 209( 12), 1255-1256. Selwyn,E. (1948) The Photographic and V i s u a l R e s o l v i n g 1 03 Power of Lenses Part I. V i s u a l R e s o l v i n g Power. The  Photographic J o u r n a l S e c t i o n B 88B, 6-12. Skalka,H. (1980) E f f e c t of Age on Arden g r a t i n g a c u i t y . Br.  J . Ophthalmol. 64 21-23. Skalka,H. (1980a) Comparison of S n e l l e n a c u i t y , VER a c u i t y , and Arden g r a t i n g scores i n macular and o p t i c nerve d i s e a s e s . Br. J . Ophthalmol. 64 24-29. Skalka,H. (1984) L e t t e r to the E d i t o r s . V i s . Res. 24(9), 1115. Smith,T., Remijan,P., Remijan,W., Kolder,H., and Snyder,J. (1979) A new t e s t of v i s u a l a c u i t y using a hol o g r a p h i c phase g r a t i n g and a l a s e r . Arch. Ophthalmol., 97, 752-754. Sokol,S., Moskowitz,A., Skarf,B., Evans,R., Molitch,M. and Senior,B. (1985) Contrast S e n s i t i v i t y i n D i a b e t i c s With and Without Background Retinopathy. Arch.  Ophthalmol. 103(1), 51-54. Stone,J, Dreher,B. and Leventhal,A. (1979) H i e r a r c h i c a l and P a r a l l e l Mechanisms i n the O r g a n i z a t i o n of V i s u a l Cortex. B r a i n Res. Reviews 1, 345-394. Tagami,Y., Onuma,T., Kuniyoshi,M. and Isayama,Y (1980) Comparison of S p a t i a l C o n t r ast S e n s i t i v i t y with V i s u a l F i e l d i n O p t i c Neuropathy and Glaucoma. Doc.  Ophthalmol. Proc. S e r i e s . Vol.26 p.147-153. . Van der Horst,G. (1969) F o u r i e r A n a l y s i s and Color D i s c r i m i n a t i o n . J . Opt. Soc. Am. 59(12), 1670-1676. Van der Horst,G. and Bouman,M. (1969) Spatiotemporal C h r o m a t i c i t y D i s c r i m i n a t i o n . J . Opt. Soc. Am. 59(11), 1482-1488. Van Der W i l d t and Waarts,R. (1983) Contrast D e t e c t i o n and I t s Dependence on the Presence of Edges and L i n e s i n the Stimulus F i e l d . V i s . Res. 23(8), 821-830. Van Meeteren,A. and Vos,J. (1972) R e s o l u t i o n and Co n t r a s t S e n s i t i v i t y at Low Luminances. V i s . Res. 12, 825-833. Van Nes, F. and Bouman,M. (1967) S p a t i a l Modulation T r a n s f e r i n the Human Eye. J . Opt. Soc. Am. 57(3) 401-406. Vegan and H a l l i d a y , B . (1982) A f o r c e d - c h o i c e t e s t improves c l i n i c a l c o n t r a s t s e n s i t i v i t y t e s t i n g . Br. J . Ophthal.  66(8), 477-491. Watanabe,A., Mori,T., Nagata,S. and Hiwatashi,K. (1968) S p a t i a l Sine-wave Responses of the Human V i s u a l 1 04 System. V i s . Res. 8j_ 1245-1263. Woodhouse,J. (1975) The e f f e c t of p u p i l s i z e on g r a t i n g d e t e c t i o n at v a r i o u s c o n t r a s t l e v e l s . V i s . Res., 15, 645-648. Wright,M. (1982) Contrast s e n s i t i v i t y and a d a p t a t i o n as a f u n c t i o n of g r a t i n g l e n g t h . V i s . Res., 22, 139-149. Wright,M. and Johnston,A. (1983) Spatiotemporal Contrast S e n s i t i v i t y and V i s u a l F i e l d Locus. V i s . Res. 23(10), 983-989. Zulauf,M., Flammer,J., Chrenkova,A., S i g n e r , C , Lotmar,W. and Wetterwald,N. (1984) Der E i n f l u s s der S t r e i f e n r i c h t u n g von Interferenzmustern auf d i e K o n t r a s t e m p f i n d l i c h k e i t b e i Weissen und farbigem L i c h t . K l i n . Mbl. Augenheilk 184(5), 394-396. 1 05 APPENDIX ONE P h y s i o l o g i c a l Anatomical C o n t r i b u t i o n to Understanding of  S p a t i a l C o n t r a s t S e n s i t i v i t y That groups of r e c e p t o r s act in c o o p e r a t i o n with each other and respond to a stimulus d i f f e r e n t l y than an adjacent group of r e c e p t o r s has been demonstrated by the response of r e t i n a l g a n g l i o n c e l l axons in primates (macaque and rhesus monkey) and other mammals ( r a t , but p r i m a r i l y the cat and r a b b i t ) . Stephen K u f f l e r in the e a r l y 1950's i s c r e d i t e d with f i r s t r e c o r d i n g from the r e t i n a l ganglion c e l l bodies i n the i n t a c t cat eye. The i n s e r t e d m i c r o e l e c t r o d e s were able to r e c o r d the response of a c e l l to l o c a l i z e d spots of l i g h t i n the f i e l d of v i s i o n . He d i s c o v e r e d , among other t h i n g s , that each c e l l had a p a r t i c u l a r area i n the v i s u a l f i e l d t h a t evoked a response from the c e l l . A l i g h t o u t s i d e t h i s area caused no change i n the measured c e l l ' s b a s e l i n e f i r i n g r a t e . F u r t h e r , the response i n these s o - c a l l e d r e c e p t i v e f i e l d s was not uniform a c r o s s i t s e n t i r e area. The r e c e p t i v e f i e l d s were best d e s c r i b e d as c i r c u l a r and organized i n t o a n t a g o n i s t i c c o n c e n t r i c r i n g s . B a s i c a l l y two types were d i s t i n g u i s h e d based upon t h e i r response to a l i g h t in the center of the r e c e p t i v e f i e l d . Those that i n c r e a s e d t h e i r f i r i n g r a t e with the p r e s e n t a t i o n of the l i g h t were termed ON-center and those that decreased (below b a s e l i n e ) were OFF-center c e l l s . Conversely an OFF-center c e l l would i n c r e a s e i t s f i r i n g r a t e to decreased i l l u m i n a t i o n i n the center of i t s r e c e p t i v e f i e l d and an ON-center c e l l would decrease i t s f i r i n g r a t e to the same s t i m u l u s . The response of a model ON-center c e l l i s shown in F i g u r e 23. When micropettes were used i n s t e a d of the platinum e l e c t r o d e s used by K u f f l e r , c e l l s were uncovered that had s m a l l e r center r e c e p t i v e f i e l d s than those o r i g i n a l l y r e p o r t e d . F u r t h e r refinements and experiments with d i f f e r e n t r e c o r d i n g techniques r e v e a l e d s t i l l more d i v e r s i t y i n the f u n c t i o n i n g of r e t i n a l g a n g l i o n c e l l s . For example c e l l s t h a t had c o l o r -opponent r e c e p t i v e f i e l d s were observed as w e l l as some that responded maximally to a s t i m u l u s moving i n a c e r t a i n d i r e c t i o n . In a d d i t i o n , response of c e l l s i n the "higher" c e n t e r s , such as i n the v i s u a l c o r t e x , to a l i g h t stimulus were found to be even more complex. See Lennie (1980) and Stone e t . a l . (1979) for a much more i n depth d i s c u s s i o n of the p r o p e r t i e s of these c e l l s at a l l l o c a t i o n s i n the v i s u a l pathway. With the advent of these d i s c o v e r i e s and new techniques i n understanding the a c t i v i t y of the v i s u a l system, research i n t o the parameters a f f e c t i n g the f i r i n g of s i n g l e c e l l s g r e a t l y i n c r e a s e d . E n r o t h - C u g e l l and Robson, both r e s e a r c h e r s i n t e r e s t e d i n the f u n c t i o n i n g of the v i s u a l system, decided to j o i n f o r c e s and use the stimulus that Schade (1956) had then r e c e n t l y i n t r o d u c e d i n t o the study of human s p a t i a l v i s i o n and apply i t to study s i n g l e c e l l events i n r e t i n a l g a n g l i o n c e l l s . (Enroth-C u g e l l and Robson, 1984) T h i s s t i m u l u s , the s i n e g r a t i n g p a t t e r n p r e v i o u s l y d i s c u s s e d , l e d them to p u b l i s h what has now been d e s c r i b e d as "the most i n f l u e n t i a l statement about r e t i n a l g a n g l i o n c e l l s i n 30 y e a r s . " ( A l p e r n , 1984) 106 • centre i i I I ^. _ s « \ f ; i I f I I F i g u r e 23: A Model ON-center C e l l Responding to Changes i n I l l u m i n a t i o n W i t h i n i t s R e c e p t i v e F i e l d C e n t e r From E n r o t h - C u g e l l and Robson, 1984, p.254 1 07 In t h i s p u b l i c a t i o n ( E n r o t h - C u g e l l and Robson, 1966) they r e p o r t e d that both ON and OFF-center c e l l s c o u l d be c l e a r l y s u b d i v i d e d i n t o two groups based upon t h e i r response to a sine g r a t i n g p a t t e r n that was a l t e r n a t e l y presented with a uniformly i l l u m i n a t e d f i e l d of the same mean luminance as the s i n e g r a t i n g . For one group of c e l l s a p o s t i o n of the g r a t i n g p a t t e r n c o u l d be found so that no change i n b a s e l i n e f i r i n g r a t e was observed as the p a t t e r n and the uniform f i e l d were a l t e r n a t e d in time. T h i s p a t t e r n was presented over the e n t i r e r e c e p t i v e f i e l d of the c e l l and not j u s t i n the center or surround. The i n f o r m a t i o n t h e r e f o r e was d e s c r i b e d as being summated over the e n t i r e r e c e p t i v e f i e l d and these c e l l s - - c a l l e d 'X' t y p e — w e r e s a i d to e x h i b i t l i n e a r s p a t i a l summation. For the other group no p o s i t i o n of the g r a t i n g would r e s u l t i n s i l e n t exchange. These c e l l s — t e r m e d 'Y' t y p e — w e r e t h e r e f o r e n o n l i n e a r s p a t i a l summators. The behaviour of these two d i f f e r e n t f u n c t i o n a l groups i s shown in F i g u r e 24. A f t e r t h i s f u n c t i o n a l dichotomy became known, other p r o p e r t i e s of these two types were unearthed and c e l l s that d i d not appear to f i t c l e a r l y i n t o e i t h e r c ategory were d i s c o v e r e d . These were termed 'W c e l l s by Enroth-C u g e l l and Robson. Lennie (1980) termed t h i s grouping the 'W umbrella s i n c e so many d i f f e r e n t types are p laced i n t h i s c a t e g o r y . E v e r y t h i n g that i s not c l e a r l y X or Y i s c a l l e d W. Since t h i s work was done on the c a t , others have examined the behaviour of r e t i n a l c e l l s i n other mammals to see whether t h i s f u n c t i o n a l d i f f e r e n c e e x i s t e d . Of p a r t i c u l a r i n t e r e s t i s the f i n d i n g s i n the primate. Here g r o u p i n g — b y other r e s e a r c h e r s -was not i n t o X ,Y and W r a t h e r other l a b e l s were a p p l i e d . Since the behaviour of these c e l l s p a r a l l e l l e d that of the c a t ( i n the rhesus and macaque monkey at l e a s t ) the d i f f e r e n t t e r m i n o l o g i e s may be roughly equated. Given i n Table 11 are some of the p r o p e r t i e s of these c l a s s e s of c e l l s . X and Type I are roughly equal as are Y and Type III and IV. Type II and Vb would probably be c a l l e d W type. Of p a r t i c u l a r i n t e r e s t i s the f a c t that these c e l l s may r e c e i v e inputs from d i f f e r e n t cone types, some being i n h i b i t o r y and others f a c i l i t o r y . (de Monasterio, 1978,a,b,c) Type IV, f o r example, was found to have c e n t e r s with i n p u t s from two or three types of cones and surrounds with i n p u t s from u s u a l l y only the red type. (His red type were those with maximal s e n s i t i v i t y between 570-580 nm.) In a d d i t i o n i t was found that r e t i n a l g a n g l i o n c e l l s e x h i b i t e d s p a t i a l frequency tuning, that i s , f o r d i f f e r e n t c e l l s an o p t i m a l s p a t i a l frequency c o u l d be found that e l i c i t e d the g r e a t e s t f i r i n g r a t e of the c e l l . 108 F i g u r e 24: F i r i n g r a t e Records from a Cat R e t i n a l O FF-center X - c e l l ( l e f t ) and an ON-center Y - c e l l ( r i g h t ) Responding to the Appearance and Disap p e a r a n c e of a Sine-wave G r a t i n g i n D i f f e r e n t P o s i t i o n s . The p i c t u r e s i n the midd l e show the p o s i t i o n s of the s t i m u l u s p a t t e r n i n r e l a t i o n to the r e c e p t i v e f i e l d d u r i n g the p e r i o d i n which the p a t t e r n was p r e s e n t (1.1 s e c . of ev e r y 2.2 s e c . as marked by the bar under each r e c o r d ) . When the p a t t e r n d i s a p p e a r e d the s t i m u l u s s c r e e n remained a t the same mean luminance. The v e r t i c a l bar -corresponds to a f i r i n g r a t e of 100 i m p u l s e s / s e c . C — n n r~ o -•• C 3 3 (t> Q W n W C r4 3 < 3 r+ r* • ra w O n ' — * (0 , -1 01 3 "0 - Q "J • o n — 0 ~ ro O U i (D TJ (J -J ro <o < — O - i t ) n - J m ro — a *< m (D "O n ro ro n n O n tu ro ra 3 w n n c a - l o ra n c T i n (tut WO (D — C C (J 3 O < — ra "o ra tu n 3 w < c 3 n « "O 3 "O r+ tu cu <-* in :r u, ro w ^ M n c o w • 3" *+ o 3 3 o CT C - T3 u> - n o o « •raw 3 n 3 3 UI CD IfJ I o ra r* — a i ra a < 3 i 3 ra - < • o -•> c N . -*» n — *^ at • o -• o ** i o ID 1 10 APPENDIX TWO Comparison of Th r e s h o l d Determination f o r S p a t i a l CSF. Method of  Constant S t i m u l i versus Method of I n c r e a s i n g Contrast Method Stimulus c o n d i t i o n s were i d e n t i c a l to that in the Method s e c t i o n (see p.65-68) except i n the method of p r e s e n t a t i o n of the t a r g e t . The 19 year o l d female viewed v e r t i c a l sine g r a t i n g p a t t e r n s at each s p a t i a l frequency as f o l l o w s : Time A ascending method of l i m i t s ( a l s o c a l l e d method of i n c r e a s i n g c o n t r a s t ) to 15, 10, 7.5, 6, 3, 1.5, .75 cyc/deg. Time B constant s t i m u l i (modulation depth set at .01 then presented to observer, i f not seen then t a r g e t removed from s i g h t and p a t t e r n i n c r e a s e d i n modulation by 1 u n i t . T h i s procedure was repeated u n t i l p a t t e r n c o u l d be detected) to 15, 10, 7.5, 6, 3, 1.5, .75 cyc/deg. SHORT REST Time C repeat procedure from Time A Time D repeat procedure from Time B R e s u l t s Threshold v a l u e s obtained i n Time A and Time C were used to c a l c u l a t e an a r i t h m e t i c mean rawscore t h r e s h o l d value f o r ascending method of l i m i t s at each s p a t i a l frequency. S i m i l a r i l y , v a l u e s obtained i n Time B and Time D were used to o b t a i n mean t h r e s h o l d v a l u e s f o r the method of constant s t i m u l i . Dependent sample T - t e s t s were computed f o r each s p a t i a l frequency. H i g h l y s i g n i f i c a n t d i f f e r e n c e s were noted i n c o n t r a s t t h r e s h o l d at each s p a t i a l frequency between the two methods. At a l l s p a t i a l f r e q u e n c i e s the method of constant s t i m u l i r e a l i z e d s i g n i f i c a n t l y lower c o n t r a s t t h r e s h o l d values (higher c o n t r a s t s e n s i t i v i t y ) than the method of i n c r e a s i n g c o n t r a s t . (9df. p>.001) C o n t r a s t s e n s i t i v i t y f u n c t i o n s f o r these two methods are given i n F i g u r e 25. C l e a r l y method of s t i m u l u s p r e s e n t a t i o n / t h r e s h o l d determination w i l l i n f l u e n c e the c o n t r a s t s e n s i t i v i t y f u n c t i o n . I l l F i g u r e 25: C o n t r a s t S e n s i t i v i t y Methods of T h r e s h o l d D e t e r m i n a t i o n F u n c t i o n For Two 1 1 2 APPENDIX THREE Machine Used to Test S p a t i a l Contrast S e n s i t i v i t y i n t h i s -Experiment The Randwal Model 33Y R e t i n a l A c u i t y Instrument--the apparatus used in the f o l l o w i n g experiment--was o r i g i n a l l y designed to a i d in the assessment of v i s u a l f u n c t i o n in i n d i v i d u a l s with reduced v i s i o n that was f e l t to be p r i m a r i l y caused by c o r n e a l or l e n t i c u l a r o p a c i t y . Since the l i g h t source employed was a helium-neon l a s e r ( Xd=632.8 nm. Smith e t . a l . , 1979), i t c o u l d penetrate many o p a c i t i e s that would block other sources. T h i s a b i l i t y seems to stem mainly from the coherent beam that i s produced by l a s e r s and the f a c t that the small p i n s of l i g h t produced by the l a s e r (under 2mm.) can be p o s i t i o n e d so that they do not pass through the densest part of a lens o p a c i t y . When examining c a t a r a c t p a t i e n t s ' v i s u a l a c u i t y with t h i s machine, i t i s not unusual f o r an i n d i v i d u a l who claimed to have only l i g h t p e r c e p t i o n or f i n g e r counting to be able to c o r r e c t l y i d e n t i f y a p a t t e r n with a S n e l l e n e q u i v a l e n c y of even 20/40. Of course t h i s machine w i l l not penetrate very dense c a t a r a c t s nor can one circumvent c a t a r a c t s that are too l a r g e even when the p u p i l i s d i l a t e d to i t s f u l l e s t extent ( i n the region of 8mm. diameter). A l s o , l a r g e amounts of d e b r i " f l o a t e r s " i n the v i t r e o u s w i l l cause shadows to appear on the imaged p a t t e r n on the r e t i n a as w e l l as s c a t t e r i n g the l i g h t . ( F u l l e r and Hutton, 1982) T h i s moving mass (mess) i s o f t e n r e p o r t e d by s u b j e c t s e s p e c i a l l y at .01 c o n t r a s t v a l u e s (that i s , when the t e s t f i e l d appears homogenous). This phenomenon probably a l s o i s a f u n c t i o n of i m p e r f e c t i o n s i n the l a s e r i t s e l f . S l i g h t i m p e r f e c t i o n s i n the c o n s t r u c t i o n of the l a s e r such as i m p e r f e c t i o n s i n the alignment of the m i r r o r s at the ends of the l a s e r c a v i t y or of t h e i r s u r f a c e s or that of the Brewster window could a l l c o n t r i b u t e to a beam with a l e s s than uniform i r r a d i a n c e d i s t r i b u t i o n . These i m p e r f e c t i o n s can a l s o cause the emitted beam to be l e s s than p e r f e c t l y coherent and to i n t e r f e r e with i t s e l f r e s u l t i n g i n these luminance d i s c o n t i n u i t i e s . (Francon, 1979) That some people i n d i c a t e the presence of t h i s more than ot h e r s may i n d i c a t e that both f a c t o r s — - m i s c o s c o p i c i n t e r f e r e n c e and v i t r e a l d e b r i - - a r e c o n t r i b u t i n g to the observed "speckle." Even though the e f f i c a c y of t h i s machine as a p r e d i c t i v e t e s t i n c a t a r a c t i s p r e s e n t l y disputed' i n the l i t e r a t u r e ( i t s c l i n i c a l v a l i d i t y i s beyond the scope of t h i s paper), there appears to be no c o n t e n t i o n that t h i s machine's imaged p a t t e r n i s - - f o r a l l i n t e n s i v e p u r p o s e s — u n e f f e c t e d by the r e f r a c t i v e power of the eye being t e s t e d . I t i s u n e f f e c t e d as long as the eye examined i s not ametropic by ±10 d i o p t e r s or more. This i s brought about by using a p h y s i c a l l y small l i g h t source and a v i r t u a l image. Smith e t . al.,'1979, p. 752 s t a t e i t more s t r o n g l y : "using a Maxwellian view to n u l l i f y the r e f r a c t i v e power of the eye." In the instrument manual that accompanies the model 33Y i t 1 1 3 i s claimed that f o r the 5 and 8 degree f i e l d s i z e s " . . . . d i s t o r t i o n of the t a r g e t boundary should be i n s i g n i f i c a n t , even i n the presence of a 15 to 20 d i o p t e r r e f r a c t i v e e r r o r . " (Randwal, 1981) T h i s c o n c l u s i o n no doubt i s based upon c a l c u l a t i o n s i n geometrical o p t i c s . H a l l i d a y and Ross (1983) e x p e r i m e n t a l l y examined the r e s i s t a n c e of the 33Y to r e f r a c t i v e e r r o r - - d e f o c u s i n g i n t h e i r t e r m i n o l o g y — b y p l a c i n g t r i a l l e n s es of v a r y i n g d i o p t e r s i n f r o n t of two eyes each from a separate s u b j e c t . C y c l o p l e g i a was induced by 1% e y e l o p e n t o l a t e and then e i t h e r h o r i z o n t a l or v e r t i c a l g r a t i n g s of v a r y i n g s p a t i a l frequency were viewed through the randomly chosen t r i a l l e n s e s . A f t e r each c o r r e c t i d e n t i f i c a t i o n of p a t t e r n o r i e n t a t i o n a f i n e r g r a t i n g was shown. An i n c o r r e c t response was followed by a p a t t e r n of a c o a r s e r s p a t i a l frequency. The values of 8 such r e v e r s a l s were averaged to g i v e a r e t i n a l a c u i t y f o r that l e n s . No decrement i n a c u i t y was found with d e f o c u s i n g . A f t e r the instrument was f i r s t i ntroduced (see Smith e t . a l . , 1979) a l a t e r m o d i f i c a t i o n enabled c o n t r a s t to be v a r i e d from 1 to .01. T h i s permitted the d e t e r m i n a t i o n of c o n t r a s t s e n s i t i v i t y values and the d e r i v a t i o n of c o n t r a s t s e n s i t i v i t y f u n c t i o n s . In the new v e r s i o n of the apparatus, the l a s e r beam i s s p l i t i n t o three two of which are recombined t o form the i n t e r f e r e n c e p a t t e r n while the t h i r d beam serves to vary the c o n t r a s t of the f r i n g e s formed by d e s t r u c t i v e i n t e r f e r e n c e between the other two beams. Using only one source e l i m i n a t e s d i f f i c u l t i e s i nherent i n c r e a t i n g one p a t t e r n from s e v e r a l l i g h t sources. In the l a s e r i n t e r f e r o m e t e r u t i l i z e d i n the present study, f o r example, mean p a t t e r n luminance when measured p h o t o m e t r i c a l l y was observed to remain r e l a t i v e l y c o n s t a n t - - t h a t i s w i t h i n the l i m i t a t i o n s of measurement e r r o r — w i t h change in modulation depth of the sine p a t t e r n . It appears t h e r e f o r e that t h i s device can be r e a l i s t i c a l l y c o n sidered to t e s t s p a t i a l c o n t r a s t s e n s i t i v i t y . One should note that a s t i l l l a t e r v e r s i o n of t h i s instrument c l e a n s up the sometimes d i s t u r b i n g l a s e r speckle by "...passing the background beam through some a d d i t i o n a l o p t i c s and a r o t a t i n g ground g l a s s . The e x i s t i n g l a s e r s p e c k l e i s s p a t i a l l y averaged over a time i n t e r v a l of about one microsecond and the p a t i e n t sees a p e r f e c t l y uniform background." (Remijan, P. p e r s o n a l communication) 1 1 4 APPENDIX FOUR LETTER OF CONSENT Comparison of Contrast S e n s i t i v i t y between Younger and Older Observers by Dr. S.M. Drance, Dr. R. Lakowski, and H. Dahl I, the undersigned, have been f u l l y informed of the nature and extent of my p a r t i c i p a t i o n i n the measurement of my v i s u a l a c u i t y by l a s e r i n t e r f e r o m e t r y . I understand t h a t I w i l l not be subj e c t e d to any discomfort or abnormal e f f o r t and that the r e s u l t s w i l l be h e l d i n s t r i c t e s t c o n f i d e n c e by Dr. S. M. Drance, Dept. of Ophthalmology. My p e r s o n a l r e s u l t s w i l l be a v a i l a b l e to me on request and can be made p u b l i c only in an anonymous form with the r e s u l t s from the other s u b j e c t s i n t h i s study. I w i l l be requested to detec t the presence of a red and black fuzzy bar p a t t e r n that emerges from an homogenous red c i r c l e . T h i s w i l l r e q u i r e approximately 1/2 hour of my time. I a l s o r e a l i z e t h a t I may withdraw from t e s t i n g at any time or that I may r e f u s e to p a r t i c i p a t e without p r e j u d i c i n g myself i n any way. I agree to p a r t i c i p a t e i n t h i s experiment and acknowledge r e c e i p t of a copy of t h i s consent form: s i g n a t u r e witness date 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0096489/manifest

Comment

Related Items