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An examination of age-related changes in achromatic and chromatic retinal increment thresholds at photopic… Hancock, Sherri Rosemary McDonald 1990

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A N E X A M I N A T I O N OF A G E - R E L A T E D CHANGES I N A C H R O M A T I C AND CHROMATIC R E T I N A L INCREMENT THRESHOLDS AT P H O T O P I C L E V E L S b y S h e r r i R o s e m a r y M c D o n a l d H a n c o c k B . S c , T h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1986 A T H E S I S S U B M I T T E D I N P A R T I A L F U L F I L L M E N T FOR THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n THE F A C U L T Y OF GRADUATE S T U D I E S D e p a r t m e n t o f P s y c h o l o g y We a c c e p t t h i s t h e s i s a s c o n f o r m i n g t o t h e r e q u i r e d s t a n d a r d THE U N I V E R S I T Y OF B R I T I S H C O L U M B I A A u g u s t 1990 © S h e r r i R o s e m a r y M c D o n a l d H a n c o c k , 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Psychology The University of British Columbia Vancouver, Canada Date August 31, 1990.  DE-6 (2/88) i i A b s t r a c t This r e s e a r c h i n v e s t i g a t e d the i n f l u e n c e of the normal aging process on t r u l y photopic achromatic and chromatic r e t i n a l increment t h r e s h o l d over an extensive range of c o l o r e d t a r g e t s . I t was found that f o r both achromatic and chromatic r e t i n a l t h r e s h o l d s there i s a s i g n i f i c a n t c o r r e l a t i o n between advancing age and the s t i m u l u s luminance i n t e n s i t y at t h r e s h o l d across the v i s i b l e spectrum. This c o r r e l a t i o n i s g r e a t e r for the s h o r t wavelength range than f o r both the middle and the long wavelength ranges ( r ^ (achromatic)= 0.43; (chromatic) = 0.49. In a d d i t i o n , a small e x p l o r a t o r y study was completed which examined the r o l e of p r e r e c e p t o r a l changes i n these a g e - r e l a t e d d i f f e r e n c e s i n c o l o r v i s i o n f u n c t i o n . Results from t h i s p r e l i m i n a r y study (Experiment II) support the s u p p o s i t i o n t h a t p r e r e c e p t o r a l f a c t o r s cannot account for a l l of the a g e - r e l a t e d l o s s e s that are seen i n v i s u a l f u n c t i o n , p a r t i c u l a r l y i n the middle and long wavelength ranges of the v i s i b l e spectrum. i l l Table of Contents Page A b s t r a c t s i i L i s t of F i g u r e s v L i s t of Tables v i i L i s t of Appendices v i i i Acknowledgements i x I n t r o d u c t i o n 1 I. A H i s t o r y of S t u d i e s on Color V i s i o n and Aging... 4 A. T r a d i t i o n a l Tests of Color V i s i o n 5 B. R e t i n a l Increment Threshold Studies 10 C. Studies on the Role of P r e r e c e p t o r a l F a c t o r s 14 (1) P h y s i o l o g i c a l changes i n the l e n s . . . . 14 (2) The study of aphakic observers 15 (3) S i m u l a t i o n of a g e - r e l a t e d lens changes 17 (4) F a c t o r i n g out e f f e c t s of lens changes 18 I I . T h e o r e t i c a l P e r s p e c t i v e s on R e t i n a l Increment Threshold Measurements 21 I I I . M e t hodological C o n s i d e r a t i o n s f o r the Present Study 24 (1) Photopic a d a p t a t i o n f i e l d 24 (2) Target s t i m u l i 25 (3) V i s u a l a c u i t y 26 (4) P u p i l s i z e 26 IV. P r o p o s a l 27 O b j e c t i v e s 27 Experiment I 27 Experiment II 28 Hypotheses . 29 Experiment I 29 Experiment II 30 Method 30 Apparatus 30 Perimeter 30 Background Luminance 33 Target Luminance 34 F l i c k e r 35 Photometer 36 Subjects 36 General 36 Experiment I 37 Recruitment 37 Experiment II 39 iv Procedures 39 General 39 Experiment 1 40 Experiment II 40 Testing Session 40 General 40 Experiment II 42 Data Conversion 46 Experimental Design 47 Experiment 1 47 Experiment II 48 Results 49 Experiment 1 49 Achromatic Data 50 Graphical Analysis 50 Group Average Data 57 D i s t r i b u t i o n within each group 61 Standard deviations of group data 65 F l i c k e r versus Color D i s t i n c t i o n 70 Chromatic Data 74 Graphical Analysis 74 Group Average Data 74 D i s t r i b u t i o n within each group.....'.... 77 Achromatic and Chromatic Data 77 S t a t i s t i c a l Analysis 77 Experiment II 82 Achromatic Data 85 Graphical Analysis... 85 Chromatic Data •••• 91 Graphical Analysis 91 Discussion 91 Data D i s t r i b u t i o n 98 Methodological Issues 100 Flicker/Color D i s t i n c t i o n 100 Attention Factors 103 Sample Selection 104 Sex Differences 104 Normal Aging Population '.. 105 Role of Prereceptoral Factors 106 References 107 V L i s t of Figures Figure Page 1. Relative spectral energy d i s t r i b u t i o n of C L E . Illuminant C and the Xenon-arc 32 2. Subject d i s t r i b u t i o n by age and sex 38 3 (a). Measured op t i c a l densities of human lenses across the v i s i b l e spectrum for four ages 45 3 (b). Optical densities of age simulation f i l t e r s across the v i s i b l e spectrum for four ages and a 0.50 neutral density f i l t e r 45 4 (a - g). Data d i s t r i b u t i o n within each individual age group for achromatic r e t i n a l increment thresholds 51 5. Data d i s t r i b u t i o n for group average data for achromatic r e t i n a l increment thresholds 60 6 (a - g). Group average data with standard deviation error bars included 66 7. Separation of color and f l i c k e r thresholds under achromatic testing conditions for 75 year old male subject 72 8. Separation of color and f l i c k e r thresholds under achromatic testing conditions for the extreme short wavelength stimuli 73 9. Data d i s t r i b u t i o n for group average data for chromatic r e t i n a l increment thresholds 75 10 (a - g). Data d i s t r i b u t i o n within each individual age group for chromatic r e t i n a l increment thresholds 78 11. Age correlations with wavelength across the v i s i b l e spectrum 83 12. Age correlations with short, middle and long wavelength stimuli 84 13 (a - j ) . Achromatic r e t i n a l increment thresholds for Experiment I I . A l l f i l t e r conditions are included for Subject 2. Conditions 3 and 4 are included for the other two subjects 86 v i 14 (a - j ) . Chromatic r e t i n a l increment t h r e s h o l d s for Experiment I I . A l l f i l t e r c o n d i t i o n s are i n c l u d e d f o r Subject 2. C o n d i t i o n s 3 and 4 are i n c l u d e d f o r the other two s u b j e c t s 93 v i i L i s t of Tables Table 1 D i s t r i b u t i o n of Subjects by Sex for each Group. 38 2 Average ages of the Subjects in each Group 38 3 The F i l t e r Simulation Conditions for Experiment II 67 v i i i L i s t of Appendices Appendix A. L i s t of F i l t e r s 110 Appendix B. Personal Health History I l l Appendix C. Age-simulation F i l t e r s 113 i x Acknowledgements I would f i r s t l i k e to thank my s u p e r v i s o r , Dr. Lakowski f o r h i s guidance, e x p e r t i s e , and encouragement during my time i n the v i s u a l l a b . His understanding of v i s u a l research i s t r u l y remarkable and I have gained a great d e a l from our p r o j e c t s together but I have learned even more from our informal d i s c u s s i o n s . Many thanks are extended to the members of my committee, Dr. S. Coren and Dr. B. deVr i e s f o r t h e i r v a l u a b l e c o n t r i b u t i o n s i n the p r e p a r a t i o n of t h i s manuscript. G r a t i t u d e i s a l s o o f f e r e d to the s u b j e c t s who p a r t i c i p a t e d i n t h i s study. T h i s t e s t i n g i s very demanding and time consuming. Many people gave generously of themselves and t h e i r time to a s s i s t i n the c o l l e c t i o n of t h i s data and without them, t h i s p r o j e c t would not have been p o s s i b l e . S p e c i a l thanks are a l s o extended to 3 d e d i c a t e d s u b j e c t s who spent many hours i n f r o n t of the perimeter f o r the repeated t e s t i n g r e q u i r e d for experiment I I ; Catherine Wall, Kara McCulloch and Gavin Dry. I would l i k e to extend a s p e c i a l thanks to the members of the v i s u a l l a b ; to P i e r s Samson f o r h i s help with the data e n t r y and the recruitment of h i s f a m i l y and f r i e n d s as s u b j e c t s , to Ronnie Lakowski J r . for h i s i n v a l u a b l e work on the computer programs, data analyses, and gr a p h i c s and f i n a l l y to L i b o r Vlcek f o r h i s f r i e n d s h i p , support and p h i l o s o p h i c a l c h a l l e n g e s . A warm thank you i s o f f e r e d to Carole Bishop f o r her a s s i s t a n c e with the format of t h i s manuscript and f o r her enthusiasm and p e r s p e c t i v e . A v e r y s p e c i a l thanks i s given to my f a m i l y f o r t h e i r continued understanding and support throughout t h i s time. They have always been a source of s t r e n g t h . F i n a l l y , my deepest g r a t i t u d e and a f f e c t i o n i s o f f e r e d to J e f f S u therland f o r h i s unwavering support, s e n s i t i v i t y and encouragement throughout t h i s endeavor. I AN EXAMINATION OF AGE-RELATED CHANGES IN ACHROMATIC AND CHROMATIC RETINAL INCREMENT THRESHOLDS AT PHOTOPIC LEVELS. I n t r o d u c t i o n The aging process i s a u n i v e r s a l experience and yet i t i s a l s o a h i g h l y i n d i v i d u a l e x p e r i e n c e . These f a c t s make the study of the aging process at once i n t r i g u i n g and c h a l l e n g i n g . In a d d i t i o n , the study and understanding of senescence becomes even more important and immediate as our p o p u l a t i o n base moves towards a g r e a t e r percentage of aged i n d i v i d u a l s . Much of the experimental study of aging focuses on how the aging process a f f e c t s an i n d i v i d u a l ' s a b i l i t y to f u n c t i o n e f f e c t i v e l y i n t h e i r environment. The v i s u a l system p l a y s a q u i n t e s s e n t i a l r o l e i n the human experience and our a b i l i t y to i n t e r a c t with the environment. An understanding of the a g e - r e l a t e d changes i n v i s u a l f u n c t i o n and the impact that they have on everyday f u n c t i o n i n g , t h e r e f o r e , i s of p a r t i c u l a r i n t e r e s t and importance f o r the study of the aging human organism. Within the context of aging r e s e a r c h , there i s no c l e a r consensus on a d e f i n i t i o n of or t h e o r e t i c a l p e r s p e c t i v e on agi n g . However, a good working d e f i n i t i o n has been p r o f f e r e d by B i r r e n and Schaie (1976): Aging r e f e r s to the r e g u l a r changes that occur i n mature, g e n e t i c a l l y r e p r e s e n t a t i v e organisms l i v i n g under r e p r e s e n t a t i v e environmental c o n d i t i o n s as they advance i n c h r o n o l o g i c a l age. T h i s i s an e f f e c t i v e general d e f i n i t i o n of aging because i t does not imply b i o l o g i c a l , environmental or s o c i a l c a u s a l i t y . I t a l s o a l l o w s f o r the c o n s i d e r a t i o n of both incremental and decremental changes i n f u n c t i o n . A f u r t h e r d e f i n i t i o n a l c o n s i d e r a t i o n i s that of what c o n s t i t u t e s normalcy. That i s , which changes c o n s t i t u t e normal senescence and which ones c o n s t i t u t e pathology. T h i s i s not a t r i v i a l d i s t i n c t i o n and not one that w i l l be e a s i l y r e s o l v e d . For example, many disease processes become more p r e v a l e n t with advancing age and are o f t e n r e f e r r e d to as a g e - r e l a t e d d i s e a s e s (e.g., glaucoma, c a t a r a c t s ) . The dilemma then becomes, at what point should a c o n d i t i o n which a f f e c t s a l a r g e group of e l d e r l y people be c o n s i d e r e d p a r t of the normal range of the aging process? Because of t h i s u n c e r t a i n d i s t i n c t i o n , i t i s important to c l e a r l y e s t a b l i s h the range of the aging experience t h a t i s to be s t u d i e d . T h i s may be accomplished by s t a t i n g a c l e a r c r i t e r i o n of normalcy. The i n t e n t i o n of the present study i s to examine the range of a g e - r e l a t e d changes i n c o l o r v i s i o n f u n c t i o n ( i . e . , photopic s p e c t r a l s e n s i t i v i t i e s ) w i t h i n the normal aging p o p u l a t i o n . For the purposes of t h i s study then, normalcy w i l l be d e f i n e d with respect to the absence of any known p a t h o l o g i c a l c o n d i t i o n , ocular (e.g., c a t a r a c t s ) or systemic (e.g., d i a b e t e s m e l l i t u s ) , that i s known to d i r e c t l y e f f e c t v i s u a l performance. It i s , t h e r e f o r e , assumed t h a t any changes i n v i s u a l f u n c t i o n that are found may be a s c r i b e d to a n o n - d i s e a s e - r e l a t e d aging p r o c e s s . That i s , i t w i l l i n d i c a t e an a l t e r a t i o n that i s w i t h i n the normal range of aging change i n the v i s u a l system. I t i s p o s s i b l e to d i v i d e the v i s u a l system i n t o three l e v e l s or l o c i of change; p r e r e c e p t o r a l , r e c e p t o r a l and p o s t r e c e p t o r a l . Any changes to s t r u c t u r e s that are proximal to the r e t i n a l r e c e p t o r s c o n s t i t u t e p r e r e c e p t o r a l changes. These i n c l u d e s e n i l e meiosis ( i . e . , a decrease i n the p u p i l l a r y a r e a ) , l e n t i c u l a r changes ( i . e . , o p a c i f i c a t i o n and d i s c o l o r a t i o n of the c r y s t a l l i n e lens) and macular changes ( i . e . , accumulation of macular pigment). R e c e p t o r a l changes i n v o l v e m o d i f i c a t i o n s to the i n t e g r i t y or f u n c t i o n i n g of the r e t i n a l r e c e p t o r s ( i . e . , rods and cones) and/or t h e i r concomitant pigments. P o s t r e c e p t o r a l changes i n c l u d e a l t e r a t i o n s i n neural s t r u c t u r e s and i n nerve co n d u c t i o n . Research has attempted to e s t a b l i s h the degree to which a g e - r e l a t e d changes i n v i s u a l f u n c t i o n can be a s c r i b e d to p r e r e c e p t o r a l changes or to r e c e p t o r a l changes or even p o s t r e c e p t o r a l changes. E a r l y i n the development of t h i s area of r e s e a r c h and f o r many years, the dominant p e r s p e c t i v e i n the f i e l d was based on Weale's assumption t h a t a l l of the observed a g e - r e l a t e d v i s u a l l o s s e s c o u l d be e x p l a i n e d by changes i n the o c u l a r media transparency and p u p i l s i z e ( i . e . , p r e r e c e p t o r a l changes) (1959, 1963). In 1962, Lakowski p r o f f e r e d data which i n d i c a t e d that l e n t i c u l a r changes co u l d not account f o r a l l of the age-r e l a t e d d i f f e r e n c e s i n c o l o r v i s i o n f u n c t i o n . More r e c e n t l y , s e v e r a l r e s e a r c h e r s have addressed t h i s issue (Johnson et a l , 1988; Haegerstrom-Portnoy et a l , 1989) and attempted to s e p a r a t e l y assess the r o l e s of p r e r e c e p t o r a l and r e c e p t o r a l changes. They a l s o found t h a t p r e r e c e p t o r a l changes d i d not s u f f i c i e n t l y account f o r a l l of the v i s u a l f u n c t i o n changes. Although i t i s now g e n e r a l l y accepted that p r e r e c e p t o r a l changes alone do not adequately e x p l a i n a l l of the f u n c t i o n a l changes, the c o n t r i b u t i o n made by each locus of change i s s t i l l u n c l e a r . I. A H i s t o r y of Studies on Color V i s i o n and Aging The formal study of senescent changes i n c o l o r v i s i o n began l e s s than 60 years ago. Many of the e a r l y s t u d i e s on the r e l a t i o n s h i p between age and c o l o r v i s i o n had focused on the developmental changes i n c o l o r v i s i o n a b i l i t i e s i n c h i l d r e n and young a d u l t s and d i d not examine changes i n the a d u l t or senescent v i s u a l system. The primary purpose of the e a r l y s t u d i e s i n v o l v i n g a d u l t s was to e s t a b l i s h whether or not there a c t u a l l y were any changes i n c o l o r v i s i o n a b i l i t y as a f u n c t i o n of advancing age. L a t e r r e s e a r c h became embroiled in a debate over c o n t r a d i c t o r y f i n d i n g s . T h i s h i s t o r i c a l survey w i l l be presented c h r o n o l o g i c a l l y and w i l l b r i e f l y d e s c r i b e some of the important parameters of the s t u d i e s such as subject v a r i a b l e s (e.g., age, gender), the number of s u b j e c t s 5 tested, testing procedures used, and the conclusions drawn by the authors. It w i l l be divided into 3 groups of studies, those that u t i l i z e d t r a d i t i o n a l color v i s i o n tests, those that u t i l i z e d increment spectral s e n s i t i v i t y measurements (including achromatic, chromatic and color increment threshold functions) and those which s p e c i f i c a l l y examined the contribution of prereceptoral factors in the color v i s i o n changes. A. T r a d i t i o n a l Tests of Color Vision Henry Clay Smith was the f i r s t to study the rela t i o n s h i p of color v i s i o n and age for an adult population. The results were reported in 1943, although some of th i s work had actually been completed some years e a r l i e r as part of his doctoral t h e s i s . He had studied color v i s i o n a b i l i t y over the life s p a n ( i . e . , subjects from 5 to 87 years of age, N= 51) and found that color discrimination a b i l i t y improved r a p i d l y from early childhood, through adolescence and was the best at approximately 25 years of age. Smith also reported that there was l i t t l e or no loss in color discrimination during the middle age group (30 to 64 years) but that there was a substantial loss in the older group (over 65 years). Unfortunately, this study only involved 19 subjects in the middle age group. He concluded that color discrimination a b i l i t i e s varied with age in a sim i l a r manner to those of f l u i d i n t e l l i g e n c e and that the losses in color 6 d i s c r i m i n a t i o n were probably p r i m a r i l y due to changes i n a t t i t u d e and l e a r n i n g r a t h e r than to changes i n v i s u a l r e c e p t o r p hysiology. T h i s c o n c l u s i o n f i t w e l l with the assumptions pr e v a l e n t at that time i n aging r e s e a r c h . That i s , aging r e s u l t s i n decrements i n c e n t r a l processes which a f f e c t performance on many t a s k s . T i f f i n reported on a l a r g e s c a l e study of c o l o r v i s i o n and aging i n 1942. He had t e s t e d the c o l o r v i s i o n of 7000 f a c t o r y workers using a 4-item c o l o r v i s i o n t e s t . He r e p o r t e d that 26 per cent of the young s u b j e c t s and 68 per cent of the s u b j e c t s over 55 years of age had a reduced c o l o r d i s c r i m i n a t i o n a b i l i t y . T h i s i n d i c a t e d that there i s a dramatic decrease i n the a b i l i t y to d i s c r i m i n a t e c o l o r s with advancing age, but t h a t there are a l s o s u b s t a n t i a l l o s s e s even i n the younger groups. These r e s u l t s were s i m i l a r to those rep o r t e d by Lawshe (1948) but were c o n t r a r y to those reported by Smith i n 1943. Boice, Tinker and Paterson (1948) were c r i t i c a l of T i f f i n ' s study on s e v e r a l l e v e l s i n c l u d i n g the q u e s t i o n a b l e v a l i d i t y of the 4-item c o l o r v i s i o n t e s t (e.g., i t y i e l d e d a higher than normal f a i l u r e r a t e f o r young observers) and the lack of c o n t r o l for s u b j e c t v a r i a b l e s such as i n t e l l i g e n c e and socioeconomic s t a t u s . They t e s t e d a r a t h e r homogeneous group of 236 s u b j e c t s with 2 t e s t s f o r c o l o r v i s i o n d e f i c i e n c i e s . They found no s u b s t a n t i a l l o s s i n c o l o r d i s c r i m i n a t i o n u n t i l 60 years of age, a f t e r which p o i n t 25 per cent of these s u b j e c t s were found to have poorer than 7 normal c o l o r d i s c r i m i n a t i o n . These r e s u l t s were i n d i r e c t c o n f l i c t with those of T i f f i n but s i m i l a r to those of Smith. In 1950, Chapanis t e s t e d a la r g e sample of s u b j e c t s from ages 7 to 77 years on 5 pseudoisochromatic p l a t e (PIC) t e s t s i n c l u d i n g the I s h i h a r a Test f o r Colour B l i n d n e s s and the Dvorine Colour D i s c r i m i n a t i o n Screening T e s t . He found a s l i g h t p o s i t i v e c o r r e l a t i o n between age and the s c o r e s on the c o l o u r v i s i o n t e s t s . When the subj e c t s under 15 years were removed from the p o o l , however, t h i s r e l a t i o n s h i p dropped to zero which i n d i c a t e s that the a d u l t s tended to perform b e t t e r on these t e s t s than the c h i l d r e n d i d . In a d d i t i o n , the older s u b j e c t s i n the study showed no decrement i n t h e i r s c o r e s on these colour v i s i o n t e s t s . Chapanis a l s o examined the r e l a t i o n s h i p between age, v i s u a l a c u i t y and c o l o r v i s i o n . He concluded that, although there was s l i g h t evidence of a p o s i t i v e r e l a t i o n s h i p between v i s u a l a c u i t y and the scores on the colour v i s i o n t e s t s (the c o r r e l a t i o n s were very s m a l l ) , the e r r o r s made on these pseudo-isochromatic p l a t e s d i d not r e s u l t from minor l o s s e s i n v i s u a l a c u i t y . He a l s o noted that t h i s lack of c o r r e l a t i o n between age, c o l o r v i s i o n scores and v i s u a l a c u i t y could p o s s i b l y be e x p l a i n e d by the c r u d i t y of the t e s t i n g device ( i . e . , the PIC p l a t e s ) . Q u l e t t e (1955) t e s t e d 56 s u b j e c t s (28 young and 28 o l d s u b j e c t s ) on the I n t e r - S o c i e t y Color C o u n c i l Color A p t i t u d e Test (CAT). This t e s t r e q u i r e s d i s c r i m i n a t i o n of s m a l l d i f f e r e n c e s i n s a t u r a t i o n . She found that there was a 8 s i g n i f i c a n t d i f f e r e n c e between the performance of young (20 to 30 years) and ol d e r (75 to 85 years) s u b j e c t s ; the 2 age groups d i f f e r e d i n t h e i r a b i l i t y to d i s c r i m i n a t e f i n e degrees of s a t u r a t i o n . The young group showed 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 b e t t e r performance both o v e r a l l and a l s o for each of the 4 s p e c i f i c c o l o r groups. In 1957, G i l b e r t t e s t e d a large number of s u b j e c t s between 10 and 93 years using the same t e s t i n g procedure (CAT). She found that there was an improvement i n both the matching of i n d i v i d u a l c o l o r s and the t o t a l scores f o r c o l o r matching across the 2 groups of young s u b j e c t s (10 to 19 years and 20 to 29 y e a r s ) . Conversely, she found that there was a gradual d e c l i n e i n both with the ol d e r groups. A l l groups showed poorer d i s c r i m i n a t i o n f o r blue and green than f o r y e l l o w and red and t h i s weakness increased at a g r e a t e r r a t e with advancing age. Lakowski found a g e - r e l a t e d changes in c o l o r v i s i o n a b i l i t i e s using both pseudo-isochromatic p l a t e s and then the anomaloscope (Lakowski 1958; 1959; 1962). In the most comprehensive of these s t u d i e s , a l a r g e , random sample of observers from age 5 to 95 years were t e s t e d b i n o c u l a r l y under mesopic c o n d i t i o n s on an e a r l y model the P i c k f o r d anomaloscope. This instrument t e s t s a s u b j e c t ' s a b i l i t y to match w i t h i n metameric p a i r s . In g e n e r a l , he found that there i s a gradual d e c l i n e i n t h i s a b i l i t y with age but that the d i s c r i m i n a t i o n of some c o l o r p a i r s are more s t a b l e than o t h e r s . S p e c i f i c a l l y , red/green d i s c r i m i n a t i o n was found to be q u i t e s t a b l e u n t i l age 55 but changes i n y e l l o w - b l u e and v i o l e t / b l u e - g r e e n d i s c r i m i n a t i o n were ev i d e n t as e a r l y as 35 years of age. In o l d e r groups, Lakowski suggests that a new c l a s s of c o l o r v i s i o n d e f e c t i v e s becomes apparent; there i s an i n c r e a s e i n the number of observers i n the o l d e r groups who perform l i k e c o n g e n i t a l d e f e c t i v e s . He r e f e r s to t h i s group as pseudo-anomalous and includes i n i t the s u b j e c t s who have matching responses that l i e mid-way between those of normal observers and those of anomalous observers ( i . e . , those with c o n g e n i t a l c o l o r d e f e c t s ) (Lakowski 1962). The author suggests t h a t these changes i n c o l o r d i s c r i m i n a t i o n that he found i n the o l d e r observers could be a t l e a s t p a r t l y e x p l a i n e d by i n c r e a s e s i n o p t i c a l lens d e n s i t i e s . Color v i s i o n a b i l i t i e s can a l s o be examined with r e s p e c t to hue d i s c r i m i n a t i o n . Hue d i s c r i m i n a t i o n can be assessed with t e s t s such as the Farnsworth-Munsell 100-Hue t e s t . Using t h i s measure on normal t r i c h r o m a t s i t was found that hue d i s c r i m i n a t i o n d e t e r i o r a t e s with age ( V e r r i e s t , 1964; Wasilewski 1975; as c i t e d by Kalmus, 1987). Kalmus (1987) used the Lovibond Color V i s i o n Analyzer to study the c o n t r a s t c o l o r p e r c e p t i o n of s u b j e c t s of v a r i o u s ages. Subje c t s were t e s t e d b i n o c u l a r l y under i l l u m i n a n t C f o r both f o v e a l and p e r i p h e r a l v i s i o n . He found that there i s a l o s s with age f o r c o n t r a s t c o l o r p e r c e p t i o n e s p e c i a l l y when the c o l o r s t i m u l i are d e s a t u r a t e d ; the o l d e s t s u b j e c t s r e q u i r e d 3 times more l i g h t f o r the task than the young ones. 10 B. R e t i n a l Increment Threshold Studies The measurement of r e t i n a l increment t h r e s h o l d s i s an e f f e c t i v e and p r e c i s e method f o r a s s e s s i n g the e f f i c i e n c y of the v i s u a l system. I t does, however, i n v o l v e a complex, time-consuming and t e c h n i c a l l y d i f f i c u l t procedure. T h i s has r e s u l t e d i n i n c o n s i s t e n t methodological developments w i t h i n t h i s area of r e s e a r c h . V e r r i e s t was one of the e a r l i e r r e s e a r c h e r s to u t i l i z e increment s p e c t r a l s e n s i t i v i t i e s to examine the senescent v i s u a l system. A Goldmann s t a t i c perimeter was used to study the d i f f e r e n t i a l i n f l u e n c e of age and e c c e n t r i c i t y on mesopic s p e c t r a l s e n s i t i v i t i e s ( V e r r i e s t & I s r a e l , 1965). Subjects i n 3 age groups were t e s t e d with a white and some c o l o r e d s t i m u l i f o r both f o v e a l and p e r i p h e r a l s p e c t r a l increment t h r e s h o l d s . I t was found that i n the olde r s u b j e c t s , s p e c t r a l s e n s i t i v i t i e s decreased with the i n c r e a s i n g e c c e n t r i c i t y of the t e s t s t i m u l i . The macular and perimacular r e g i o n s , however, were an exception to t h i s ; the macular r e g i o n showed g r e a t e r l o s s e s than the perimacular zone of the r e t i n a . The a g e - r e l a t e d l o s s e s were most notable f o r blue s t i m u l i but the l o s s e s i n s e n s i t i v i t y were a l s o g r e a t e r f o r red s t i m u l i than f o r e i t h e r white or middle s p e c t r a l range s t i m u l i . The authors concluded that the combined e f f e c t s of changes i n the aging c r y s t a l l i n e l e n s ( i . e . , o p a c i f i c a t i o n and d i s c o l o r a t i o n of the lens) and of s e n i l e meiosis ( i . e . , l o s s i n p u p i l l a r y area) could e x p l a i n the l o s s i n s e n s i t i v i t y to the blue s t i m u l i . However, the decrease i n s e n s i t i v i t y f o r the red s t i m u l i c o u l d not be as e a s i l y e x p l a i n e d i n t h i s manner and i t was taken to i n d i c a t e a r o l e f o r r e t i n a l f a c t o r s i n the senescent v i s u a l system. T h i s g r e a t e r l o s s i n f o v e a l s e n s i t i v i t y f o r the red wavelengths r e l a t i v e to the middle range wavelengths was f u r t h e r supported by a study of f o v e a l f i e l d s u s i n g heterochromatic f l i c k e r photometry ( V e r r i e s t , 1970) . V e r r i e s t and Kandemir (1974) examined the r o l e that s e v e r a l v a r i a b l e s p l a y i n s p e c t r a l increment t h r e s h o l d s . The c o l o r ( i . e . , white and 9 wavelengths), s i z e and e c c e n t r i c i t y ( i . e . , at 5 r e t i n a l l o c a t i o n s a c r o s s the nasal h o r i z o n t a l meridian) of the t a r g e t s t i m u l i , and the i n t e n s i t y of the background luminance (which was presented i n an 11 degree annulus) were v a r i e d i n a p r e l i m i n a r y study conducted on 3 young s u b j e c t s . Based on these r e s u l t s , the parameters f o r a more extensive study were e s t a b l i s h e d . For the second study, the s u b j e c t s were d i v i d e d i n t o 2 age groups (young= 15 to 45 years and older= 60 to 75 y e a r s ) . The increment t h r e s h o l d s were determined on a modified Goldmann perimeter. The perimeter had been modified to produce a homogeneous a d a p t a t i o n f i e l d of 10.0 cd m~2 across the e n t i r e f i e l d ( i . e . , a high mesopic a d a p t a t i o n f i e l d ) . Increment t h r e s h o l d s were determined f o r 2 background luminances (3.15 and 10.0 cd m -^), 5 r e t i n a l l o c a t i o n s and the same white and 9 c o l o r e d t a r g e t s t i m u l i but only the l a r g e r t a r g e t s i z e (116') was used. In g e n e r a l , i t was 12 found that the old e r s u b j e c t s showed a reduced s e n s i t i v i t y under a l l c o n d i t i o n s when compared to the younger s u b j e c t s . T h i s l o s s i n s e n s i t i v i t y was greater for both s h o r t e r wavelength s t i m u l i and the lower l e v e l a d a p t a t i o n f i e l d . Both groups showed a decrease i n s e n s i t i v i t y f o r g r e a t e r e c c e n t r i c i t i e s . The r e s u l t s of the aforementioned study were extended i n 1977 by V e r r i e s t and U v i j l s with the i n c l u s i o n of a t h i r d , younger group of s u b j e c t s (10 to 15 years of age). S i m i l a r t e s t i n g parameters to those o u t l i n e d above were used except only the 10.0 cd m-^ background luminance was repeated here. The r e s u l t s were understandably s i m i l a r to those of the previous study; the o l d e s t group was l e s s s e n s i t i v e at a l l t e s t e d r e t i n a l l o c a t i o n s than the other 2 groups while the youngest group was more s e n s i t i v e than the middle group from 20 degrees e c c e n t r i c i t y and beyond except for the s h o r t e s t wavelength t a r g e t s t i m u l i ( A 451 nm). The olde r s u b j e c t s a l s o showed the g r e a t e s t s e n s i t i v i t y l o s s for the s h o r t e r wavelength t a r g e t s t i m u l i , an intermediate l o s s for the longer wavelength t a r g e t s t i m u l i and the l e a s t l o s s for the middle wavelength t a r g e t s t i m u l i . The t e s t i n g of two c o l o r increment t h r e s h o l d s i s a s p e c i f i c subset of r e t i n a l increment t h r e s h o l d assessments. This methodology can be used to t e s t each of the 3 cone systems independently; c o l o r e d t a r g e t l i g h t s are chosen to s t i m u l a t e a s i n g l e cone type and the a d a p t a t i o n f i e l d (background c o l o r ) i s chosen to s e l e c t i v e l y suppress the 13 other 2 cone mechanisms. In t h i s way, i t i s p o s s i b l e to examine the a g e - r e l a t e d l o s s e s i n a s i n g l e cone system. A recent study which employed t h i s methodology t e s t e d increment s p e c t r a l s e n s i t i v i t i e s at 76 l o c a t i o n s w i t h i n the c e n t r a l 30 degrees of the v i s u a l f i e l d under high photopic c o n d i t i o n s (200 cd m~2) (Johnson et a l , 1988). The experimental c o n d i t i o n s were chosen i n an attempt to both i s o l a t e the s h o r t - w a v e l e n g t h - s e n s i t i v e (SWS) cone pathways and to help minimize the e f f e c t s of ocular media a b s o r p t i o n and s e n i l e m e i o s i s . That i s , a l a r g e blue t a r g e t (1.6 degrees) was presented on a high luminance, y e l l o w background (200 cd m - 2 ) . A l e a s t squares l i n e a r r e g r e s s i o n of SWS cone pathway s e n s i t i v i t y and age i n d i c a t e d t h at there was approximately a 0.15 l o g u n i t l o s s i n s e n s i t i v i t y per decade. The l i n e a r f u n c t i o n , however, was not constant across the age continuum; there was a gradual s e n s i t i v i t y l o s s i n SWS cone pathways before age 50 years and a more a c c e l e r a t e d l o s s a f t e r that p o i n t . A s i m i l a r approach was taken by Haegerstrom-Portnoy et a l (1989). They used the c o l o r increment technique to independently examine a g e - r e l a t e d changes i n the SWS and l o n g - w a v e l e n g t h - s e n s i t i v e (LWS) cone pathways i n 61 s u b j e c t s (a young c o n t r o l group and 3 groups from 50 to over 70 y e a r s ) . To i s o l a t e the SWS cone pathway, two blue s t i m u l i ( A 440 nm and A 480 nm) were presented on a y e l l o w background (3.95 l o g t r o l a n d s i n a 10 degree annulus). Conversely, to i s o l a t e the LWS cone pathways, a yellow-green stimulus ( 570 nm) was presented on a blue background (3.47 l o g t r o l a n d s i n a 10 degree a n n u l u s ) . They found no l o s s e s i n the LWS cone pathways i n any age group but d i d f i n d a 0.4-0.5 l o g u n i t l o s s i n the SWS cone pathways of the s u b j e c t s i n the o l d e r age group; SWS cone pathway s e n s i t i v i t y f o r the o l d e r observers was more v a r i a b l e and on average lower than f o r the younger observers (Haegerstrom-Portnoy et a l 1989). C. S t u d i e s on the r o l e of p r e r e c e p t o r a l f a c t o r s i n age- r e l a t e d c o l o r v i s i o n changes I t has been w e l l e s t a b l i s h e d t h a t there are s u b s t a n t i a l a g e - r e l a t e d changes i n the o p t i c a l d e n s i t y of the human c r y s t a l l i n e lens ( f o r example, Said & Weale, 1959). I t i s assumed by many r e s e a r c h e r s that these changes are the main f a c t o r s which cause the normal a g e - r e l a t e d d i f f e r e n c e s i n c o l o r d i s c r i m i n a t i o n . Several l i n e s of r e s e a r c h have been followed i n an attempt to e s t a b l i s h how much of a r o l e p r e r e c e p t o r a l f a c t o r s p l a y i n the observed f u n c t i o n a l l o s s e s i n c o l o r v i s i o n . (1) The study of p h y s i o l o g i c a l changes i n the le n s . Said and Weale (1959) e s t a b l i s h e d the o p t i c a l d e n s i t i e s ( i . e . , a b sorbing p r o p e r t i e s ) of the l i v i n g ( i . e . , i n vivo) human c r y s t a l l i n e l e n s at s e v e r a l ages u s i n g an o b j e c t i v e assessment procedure. O p t i c a l d e n s i t y i s i n v e r s e l y r e l a t e d to s p e c t r a l t r a n s m i s s i v i t y . S p e c t r a l t r a n s m i s s i v i t y i s a measure of the s e l e c t i v e f i l t e r i n g p r o p e r t i e s of a substance (I.e., a measure of what wavelength energy Is allowed to pass through a subst a n c e ) . In t h i s study, they found that the s p e c t r a l t r a n s m l s s i v l t y was constant f o r s u b j e c t s up to 20 years of age but that i t decreased l i n e a r l y up to age 63 years of age. (2) The study of aphakic observers. To i s o l a t e the r o l e of l e n s changes i n a g e - r e l a t e d changes i n c o l o r v i s i o n f u n c t i o n , attempts have been made to remove the e f f e c t s of the lens d u r i n g t e s t i n g . An e a r l y study i n t h i s area te s t e d s u b j e c t s with one aphakic and one phakic eye and a l s o those with b i n o c u l a r aphakia on the P i c k f o r d anomaloscope (Lakowski, 1962). With the f i r s t group, i t was found that the aphakic eye had much b e t t e r wavelength d i s c r i m i n a t i o n than the co r r e s p o n d i n g phakic eye. A l s o , the phakic eyes showed d i s c r i m i n a t i o n a b i l i t i e s that were e q u i v a l e n t to those of aged matched normal phakic s u b j e c t s . The second group was s u b d i v i d e d i n t o four groups a c c o r d i n g to the l e v e l of pigmentation i n t h e i r macular r e g i o n . Three general r e s u l t s were found. F i r s t l y , i n the younger subgroup of aphakics, there was no i n d i c a t i o n of improvement in c o l o r matching a b i l i t y with r e s p e c t to age-matched phakic s u b j e c t s . Secondly, i n the older aphakic s u b j e c t s with normal macular pigmentation, there was an o v e r a l l improvement i n t h e i r c o l o r matching a b i l i t i e s as compared to t h e i r age-matched c o n t r o l s but the improvement r a r e l y r eturned them to the f i n e d i s c r i m i n a t i o n a b i l i t i e s of normal 20 year o l d s . T h i r d l y , i n the s u b j e c t s with n o t i c e a b l e p a t h o l o g i c a l pigment e p i t h e l i a l pigmentation ( i . e . , c h o r i o d d i s e a s e ) , t h e i r c o l o r d i s c r i m i n a t i o n was found to be even worse that i n the general aged p o p u l a t i o n . The author concluded that although s e n i l e lens changes appear to be p a r t i a l l y r e s p o n s i b l e f o r the observed decrease i n c o l o r d i s c r i m i n a t i o n a b i l i t i e s i n the general aged p o p u l a t i o n , the removal of the lens seldom r e t u r n s a b i l i t i e s to the l e v e l of the young observers. Aphakics i n two age groups were t e s t e d using heterochromatic f l i c k e r photometry to e s t a b l i s h r e t i n a l s p e c t r a l f o v e a l s e n s i t i v i t i e s ( V e r r i e s t , 1972). It was found t h a t i n the absence of the c r y s t a l l i n e lens ( i . e . , i n aphakic eyes), the r e t i n a l s p e c t r a l luminous e f f i c i e n c y d i d n ' t s i g n i f i c a n t l y change with advancing age; there were 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 means for the 2 age groups of aphakic s u b j e c t s . When the s p e c t r a l s e n s i t i v i t i e s of age-matched phakic s u b j e c t s were compared to those of the aphakic s u b j e c t s , i t was found t h a t there was a much g r e a t e r l o s s i n the short wavelength range ( A 441 to A 514 nm) of the spectrum for the phakic eyes. In a d d i t i o n , the phakic eyes a l s o showed more l o s s f o r the extreme long wavelength range ( A 691 nm and beyond) but they showed smaller l o s s e s i n the range from A 595 to A 658 nm when compared to the aphakic ones. From these f i n d i n g s , i t was concluded t h a t lens changes are, at l e a s t , p a r t i a l l y r e s p o n s i b l e f o r the observed a g e - r e l a t e d l o s s e s i n s p e c t r a l s e n s i t i v i t y . A l s o , a mean s p e c t r a l curve of the r e l a t i v e o p t i c a l d e n s i t y of the c r y s t a l l i n e lens was c a l c u l a t e d from the r e s u l t s ( I . e . , the d i f f e r e n c e between the mean s p e c t r a l curves of r e l a t i v e luminous e f f i c i e n c y f o r aphakics vers e s phakics i n the 2 d i f f e r e n t age groups). These r e s e a r c h e r s concluded from these f i n d i n g s that the longer wavelength energy i s absorbed to a g r e a t e r extent by the c r y s t a l l i n e lens than are the middle range wavelengths. Furthermore, i t was concluded t h a t R a y l e i g h s c a t t e r i n g , t h e r e f o r e , not be the s o l e f a c t o r which a f f e c t s l i g h t t r a n s m i s s i o n by the l e n s . (3) Studies which attempt to simulate a g e - r e l a t e d lens changes. In h i s study of c o l o r matching a b i l i t i e s w i t h i n an age continuum, Lakowski suggested t h a t at l e a s t some of the t y p i c a l changes i n c o l o r v i s i o n a b i l i t i e s t h a t he found i n the o l d e r s u b j e c t s could be e x p l a i n e d by i n c r e a s e s i n the d e n s i t y of the o p t i c a l l e n s . Lakowski (1962) used g e l a t i n y e l l o w f i l t e r s which c l o s e l y resemble the d e n s i t y c h a r a c t e r i s t i c s of the lens and the lens and macula combined (as o u t l i n e d by Said and Weale (1959) and Wald (1945) r e s p e c t i v e l y ) to simulate a g e - r e l a t e d l e n s changes. He t e s t e d young observers on the P i c k f o r d anomaloscope with these f i l t e r s i nterposed i n f r o n t of t h e i r eyes. He found t h a t , f o r the m a j o r i t y of normal s u b j e c t s the o p t i c a l lens d e n s i t i e s quoted by Said and Weale were not s u f f i c i e n t to reproduce the changes i n c o l o r matching t h a t had been found i n the aged s u b j e c t s , e s p e c i a l l y a t the sh o r t wavelength end of the spectrum; normal o p t i c a l changes i n only the lens are not s u f f i c i e n t to account f o r the observed a g e - r e l a t e d changes i n c o l o r matching a b i l i t y . Conversely, he found t h a t the combined o p t i c a l d e n s i t i e s of the lens and the macula could account f o r a s u b s t a n t i a l p a r t of these age-r e l a t e d changes at the v i o l e t end of the spectrum. I t i s i n t e r e s t i n g to note t h a t Lakowski found t h a t the y e l l o w f i l t e r s had a g r e a t e r impact on young s u b j e c t s who had o r i g i n a l l y had l e s s than p e r f e c t c o l o r d i s c r i m i n a t i o n . He suggested that the pseudo-anomalous s u b j e c t s that he found i n the o l d e r group may have belonged to t h i s group of observers when they were younger. (4) S t u d i e s which attempt to f a c t o r out the e f f e c t s of a g e - r e l a t e d lens changes. In t h e i r r e c e n t study on age-r e l a t e d changes i n s h o r t - w a v e l e n g t h - s e n s i t i v e (SWS) cone pathways, Johnson et a l (1988) attempted to f a c t o r out the r o l e of changes i n the absorbing p r o p e r t i e s of the aging o c u l a r media. The dark-adapted s c o t o p i c t h r e s h o l d s were e s t a b l i s h e d f o r each eye (at 15 degrees both n a s a l l y and temporally) on the TUbinger Perimeter f o r both shor t ( A 450 nm) and long ( A 656 nm) s t i m u l i and these t h r e s h o l d s were used as the p r e - r e t i n a l a b s o r p t i o n c o r r e c t i o n f a c t o r . I t was found that the p r e - r e t i n a l a b s o r p t i o n of s h o r t -wavelength energy i n c r e a s e d g r a d u a l l y up to age 60 years and a f t e r that p o i n t , i t i n c r e a s e d more r a p i d l y . I t was a l s o e s t a b l i s h e d t h a t there were r e l a t i v e l y l a r g e i n d i v i d u a l d i f f e r e n c e s i n these p r e - r e t i n a l a b s o r p t i o n f a c t o r s . This was e s p e c i a l l y t r u e f o r the older group ( i . e . , s u b j e c t s over 60 years of age). In the f i r s t part of t h i s study, as d e s c r i b e d e a r l i e r , SWS cone pathway increment t h r e s h o l d s e n s i t i v i t i e s were e s t a b l i s h e d for a blue t a r g e t on a high luminance, y e l l o w background. The r e s u l t s i n d i c a t e d that there was a 0.15 l o g u n i t l o s s i n s e n s i t i v i t y per decade. The obtained p r e r e t i n a l c o r r e c t i o n f a c t o r s were then a p p l i e d to t h i s data, and i t was found that the SWS l o s s was reduced to approximately 0.09 l o g u n i t per decade. From t h i s , i t was assumed t h a t 30 to 40 per cent of the a g e - r e l a t e d l o s s i n SWS must be due to the increase i n p r e - r e t i n a l ocular media a b s o r p t i o n with age. I t was found t h a t there was an o v e r a l l a g e - r e l a t e d "loss i n s e n s i t i v i t y throughout the c e n t r a l v i s u a l f i e l d . In a d d i t i o n , t h i s l o s s i n creased with i n c r e a s i n g e c c e n t r i c i t y e s p e c i a l l y f o r the s u p e r i o r and n a s a l v i s u a l f i e l d s . I t was a l s o noted t h a t the between s u b j e c t v a r i a n c e was g r e a t e r a f t e r the p r e - r e t i n a l c o r r e c t i o n f a c t o r was a p p l i e d . T h i s probably i s p a r t l y a r e f l e c t i o n of the l a r g e i n d i v i d u a l d i f f e r e n c e s found i n the p r e - r e t i n a l a b s o r p t i o n f a c t o r s . The authors noted that the eyes with the l a r g e r p r e - r e t i n a l a b s o r p t i o n c o r r e c t i o n f a c t o r s tended to have the greater SWS cone pathway s e n s i t i v i t i e s . The authors concluded that the a b s o r p t i o n f a c t o r and SWS cone pathway s e n s i t i v i t i e s are not independent; higher s e n s i t i v i t i e s were a s s o c i a t e d with l a r g e r p r e - r e t i n a l a b s o r p t i o n f a c t o r s . T h i s tendency was a l s o g r e a t e s t i n the eyes where the g r e a t e r p r e - r e t i n a l a b s o r p t i o n had been probably been present f o r a longer p e r i o d of time ( i . e . , the older s u b j e c t s ) . The authors p r o f f e r e d a theory to e x p l a i n t h i s r e l a t i o n s h i p ; the senescent y e l l o w i n g of the c r y s t a l l i n e lens provides some p r o t e c t i o n to the SWS cone pathways from l i g h t - i n d u c e d damage. F u r t h e r , they suggest t h a t t h i s p r o t e c t i o n probably does not o r i g i n a t e c e n t r a l l y because there were i n t e r o c u l a r d i f f e r e n c e s i n p r e - r e t i n a l a b s o r p t i o n and SWS cone pathway s e n s i t i v i t i e s i n the olde r s u b j e c t s . In t h e i r recent study using two c o l o r increment t h r e s h o l d s to examine a g e - r e l a t e d changes i n both SWS and long- w a v e l e n g t h - s e n s i t i v e (LWS) cone pathway s e n s i t i v i t i e s , Haegerstrom-Portnoy and her c o l l e a g u e s (1989) addressed the issue of how much of a r o l e p r e - r e t i n a l f a c t o r s play i n the observed f u n c t i o n a l l o s s e s i n c o l o r v i s i o n . Subjects were t e s t e d s e p a r a t e l y f o r both SWS and LWS cone pathway s e n s i t i v i t i e s by using s p e c i f i c s t i m u l u s wavelengths and adap t i n g f i e l d s as des c r i b e d e a r l i e r . Then an attempt was made to independently assess the t r a n s m i s s i o n of the oc u l a r media f o r each s u b j e c t . Subjects were t e s t e d for t h e i r f l i c k e r (25 hz) t h r e s h o l d s e n s i t i v i t y to s e v e r a l wavelengths on a white background (3.12 l o g t r o l a n d s ) . This procedure i n d i c a t e d t h a t there are d i f f e r e n c e s i n the t r a n s m i s s i o n of the o c u l a r media across ages and th a t t h i s d i f f e r e n c e i s g r e a t e s t f o r the sh o r t e r wavelengths. A l s o , i t was found t h a t there was a greater v a r i a b i l i t y i n t r a n s m i s s i o n values among the o l d e r observers. In a d d i t i o n , an ocular media a b s o r p t i o n c o r r e c t i o n f a c t o r was c a l c u l a t e d . The f l i c k e r t h r e s h o l d s e n s i t i v i t y f o r the o l d e r observers at the 480 nm 21 s t i m u l u s was compared ag a i n s t the r e s u l t s f o r a young observer without ocular o p a c i t i e s ( i . e . , a template). The d i f f e r e n c e between the 2 r e s u l t s was used as the a b s o r p t i o n c o r r e c t i o n f a c t o r . When the o r i g i n a l c o l o r increment t h r e s h o l d data was reevaluated u s i n g t h i s a b s o r p t i o n c o r r e c t i o n f a c t o r , the SWS cone pathway s e n s i t i v i t y l o s s was reduced to 0.2 log u n i t s (a r e d u c t i o n of approximately 50%). The a b s o r p t i o n f a c t o r d i d account f o r s u b s t a n t i a l p a r t of the l o s s i n SWS cone pathway but there s t i l l remained a s m a l l but s i g n i f i c a n t l o s s i n these pathways. The c o r r e c t i o n f a c t o r , however, d i d not reduce the v a r i a b i l i t y of the measures for the older o b s e r v e r s . The authors concluded that some s e n i l e n e u r a l l o s s would probably account f o r t h i s d i f f e r e n c e . Of course, n e i t h e r of these s t u d i e s addressed the f u l l range of s p e c t r a l s e n s i t i v i t i e s s i n c e both were completed with s e l e c t i v e a d a p t a t i o n f i e l d s ( i . e . , y e l l o w background). In a d d i t i o n , because again only a s m a l l a d a p t a t i o n f i e l d was used, i t i s q u e s t i o n a b l e that photopic a d a p t a t i o n was a c t u a l l y a c h i e v e d . I I . T h e o r e t i c a l P e r s p e c t i v e s on R e t i n a l Increment Threshold Measurements A p s y c h o p h y s i c a l model of v i s u a l d e t e c t i o n has been e s t a b l i s h e d which i n d i c a t e s that the v i s u a l system i s comprised of 2 p a r a l l e l , independent channels; an achromatic (luminance d e t e c t i n g ) system and a chromatic (hue determining) system. T h i s , however, i s a r e l a t i v e l y r ecent development i n t h i s area of r e s e a r c h . The study of and t h e o r e t i c a l framework for s p e c t r a l s e n s i t i v i t y f u n c t i o n s probably o r i g i n a t e d with S t i l e s ' two c o l o r t h r e s h o l d technique. His model d e s c r i b e d the v i s u a l system i n terms of s e v e r a l p a r a l l e l and independent II mechanisms. These proposed s p e c t r a l s e n s i t i v i t y f u n c t i o n s corresponded to the 3 Young-Helmholtz mechanisms. His model s t a t e s that any t a r g e t s t i m u l u s that i s above the t h r e s h o l d f o r any of these mechanisms w i l l be detected. Both cones and rods were i m p l i c a t e d i n t h i s model with 1 mechanism a t t r i b u t e d to the rods and 1 or more to each of the 3 cone types. I t was necessary f o r S t i l e s to propose 7 II mechanisms to account f o r h i s experimental f i n d i n g s . This presented a concern about the model s i n c e i t i s r o u t i n e l y accepted that there are o n l y 3 cone types and that these cones e x h i b i t c h a r a c t e r i s t i c a b s o r p t i o n s p e c t r a . The s p e c t r a l s e n s i t i v i t y curves of S t i l e s ' mechanisms are i n g e n e r a l broader than the cone a b s o r p t i o n s p e c t r a and t h e i r peaks are sometimes s h i f t e d . Researchers who have repeated S t i l e s ' experiments on t r a n s i e n t a d a p t a t i o n f i e l d s found s p e c t r a l s e n s i t i v i t y curves that were narrower and more r e p r e s e n t a t i v e of the cone a b s o r p t i o n s p e c t r a (Boynton, 1964; King-Smith & Webb, 1974). This d i f f e r e n c e may be a r e s u l t of the s u s t a i n e d background o r i g i n a l l y used by S t i l e s . I t has s i n c e been proposed that 2 mechanisms could be used to d e s c r i b e v i s u a l d e t e c t i o n with respect to s p e c t r a l s e n s i t i v i t y ( i . e . , r e t i n a l t h r e s h o l d s ) . King-Smith and h i s c o l l e a g u e s were the f i r s t to propose that these 2 systems could be d e s c r i b e d i n terms of c o l o r opponent and luminance s i g n a l s . The f i n d i n g s of t h e i r r e s e a r c h favor the Hering opponent process c o l o r v i s i o n theory. I t i s p r o f f e r e d that these 2 systems are p a r a l l e l and independent (although exceptions are noted, see f o r example, C o l e t t a and Adams, 1986). As evidence of t h i s , many re s e a r c h e r s p o i n t to the d i s t i n c t l y d i f f e r e n t s p a t i a l and temporal c h a r a c t e r i s t i c s of the 2 systems. The temporal c h a r a c t e r i s t i c s of these 2 systems was f i r s t demonstrated by DeLange i n 1958. The achromatic system i s more s e n s i t i v e to s m a l l , s h o r t - d u r a t i o n t e s t f l a s h e s while the chromatic system i s more s e n s i t i v e to l a r g e r , l o n g - d u r a t i o n t e s t f l a s h e s . That i s , the achromatic system shows s h o r t e r temporal and poorer s p a t i a l i n t e g r a t i v e p r o p e r t i e s than the chromatic system. In a d d i t i o n , the achromatic system i s a l s o separated from the chromatic system i f the t e s t - f l a s h i s presented on a high luminance white background ( i . e . , the achromatic system w i l l be s e l e c t i v e l y suppressed under these c o n d i t i o n s ) . The r e s u l t a n t f u n c t i o n s of these two systems are a l s o d i s t i n c t l y d i f f e r e n t from one another. The achromatic s p e c t r a l s e n s i t i v i t y f u n c t i o n i s a broad i n v e r t e d curve with a s i n g l e maxima at approximately A 555 nm. I t i s q u i t e s i m i l a r to the photopic VA curve. Conversely, the chromatic s p e c t r a l s e n s i t i v i t y f u n c t i o n has 3 peaks which are roughly r e p r e s e n t the blue, green and red cone systems ( f o r example, a t A 445 nm, between A 530 and A 540 nm and at A 610 nm, S p e r l i n g and Harwerth, 1971; at A 440, A 530 and A 600 nm King-Smith & Carden, 1975). These c h a r a c t e r i s t i c s are now commonly used i n order to independently t e s t these two systems; t h i s approach w i l l a l s o be used h e r e i n . I I I . M e t hodological C o n s i d e r a t i o n s f o r the Present Study (1) Photopic Adaptation F i e l d The most fundamental v a r i a b l e i n v i s i o n i s the l e v e l of the surrounding i l l u m i n a t i o n which determines the l e v e l of v i s u a l a d a p t a t i o n and thus the a p p r o p r i a t e v i s u a l p r o c e s s . V i s i o n i s s a i d to be photopic i f the eye i s adapted to d a y l i g h t , mesopic i f i t i s adapted to t w i l i g h t , and s c o t o p i c when adapted to minimal amounts of l i g h t (Lakowski, 1969). There have been no s t u d i e s which have examined increment s p e c t r a l s e n s i t i v i t i e s under t o t a l l y photopic c o n d i t i o n s ( i . e . , with complete rod s a t u r a t i o n ) . Most of the s t u d i e s are performed with photopic a d a p t a t i o n background l e v e l s presented only w i t h i n a c e n t r a l annulus ( u s u a l l y of approximately 10 degrees). T h i s a d a p t a t i o n method presents some concerns. F i r s t l y , i t i s only p o s s i b l e to t e s t f o v e a l t h r e s h o l d s using an annulus p r e s e n t a t i o n of the a d a p t a t i o n f i e l d . Secondly, and i n a d d i t i o n , i t i s uncle a r that such a l i m i t e d a d a p t a t i o n f i e l d can serve to adapt the v i s u a l system to photopic l e v e l s p r o p e r l y . The s t u d i e s t h a t do use an a d a p t a t i o n f i e l d which covers the complete t e s t i n g s u r f a c e tend to use lower a d a p t a t i o n l e v e l s ( f o r example, V e r r i e s t 1974; V e r r i e s t & U V i j l s , 1977). I t Is more l i k e l y t h a t these a d a p t a t i o n l e v e l s are a c t u a l l y mesopic r a t h e r than t r u l y photopic. At mesopic l e v e l s of a d a p t a t i o n , there i s s t i l l an i n t e r a c t i o n between the cone and rod r e c e p t o r s . T h i s i n t e r a c t i o n can be e l i m i n a t e d by using high photopic a d a p t a t i o n f i e l d s which s a t u r a t e the rod f u n c t i o n and a l l o w the cones to be assessed i n i s o l a t i o n . The i s s u e of a p p r o p r i a t e a d a p t a t i o n l e v e l s becomes more c r i t i c a l when the s u b j e c t s are e l d e r l y . That i s , given what i s know about the a g e - r e l a t e d p h y s i o l o g i c a l changes i n the v i s u a l system ( i . e . , i n c r e a s e s i n p r e r e c e p t o r a l a b s o r p t i o n ) , i t can be expected that the amount of ambient l i g h t necessary to achieve photopic a d a p t a t i o n l e v e l s w i l l only i n c r e a s e with advancing age. (2) Target S t i m u l i The v i s i b l e spectrum r e f e r s to the range of el e c t r o m a g n e t i c r a d i a t i o n to which the human v i s u a l system i s v i s u a l l y r e s p o n s i v e . I t ranges from A 400 to A 700 nanometers (nm). Most s t u d i e s of s p e c t r a l s e n s i t i v i t i e s and age use a l i m i t e d number of wavelengths as t a r g e t s t i m u l i . The present study w i l l include a more complete wavelength d i s t r i b u t i o n than i s normally used; 21 wavelengths ranging from A 420 nm to A 651 nm w i l l be used f o r the achromatic s p e c t r a l s e n s i t i v i t i e s and 16 of these same wavelengths w i l l be used f o r the chromatic s p e c t r a l s e n s i t i v i t i e s . T h i s w i l l a l l o w f o r a more p r e c i s e assessment of a g e - r e l a t e d changes i n s e n s i t i v i t y to s p e c i f i c ranges of the s p e c t r a l d i s t r i b u t i o n (3) V i s u a l A c u i t y R e f r a c t i v e e r r o r s have been e s t a b l i s h e d to i n c r e a s e r e t i n a l t h r e s h o l d s f o r the c e n t r a l 25 degrees of the v i s u a l f i e l d (Aulhorn & Harms, 1972). The best s o l u t i o n to t h i s problem i s to t e s t o n l y emmetropic observers. T h i s , however, i s not f e a s i b l e with an aged p o p u l a t i o n s i n c e i t i s u n l i k e l y t h a t many people have emmetropic v i s i o n i n t o t h e i r l a t e r y e a r s . In order to help c o n t r o l f o r the e f f e c t of v i s u a l a c u i t y on these t e s t s , only s u b j e c t s with uncorrected or c o r r e c t e d v i s i o n of at l e a s t 20/40 w i l l be used. (4) P u p i l s i z e P u p i l s i z e i n f l u e n c e s r e t i n a l increment t h r e s h o l d s by l i m i t i n g the amount of l i g h t t h a t can reach the r e t i n a (Sloan, 1940). I t i s p o s s i b l e to c o n t r o l the p u p i l s i z e d u r i n g t e s t i n g procedures with the use of e i t h e r an a r t i f i c i a l p u p i l or pharmaceuticals. Neither of these would be a p p r o p r i a t e w i t h i n the context of the present study. The use of a r t i f i c i a l p u p i l s i s p r o h i b i t i v e l y demanding and d i f f i c u l t f o r the s u b j e c t and s i n c e many of the s u b j e c t s who w i l l p a r t i c i p a t e i n t h i s study w i l l be e l d e r l y , t h i s i s not a v i a b l e o p t i o n . The use of pharmaceuticals would a l s o not be a p p r o p r i a t e s i n c e t h i s t e s t i n g w i l l not be undertaken with the s u p e r v i s i o n of medical personnel (for a more complete d i s c u s s i o n of these i s s u e s , r e f e r to Sloan, 1940; Dunn, 1979). E l d e r l y observers are expected to have a reduced p u p i l l a r y area ( i . e . , s e n i l e meiosis) with respect to the younger subjects. Subject pupil diameter is assessed during testing and is included in the calculations of the r e t i n a l increment thresholds. This should help account for individual differences in pupil diameter. In addition, the highly photopic adaptation f i e l d should help to ensure that subjects w i l l have a pupil size close to the natural pupil size of 3 mm. IV. Proposal It was apparent from the l i t e r a t u r e that l i t t l e information has been presented on r e t i n a l increment thresholds obtained under the proposed conditions ( f u l l y photopic, extensive range of colored targets, completed within a normal aging population). In addition, there have been no studies which have included the assessment of both achromatic and chromatic spectral s e n s i t i v i t i e s under the same testing conditions. Objectives The present project w i l l be separated into 2 studies. EXPERIMENT I The f i r s t objective of th i s research was to investigate the influence of the normal ( i . e . , in the absence of pathological conditions) aging process on t r u l y photopic achromatic and chromatic increment r e t i n a l thresholds for an extensive range of colored targets. The second objective was to establish the range the normal variations for these 28 r e t i n a l t h r e s h o l d s f o r s e v e r a l age group w i t h i n a normal p o p u l a t i o n . The s u b j e c t s had normal t r i c h r o m a t i c c o l o r v i s i o n , uncorrected or c o r r e c t e d v i s u a l a c u i t y of not l e s s than 20/40 and no p a t h o l o g i c a l c o n d i t i o n s ( i . e . , known to a f f e c t v i s u a l performance). The su b j e c t s were arranged i n t o seven age groups, ranging from 13 to 82 years of age, with between 5 and 10 s u b j e c t s i n each group. An attempt was made to ob t a i n equal numbers of females and males i n each age group. EXPERIMENT II The o b j e c t i v e of t h i s study was to develop a p r e l i m i n a r y model of the r o l e of p r e r e c e p t o r a l f a c t o r s i n the a g e - r e l a t e d changes i n r e t i n a l increment t h r e s h o l d s using the same p r o t o c o l as i n experiment I. An attempt was made to simulate the combined l e n t i c u l a r and macular changes a s s o c i a t e d with age a t three s p e c i f i c ages. Subjects were t e s t e d for achromatic and chromatic r e t i n a l t h r e s h o l d s under normal c o n d i t i o n s and then under 5 experimental c o n d i t i o n s . These experimental c o n d i t i o n s involved the i n t e r p o s i t i o n of g e l a t i n f i l t e r s which simulate the o p t i c a l p r o p e r t i e s of the aging lens and macula at 4 d i f f e r e n t ages ( d e n s i t y values from work by Said & Weale, 1959 and Wald, 1945). Subjects were r e t e s t e d f o r achromatic and chromatic s p e c t r a l s e n s i t i v i t i e s under each of these f i l t e r c o n d i t i o n s . each f i l t e r c o n d i t i o n was run i n con j u n c t i o n with the c o n t r o l ( i . e . , no f i l t e r ) c o n d i t i o n . Each f i l t e r c o n d i t i o n , t h e r e f o r e , was compared to i t s own b a s e l i n e c o n d i t i o n . The s u b j e c t s were three young, h e a l t h y observers who were w i l l i n g to be i n v o l v e d i n the repeated t e s t i n g that was necessary f o r t h i s study. Hypotheses The f o l l o w i n g a p r i o r i hypotheses were advanced with r e s p e c t to the trends noted i n the l i t e r a t u r e on r e t i n a l increment t h r e s h o l d s and age: EXPERIMENT I 1) Higher t h r e s h o l d s ( i . e . , reduced s e n s i t i v i t i e s ) are expected for both the achromatic and chromatic s p e c t r a l s e n s i t i v i t i e s i n the short-wavelength range of the spectrum f o r the older ( i . e . , over 60 years of age) s u b j e c t s with r e s p e c t to the younger ( i . e . , under 30 year s ) s u b j e c t s . 2) S l i g h t l y higher t h r e s h o l d s ( i . e . , reduced s e n s i t i v i t i e s ) are expected f o r the achromatic and chromatic f u n c t i o n i n the long-wavelength range of the spectrum f o r the old e r s u b j e c t s with r e s p e c t to the younger s u b j e c t s . 3) A sma l l e f f e c t i s expected f o r both the achromatic and chromatic s p e c t r a l s e n s i t i v i t i e s i n the middle-wavelength range of the spectrum f o r the o l d e r s u b j e c t s with r e s p e c t to the younger s u b j e c t s . I t i s expected t h a t these a n t i c i p a t e d l o s s e s w i l l appear g r a d u a l l y a c r o s s the age continuum but i t i s not c l e a r at what p o i n t we should expect these d i f f e r e n c e s to become s i g n i f i c a n t . EXPERIMENT II 1) Higher t h r e s h o l d s ( i . e . , reduced s e n s i t i v i t i e s ) are expected f o r the achromatic f u n c t i o n i n the short-wavelength range of the spectrum for the young s u b j e c t s when the 4 g e l a t i n f i l t e r s ( i . e . , over 63 years s i m u l a t i o n ) are in t e r p o s e d i n t h e i r v i s u a l pathway. Intermediate l o s s e s are expected i n the achromatic f u n c t i o n with the l e s s e r f i l t e r arrangements ( i . e . , lower age s i m u l a t i o n s ) . 2) Higher t h r e s h o l d s ( i . e . , reduced s e n s i t i v i t i e s ) are expected f o r the chromatic f u n c t i o n i n the short-wavelength range of the spectrum for the young" s u b j e c t s when the 4 g e l a t i n f i l t e r s are interposed i n t h e i r v i s u a l pathway with r e s p e c t to the no f i l t e r c o n d i t i o n . Intermediate l o s s e s are expected i n the chromatic f u n c t i o n with the other f i l t e r arrangements. 3) L i t t l e or no e f f e c t i s expected f o r e i t h e r the achromatic and chromatic r e t i n a l increment thresholds i n e i t h e r the middle-wavelength or long-wavelength ranges of the spectrum with r e s p e c t to the no f i l t e r c o n d i t i o n . Method Apparatus Per imeter Chromatic and achromatic f o v e a l r e t i n a l t h r e sholds were assessed u s i n g a modified Goldmann P r o j e c t i o n Perimeter, the B r i t i s h Columbia U n i v e r s a l Photometer (BCUP) (Lakowski et a l , 1977). The perimeter c o n s i s t s of a hemispheric bowl (diameter 60.6 cm) i n t o which a background source and a t a r g e t source are p r o j e c t e d . Both the background and t a r g e t luminances are provided by xenon a r c lamps which have s p e c t r a l d i s t r i b u t i o n s t h a t approximate the CIE I l l u m i n a n t C (Figure 1, Wyszecki & S t i l e s , 1967). There are d i f f u s i o n b a f f l e s mounted acr o s s the top and bottom f r o n t s u r f a c e s of the bowl which serve to reduce l i g h t l o s s from the bowl and to i n c r e a s e the d i f f u s i o n of the background luminance (they i n c r e a s e the background luminance by approximately 70 per c e n t ) . The e n t i r e inner t e s t i n g s u r f a c e of the perimeter i s coated with a smooth, homogeneous r e f l e c t i v e s u r f a c e , Eastman Kodak White R e f l e c t i v e P a i n t . This s u r f a c e provides a 98 per cent r e f l e c t a n c e across the e n t i r e v i s i b l e spectrum which helps to preserve the high luminance, i l l u m i n a n t C p r o p e r t i e s of the source. The BCUP i s equipped with s e v e r a l f e a t u r e s which are important f o r m a i n t a i n i n g the head and eye p o s i t i o n of the s u b j e c t . F i r s t l y , there i s a c h i n r e s t at the f r o n t of the bowl which can be moved p a r a l l e l to the t e s t i n g s u r f a c e (both h o r i z o n t a l l y and v e r t i c a l l y ) to a l i g n the s u b j e c t s eye i n the center of the f i e l d . I t a l s o serves to maintain the s u b j e c t s ' eye at 30 cm from the t e s t i n g s u r f a c e . Secondly, there i s a t e l e s c o p e mounted i n t o the bowl which allows the operator to monitor the s u b j e c t ' s eye throughout the t e s t i n g procedure. The t e l e s c o p e i s graduated in m i l l i m e t e r s for the measurement of the s u b j e c t ' s p u p i l . F i n a l l y , there i s a d e v i c e t h a t p r o j e c t s a f o u r - s p o t f i x a t i o n p a t t e r n onto the 32 C I E I l l u m l n a n t C t \ jo yo •0 , to t>o « e w iU i« t;0 eu f'l9 <i ^ ^ ,;e Wavelength F i g u r e 1. R e l a t i v e s p e c t r a l energy d i s t r i b u t i o n of C.I.E. I l l u m l n a n t C and the Xenon-arc (from Wyszecki and S t i l e s , 1967; Dunn, 1979). bowl which a i d s with f o v e a l f i x a t i o n . The placement of t h i s p a t t e r n can be ad j u s t e d and i t was set at 5 degrees to the l e f t or r i g h t of the center of the bowl i n t h i s study ( f o r the l e f t and r i g h t eye r e s p e c t i v e l y ) . The p a t t e r n surrounds an area t h a t subtends approximately 2 degrees of v i s u a l angle at the viewing d i s t a n c e of 30 cm and the 4 dots surround the t a r g e t l i g h t i n a diamond p a t t e r n . The l i g h t for t h i s p a t t e r n i s d e r i v e d from the f i l t e r wheel housing v i a a f i b e r o p t i c s bundle. A brass p l a t e with 4 pinhole i s i n s e r t e d a t the d i s t a l end of the path and i t forms the 4 dot p a t t e r n . An o b j e c t i v e lens and diaphragm at the d i s t a l end of t h i s pathway c o n t r o l the focus and b r i g h t n e s s of these d o t s . Background Luminance. The background luminance i s provided by an Osram XBO-150 watt xenon a r c lamp which has a c o l o r temperature of approximately 5300K when used i n t h i s perimeter ( i . e . , with the use of the r e f l e c t i v e s u r f a c e of the bowl and the f r o n t b a f f l e s ) . I t i s housed i n a fan-cooled L e i t z 250 housing which i s mounted to the r i g h t and behind the bowl on an aluminum p l a t f o r m . T h i s lamp i s powered by a L e i t z lamp supply (model Vx 1 5 0 - l f - 2 6 - L ) . The l i g h t from t h i s source i s d i r e c t e d from the lamp along an enclosed aluminum pathway with the use of f r o n t s u r f a c e m i r r o r s . Two f r o n t s u r f a c e m i r r o r s d i r e c t the l i g h t onto the top inner s u r f a c e of the bowl. From t h i s p o i n t , the l i g h t r a d i a t e s a c r o s s the e n t i r e s u r f a c e of the bowl i n accordance with the U l b r i c h t sphere p r i n c i p l e . The amount of background luminance i s c o n t r o l l e d by a diaphragm a t the f r o n t of the lamp housing; i t was set to a l l o w a c o n s i s t e n t luminance of 200 cd m - 2 for the e n t i r e study. Target Luminance. The t a r g e t luminance i s provided by a Ushio (ozone free) 75-watt xenon arc lamp which i s housed i n a modified ( i . e . i n c l u d e s a custom designed bulb holder and rear r e f l e c t o r ) , blower cooled O r i e l u n i v e r s a l housing (model II6144, 68 mm a p e r t u r e , f/0.7 pyrex lens) which i s l o c a t e d to the l e f t and rear of the bowl. This source i s powered by an O r i e l lamp supply (model II8500). From the lamp housing, the l i g h t i s d i r e c t e d through a +6.5 d i o p t e r lens i n t o an aluminum housing which holds a f i l t e r wheel f o r the narrow bandpass f i l t e r s . The f i l t e r wheel p l a c e s the f i l t e r s i n the pathway of the t a r g e t luminance. These i n t e r f e r e n c e f i l t e r s have bandwidths (at half-maximum tr a n s m i s s i o n ) of approximately 10 nanometers and have peak wavelengths which range from A 420.88 nm to A 651.00 nm (f o r s p e c i f i c d e s c r i p t i o n s of these f i l t e r s , r e f e r to Appendix A). There are 24 p o s s i b l e f i l t e r s ; 21 are used f o r the achromatic r e t i n a l t h r e s h o l d s and 16 are used f o r the chromatic r e t i n a l t h r e s h o l d s ( r e f e r to Appendix A). The f i l t e r wheel has 8 f i l t e r s l o t s so t e s t i n g i s completed i n groups of 8 wavelengths. At the f r o n t of t h i s f i l t e r housing, there i s a s l o t which holds n e u t r a l d e n s i t y f i l t e r s . A one, two or three l o g n e u t r a l d e n s i t y f i l t e r can be i n s e r t e d i n t o the l i g h t path at t h i s p o i n t . These n e u t r a l d e n s i t y f i l t e r s c o n t r o l the luminance of the t a r g e t over a 3 l o g u n i t range. The Goldmann perimeter a l s o has a s e r i e s of n e u t r a l d e n s i t y f i l t e r s which a l l o w f o r the r e d u c t i o n of the t a r g e t luminance by 2 l o g u n i t s i n 0.10 log u n i t s t e p s . The combination of these 2 systems allows f o r the c o n t r o l of the t a r g e t luminance over a 5 l o g u n i t range. As the l i g h t leaves the f i l t e r wheel housing, i t i s d i r e c t e d onto the bowl by a pantograph arm which c o n s i s t s of a s e r i e s of f r o n t s u r f a c e m i r r o r s , f o c u s i n g lenses and a prism. The pantograph arm can be p r e c i s e l y a d j u s t e d to place the t a r g e t at s p e c i f i c l o c a t i o n s across the hemispheric bowl. For the f o v e a l t h r e s h o l d s obtained here, the t a r g e t was p r o j e c t e d at 5 degrees e i t h e r to the l e f t or r i g h t of the center of the bowl ( f o r t e s t i n g the l e f t and r i g h t eye r e s p e c t i v e l y ) . The t a r g e t i s an oval which i s 1 m i l l i m e t e r i n diameter across i t s h o r i z o n t a l a x i s . (The area of the t a r g e t i s approximately 1.194 mm c a l c u l a t e d by the formula, 0.76 x /TT' x a where a=l/2 le n g t h of the major a x i s ) . F l i c k e r . F l i c k e r of the t a r g e t luminance i s provided by a stepper motor d r i v e n chopper. The chopper speed can be s e l e c t e d as one of two f i x e d f r e q u e n c i e s , nominally 1 and 24 Hz; a 1 Hz p r e s e n t a t i o n was used f o r chromatic r e t i n a l t h r e s h o l d s and a 24 Hz p r e s e n t a t i o n was used f o r achromatic r e t i n a l t h r e s h o l d s . P h o t o m e t e r A S p e c t r a P r i t c h a r d P h o t o m e t e r ( m o d e l 1 9 8 0 A ) was u s e d t o c a l i b r a t e b o t h t h e t a r g e t a n d b a c k g r o u n d l u m i n a n c e s o n c e p e r week d u r i n g t h e t e s t i n g p e r i o d s . I t h a s c o r r e c t i o n f a c t o r s w h i c h c o r r e c t t h e s p e c t r a l s e n s i t i v i t y t o V A f o r b o t h p h o t o p i c a n d s c o t o p i c c o n d i t i o n s ; t h e p h o t o p i c c o r r e c t i o n was a p p r o p r i a t e f o r t h e t e s t i n g c o n d i t i o n s u s e d i n t h i s s t u d y . A d j u s t m e n t s w e r e made when n e c e s s a r y t o m a i n t a i n t h e b a c k g r o u n d l u m i n a n c e a t 200 c d m~2 ( w i t h t h e u s e o f t h e d i a p h r a g m ) a n d t o m a x i m i z e t h e o u t p u t o f s h o r t w a v e l e n g t h e n e r g y i n t h e t a r g e t s o u r c e w i t h o u t s e r i o u s l y a f f e c t i n g t h e o u t p u t a t t h e o t h e r w a v e l e n g t h s . T h i s was a c c o m p l i s h e d b y a d j u s t i n g t h e m i r r o r s w i t h i n t h e t a r g e t h o u s i n g . S u b j e c t s G E N E R A L A l l o f t h e s u b j e c t s h a d n o r m a l t r i c h r o m a t i c c o l o r v i s i o n , a n d u n c o r r e c t e d o r c o r r e c t e d v i s u a l a c u i t y o f n o t l e s s t h a n 2 0 / 4 0 . S i n c e one o f t h e o b j e c t i v e s o f t h i s s t u d y i s t o e x a m i n e t h e i n f l u e n c e o f t h e n o r m a l ( i . e . i n t h e a b s e n c e o f p a t h o l o g i c a l c o n d i t i o n s ) a g i n g p r o c e s s , s u b j e c t s w e r e q u e s t i o n e d a b o u t t h e i r g e n e r a l h e a l t h . T h i s was a c c o m p l i s h e d w i t h a b r i e f q u e s t i o n n a i r e a b o u t t h e i r f a m i l y a n d p e r s o n a l h e a l t h h i s t o r y ( A p p e n d i x B ) . P a r t i c u l a r a t t e n t i o n was p a i d t o b o t h o c u l a r a n d s y s t e m i c c o n d i t i o n s a n d t h e e x t e n d e d u s e o f c e r t a i n d r u g s t h a t a r e k n o w n t o d i r e c t l y a f f e c t v i s u a l p e r f o r m a n c e ( e . g . c a t a r a c t s , d i a b e t e s m e l l i t u s , t h e e x t e n d e d u s e o f o r a l c o n t r a c e p t i v e s ) . E X P E R I M E N T I F i f t y one s u b j e c t s r a n g i n g i n a g e f r o m 13 t o 82 y e a r s w e r e t e s t e d f o r t h i s l i f e s p a n s t u d y . Two s u b j e c t s w e r e u n a b l e t o c o m p l e t e t h e t a s k a n d t h e r e f o r e t h e i r d a t a c o u l d n o t be i n c l u d e d (one 27 y e a r o l d f e m a l e a n d one 72 y e a r o l d f e m a l e ) . I n a d d i t i o n , s i n c e o n l y t w o y o u n g a d o l e s c e n t s w e r e t e s t e d ( i . e . one 13 a n d one 15 y e a r o l d ) , t h e r e was n o t e n o u g h d a t a f o r a n a d o l e s c e n t g r o u p . I t w a s , t h e r e f o r e , d e c i d e d t h a t t h e i r d a t a w o u l d n o t be i n c l u d e d . The f i n a l d a t a s e t was c o m p o s e d o f 47 s u b j e c t s r a n g i n g i n a g e f r o m 17 t o 82 y e a r s o f a g e . T h e s e s u b j e c t s w e r e a r r a n g e d i n t o s e v e n a g e g r o u p s a c c o r d i n g t o d e c a d e w i t h t h e e x c e p t i o n o f t h e s u b j e c t s i n t h e i r s e v e n t i e s a n d e i g h t i e s . T h e s e t w o a g e g r o u p s f o r m e d one age g r o u p ( i . e . o v e r 70 y e a r s ) s i n c e o n l y f o u r s u b j e c t s i n t h e i r e i g h t i e s w e r e t e s t e d . T h e r e w e r e b e t w e e n 5 t o 11 s u b j e c t s i n e a c h a g e g r o u p . An a t t e m p t was made t o o b t a i n e q u a l n u m b e r s o f f e m a l e s a n d m a l e s i n e a c h a g e g r o u p a l t h o u g h t h i s was n o t a l w a y s p o s s i b l e . I t was more d i f f i c u l t t o o b t a i n m a l e s u b j e c t s t h a n f e m a l e o n e s f o r m o s t age g r o u p s . R e f e r t o T a b l e s 1 a n d 2 a n d F i g u r e 2 f o r f u r t h e r d e t a i l s on s u b j e c t d e m o g r a p h i c s . R e c r u i t m e n t C o l l e g e a g e s t u d e n t s w e r e r e c r u i t e d t h r o u g h t h e d e p a r t m e n t a l s u b j e c t p o o l . A d s w e r e a l s o p l a c e d i n t h e Figure 2. Subject d i s t r i b u t i o n by age and sex. 3 8 Table 1. The d i s t r i b u t i o n of the subjects by sex for the seven age groups. G r o u p Age Females Males T o t a l I I I I I I IV V VI V I I TOTALS 1 7 - 2 " 2 1 - 3 9 3 9 - 3 9 4 9 - 4 9 5 9 - 5 9 6 9 - 6 9 7 9 + 3 « 17 1 ] 47 Table 2. The average ages of the subjects in the seven age groups. G r o u p Age F e m a l e s Males O v e r a l l Range A v g Age Avg Age Avg Age I 1 7 - 2 8 1 8 . 7 5 II 2 1 - 3 9 2 2 . 5 9 I I I 3 9 - 3 9 3 1 . 5 9 IV 4 9 - 4 9 4 4 . 9 9 V 5 9 - 5 9 5 2 . 5 9 V I 6 9 - 6 9 6 4 . 7 5 V I I 79+ 7 7 . 6 3 u n i v e r s i t y papers to r e c r u i t s u b j e c t s across the e n t i r e age span r e q u i r e d . Subjects i n the over 60 age group were r e c r u i t e d through l o c a l s e n i o r s ' c e n t e r s . Information about the study was presented to the s e n i o r s ' groups through t a l k s and p o s t e r s at v a r i o u s r e c r e a t i o n c e n t e r s . Other s u b j e c t s were r e c r u i t e d through the department, c o n t a c t s at the u n i v e r s i t y and f r i e n d s and f a m i l y of the l a b per s o n n e l . EXPERIMENT II The s u b j e c t s were three undergraduate s t u d e n t s , one male (SI) and two females (S2 & S3). SI and S3 were both 22 years o l d and S2 was 21 years o l d . A l l s u b j e c t s were emmetropes and a l l had normal t r i c h r o m a t i c v i s i o n . None of the s u b j e c t s had any known h e a l t h problems t h a t might a f f e c t t h e i r v i s u a l performance. Procedure GENERAL A l l s u b j e c t s were t e s t e d for v i s u a l a c u i t y on the Bausch and Lomb O r t h o r a t e r and monocularly on the S n e l l e n A c u i t y Chart. They were a l s o assessed monocularly f o r normal c o l o r v i s i o n with the I s h i h a r a and/or Dvorine Pseudoisochromatic P l a t e s . Achromatic and chromatic r e t i n a l t h r e s h o l d s were assessed f o r one eye per s u b j e c t using the BCUP under f u l l y p h otopic c o n d i t i o n s (200 cd m - 2 a d a p t a t i o n f i e l d ) . EXPERIMENT I When v i s u a l a c u i t y and c o l o u r v i s i o n were e q u i v a l e n t i n each eye, assignment to the l e f t or r i g h t eye c o n d i t i o n was random. However, i f one eye was s u p e r i o r i n t h i s r e s p e c t or i f there was an oc u l a r pathology or degeneration i n one eye, the b e t t e r eye was used for t e s t i n g . EXPERIMENT II In a d d i t i o n to the general p r o t o c o l o u t l i n e d above, these 3 s u b j e c t s were a l s o t e s t e d f o r v i s u a l a c u i t y with La n d o l t Ring A c u i t y Charts and f u r t h e r c o l o r v i s i o n t e s t i n g was completed using the Farnsworth 100-Hue Test, Nomenclature Test, and the P i c k f o r d - N i c o l s o n Anomaloscope. These s u b j e c t s were randomly assigned to have e i t h e r t h e i r l e f t or r i g h t eye t e s t e d for r e t i n a l t h r e s h o l d s ; SI had h i s l e f t eye t e s t e d and S2 and S3 both had t h e i r r i g h t eyes t e s t e d . These assignments were maintained throughout the r e t i n a l t h r e s h o l d t e s t i n g procedures. T e s t i n g S e s s i o n GENERAL The stimulus and t a r g e t sources were s t a b i l i z e d p r i o r to each t e s t i n g s e s s i o n . The room l i g h t was e x t i n g u i s h e d except f o r a dim red l i g h t on the operator s i d e of the perimeter. Subjects were seated a t the perimeter and the height of the s t o o l and the c h i n r e s t were adjusted to ensure that the s u b j e c t was comfortable and that the eye to be t e s t e d was centered on the perimeter telescope. This maintained the distance from the cornea to the t e s t i n g surface at 30 cm. The other eye was covered with an opaque, white occluder. Subjects remained i n f r o n t of the perimeter fo r a f i v e minute preadaptation p e r i o d . During t h i s time the operator readied the instrument for t e s t i n g and explained and demonstrated the task to the subject. At the end of t h i s p e r i o d , the diameter of the subjects p u p i l was measured through the perimeter t e l e s c o p e . Throughout the t e s t i n g procedure, the subject's eye movements were monitored through the telescope. The t a r g e t stimulus was presented w i t h i n the 4 dot f i x a t i o n area 5 degrees to e i t h e r the l e f t or r i g h t of the center of the bowl ( i . e . , the c e n t r a l telescope) to t e s t the l e f t or r i g h t eye r e s p e c t i v e l y . Each session began with a t r a i n i n g phase to f a m i l i a r i z e the subjects with the dichotomy between c o l o r and f l i c k e r i n the achromatic ( f l i c k e r ) c o n d i t i o n . For experiment I, the achromatic c o n d i t i o n was always completed f i r s t i n order to avoid confuse about the c o l o r / f l i c k e r d i s t i n c t i o n . For both achromatic and chromatic procedures, a l l thresholds were obtained using an ascending method of l i m i t s ( i . e . , s t i m u l i were presented from subthreshold l e v e l s with i n c r e a s i n g luminance u n t i l the threshold was r e a l i z e d ) . Each tar g e t wavelength was displayed so that i t could be seen c l e a r l y by the s u b j e c t . A l s o , i n the case of the achromatic c o n d i t i o n , i t was v e r i f i e d that the subject could detect the f l i c k e r . The t a r g e t luminance was then 42 decreased to a point well below the expected threshold for the subject. It was confirmed with the subject that the target stimulus was no longer v i s i b l e to them. The operator then gradually increased the target luminance in 0.1 log unit steps, allowing a 30 second exposure at each step u n t i l the subject responded that the target had been detected. Subjects were asked to respond when they could f i r s t detect the f l i c k e r for the achromatic condition (although they may ac t u a l l y have detected the color f i r s t ) and when they could f i r s t detect the colour in the chromatic condition. Subjects were allowed a rest after each 8 wavelengths during which time they remained seated at the perimeter (to maintain the adaptation l e v e l ) . Subjects were encouraged to avert their eyes or blink between t r i a l s as this appeared to reduce fatigue and the Ganzfeld e f f e c t . EXPERIMENT II The general testing session protocol was also followed for t h i s experiment but with the following changes. For this experiment, the perimeter was f i t t e d with a custom-made f i l t e r and lense holder which was used to interpose gelatin f i l t e r s in the subjects' visual path. The f i l t e r holder was attached to the chin rest and the subjects viewed the target through the f i l t e r held by i t . These f i l t e r s were used to mimic the aged-related changes seen in the human c r y s t a l l i n e lens. Lee 81A polyester-based f i l t e r s were used because they c l o s e l y approximated the transmission c h a r a c t e r i s t i c s e s t a b l i s h e d f o r the i n v i v o human c r y s t a l l i n e lens at three p o i n t s across the l i f e s p a n (Said & Weale, 1959) ( r e f e r to F i g u r e 3 and the t r a n s m i s s i v i t y c h a r a c t e r i s t i c s i n Appendix C). There were 12 t e s t i n g c o n d i t i o n s (6 f o r each achromatic and chromatic) ( r e f e r to Table 3 f o r a complete l i s t i n g of the experimental c o n d i t i o n s with p r e r e c e p t o r a l f i l t e r s ) . C o n d i t i o n 0 was the "without f i l t e r " c o n d i t i o n ; r e t i n a l t h r e s h o l d s were assessed with none of these p r e r e c e p t o r a l f i l t e r s i n p l a c e . The experimental c o n d i t i o n s were as f o l l o w s : c o n d i t i o n 1 was with 1 f i l t e r (Y%=82.54), c o n d i t i o n 2 was with 2 p r e r e c e p t o r a l f i l t e r s (Y%=63.87), c o n d i t i o n 3 was with 3 p r e r e c e p t o r a l f i l t e r s (Y%=50.50), c o n d i t i o n 4 was with 4 p r e r e c e p t o r a l f i l t e r s (Y%=38.89) and c o n d i t i o n 5 was with a 0.50 n e u t r a l d e n s i t y f i l t e r (Y%=46.92) ( t h i s n e u t r a l d e n s i t y f i l t e r was chosen because i t had a Y% t r a n s m i s s i o n intermediate between the Y% for the 3 and 4 p r e r e c e p t o r a l f i l t e r c o n d i t i o n s ) ( r e f e r to Appendix C and F i g u r e 3 f o r f u r t h e r d e t a i l s on these f i l t e r s ) . The order of the p r e s e n t a t i o n of these c o n d i t i o n s was randomized, although a l l 1 of the s u b j e c t s were t e s t e d f i r s t i n the "without f i l t e r " achromatic c o n d i t i o n . Subjects were t e s t e d at l e a s t twice on both the "without f i l t e r " achromatic and chromatic procedures before proceeding to any of the "with f i l t e r " c o n d i t i o n s i n an attempt to s t a b i l i z e responding. The p r e s e n t a t i o n order of the wavelengths w i t h i n each t e s t i n g s e s s i o n remained con s t a n t . In the "without f i l t e r " c o n d i t i o n , each t a r g e t wavelength was t e s t e d 5 times per t r i a l . For the "with f i l t e r " c o n d i t i o n , each t a r g e t wavelength was t e s t e d 3 times with the p r e r e c e p t o r a l f i l t e r ( s ) i n place and 3 times without them i n place i n a counterbalanced order. T e s t i n g s e s s i o n s were u s u a l l y l i m i t e d to e i t h e r a f u l l achromatic (21 f i l t e r s ) t e s t or a f u l l chromatic (16 f i l t e r s ) t e s t to reduce the e f f e c t s of su b j e c t f a t i g u e . Only S2 completed a l l the t e s t i n g c o n d i t i o n s . Subject S3 d i d not complete c o n d i t i o n 1 f o r e i t h e r the achromatic or chromatic t h r e s h o l d s and SI d i d not complete c o n d i t i o n 1 for the achromatic t h r e s h o l d s . C o n d i t i o n 1 represented the r s i m u l a t i o n of the a c t u a l age of the s u b j e c t s and t h e r e f o r e was not con s i d e r e d as important as the other c o n d i t i o n s . Table 3 TESTING CONDITIONS FOR EXPT II C o n d i t i o n Aging F i l t e r s 0 none 1 1 f i l t e r 2 2 f i l t e r s 3 3 f i l t e r s 4 4 f i l t e r s 5 0.50 N.D. f i l t e r Data Conversion The raw data c o l l e c t e d from the BCUP at each wavelength c o n s i s t s of a value f o r the n e u t r a l d e n s i t y f i l t e r u t i l i z e d to reduce the t a r g e t luminance t o w i t h i n the t h r e s h o l d range and a value f o r the p o s i t i o n of the Goldmann n e u t r a l d e n s i t y f i l t e r s a t the point when the t h r e s h o l d i s achieved. These values are recorded i n candelas per square meter (cd m z ) . The c a l i b r a t i o n values recorded weekly with the P r i t c h a r d Photometer are a l s o recorded i n cd m"2. Both sets of values 45 Figure 3 ( a ) . Measured o p t i c a l d e n s i t i e s of human lenses across the v i s i b l e spectrum for four ages. (Sold ic W«xjle. 1959) 1 5 o t E 400 ACE1 WAVELENGTH ( n a n o m « t o r » ) + AGE2 * AGE3 AGE4 F i g u r e 3 (b). O p t i c a l d e n s i t i e s of age s i m u l a t i o n f i l t e r s a c r oss the v i s i b l e spectrum f o r four ages and a 0.50 n e u t r a l d e n s i t y f i l t e r , i to 5 a i 0.9 -0.8 -ND = 0.50 n e u t r a l d e n s i t y f i l t e r ACE1 WAVELENGTH (nanorrwtera) AGE2 • ACE3 A A0E4 N00 46 are converted to log cd m~ z values . The a c t u a l t h r e s h o l d v a l u e s , however, are u s u a l l y presented i n quanta d e g _ 2 s e c ~ l . To o b t a i n these f i n a l v a l u e s , the r e c o r d e d Goldmann v a l u e s , the c a l i b r a t i o n values f o r each wavelength and the s u b j e c t p u p i l diameter are used for a s e r i e s of c a l c u l a t i o n s which r e s u l t i n the t h r e s h o l d values which are expressed i n quanta d e g - 2 s e c - l . A computer program was designed to accomplish these c a l c u l a t i o n s and to produce graphs of the r e t i n a l t h r e s h o l d s . The i n i t i a l c a l c u l a t i o n program produces a t h r e s h o l d value along with the standard d e v i a t i o n f o r the readings at each wavelength. The graphing program i n v o l v e s an e s t i m a t i o n of instrumental e r r o r s (e.g., e r r o r s due to the use of d i s c r e t e luminance s t e p s , problems with p u p i l diameter e s t i m a t i o n and source c a l i b r a t i o n e r r o r ) . T h i s e r r o r e s t i m a t i o n was used as p a r t of the c u r v e - f i t t i n g r o u t i n e designed for t h i s data. The e r r o r bars on graphs f o r i n d i v i d u a l subjects were based on these e s t i m a t i o n s . Experimental Design EXPERIMENT I (1) Subjects: 47 normal t r i c h r o m a t i c s u b j e c t s ranging in age from 17 to 82 years of age. There were 30 female subjects and 17 male s u b j e c t s . (2) Constant C o n d i t i o n s : (a) Adaptation f i e l d luminance - 200 cd m~2 (b) Stimulus s i z e - 1 mm a c r o s s the h o r i z o n t a l a x i s . (3) Independent V a r i a b l e s : (a) Between s u b j e c t s v a r i a b l e - age, grouped by decade (b) Within s u b j e c t s v a r i a b l e -( i ) Achromatic c o n d i t i o n had 21 wavelengths ( i i ) Chromatic c o n d i t i o n used 16 wavelengths (4) Dependent V a r i a b l e : the stim u l u s luminance i n t e n s i t y r e q u i r e d f o r the s u b j e c t to d e t e c t the t a r g e t s t i m u l u s , A L ( i ) In the achromatic c o n d i t i o n , s u b j e c t s responded when they c o u l d d e t e c t the f l i c k e r of the stimulus ( i i ) In the chromatic c o n d i t i o n , s u b j e c t s responded when they could d e t e c t the c o l o r of the stimulus EXPERIMENT II (1) S u b j e c t s : 3 young emmetropic students (ages 21 and 22 years) with normal t r i c h r o m a t i c c o l o r v i s i o n . One s u b j e c t was male and the other two were female. (2) Constant C o n d i t i o n s : (a) Adaptation f i e l d luminance - 200 cd m - 2 (b) Stimulus s i z e - 1 mm ac r o s s the h o r i z o n t a l a x i s . (3) Independent V a r i a b l e s : (a) Between s u b j e c t s v a r i a b l e - age s i m u l a t i o n f i l t e r s ( c o n d i t i o n s 0 to c o n d i t i o n 5, r e f e r to Table 5) (b) Within s u b j e c t s v a r i a b l e -( i ) Achromatic c o n d i t i o n had 21 wavelengths ( i i ) Chromatic c o n d i t i o n used 16 wavelengths (4) Dependent V a r i a b l e : the stimulus luminance i n t e n s i t y r e q u i r e d f o r the subject to d e t e c t the t a r g e t s t i m u l u s , A L ( i ) In the achromatic c o n d i t i o n , s u b j e c t s responded when they could d e t e c t the f l i c k e r of the stimulus ( i i ) In the chromatic c o n d i t i o n , s u b j e c t s responded when they could d e t e c t the c o l o r of the stimulus R e s u l t s Both achromatic and chromatic r e t i n a l t h r e s h o l d s were e s t a b l i s h e d under photopic c o n d i t i o n s f o r sub j e c t s ranging i n age from 17 to 82 years. When examining t h i s type of data, i t i s important to c l e a r l y e s t a b l i s h c e r t a i n parameters about these f u n c t i o n s ; the r e l a t i o n s h i p between r e t i n a l t h r e s h o l d s and s p e c t r a l s e n s i t i v i t y , what i s meant by higher and lower and what i s meant by log u n i t l o s s . R e t i n a l t h r e s h o l d s are i n v e r s e l y r e l a t e d to s p e c t r a l s e n s i t i v i t i e s ; a lower r e t i n a l t h r e s h o l d i n d i c a t e s a higher 49 s p e c t r a l s e n s i t i v i t y . Secondly, because t h i s data i s presented on an i n v e r t e d log s c a l e o r d i n a t e a x i s , the r e l a t i v e terms higher and lower have meanings which are opposite to common p r a c t i c e . A higher r e t i n a l t h r e s h o l d r e f e r s to one which i s f a r t h e r down the o r d i n a t e a x i s than another whereas a lower r e t i n a l t h r e s h o l d r e f e r s to one which i s f a r t h e r up the o r d i n a t e with r e s p e c t to another. F i n a l l y , l o g u n i t l o s s w i l l be used h e r e i n to r e f e r to r e t i n a l t h r e s h o l d s which are higher with r e s p e c t to others s i n c e higher t h r e s h o l d s represent a l o s s i n v i s u a l f u n c t i o n . EXPERIMENT I Achromatic Data G r a p h i c a l A n a l y s i s The curves f o r the achromatic data f o r a l l s u b j e c t s f o l l o w a s i m i l a r p a t t e r n ; a unimodal f u n c t i o n which i s a broad, i n v e r t e d U-shaped curve ( r e f e r to F i g u r e 4, a - g). In the present study, the s i n g l e peak ( i . e . , lowest t h r e s h o l d ) f o r t h i s f u n c t i o n f e l l somewhere between A 537 nm and A 576 nm; f o r 53% (25 s u b j e c t s ) of the s u b j e c t s the peak was a t A 537 nm, for 28% (13 s u b j e c t s ) of them, i t was at A 545 nm, f o r 8.5% (4 s u b j e c t s ) of them i t was at A 560 nm, f o r 6.3% (3 s u b j e c t s ) of them i t was at A 576 nm and for 1 s u b j e c t the peak was spread from A 537 to A 545 nm. The highest t h r e s h o l d s ( i . e . , lowest s e n s i t i v i t y ) on the curve i n the long-wavelength range of the spectrum was at A 651 nm f o r a l l s u b j e c t s . However, the h i g h e s t t h r e s h o l d s on the curve i n the short-wavelength range were extremely v a r i a b l e . For many of the s u b j e c t s , e s p e c i a l l y those i n the o l d e r age groups, there was o f t e n not enough energy a v a i l a b l e f o r them to d e t e c t the f l i c k e r i n the extreme short-wavelength s t i m u l i ; 34% of the s u b j e c t s were able to d e t e c t a l l of the blue s t i m u l i ( i . e . , to A 420 nm), 28% were able to d e t e c t the s t i m u l i to A 436 nm, 2% to A 441 nm, 25% to A 456 nm and the f i n a l 11% were able to d e t e c t the blue s t i m u l i only to A 472 nm. For the g r a p h i c a l a n a l y s i s , the curve for each s u b j e c t was extended to the p o i n t where they were l a s t able to d e t e c t the f l i c k e r i n the t a r g e t s t i m u l i . For comparative purposes and s t a t i s t i c a l a n a l y s i s , however, the data was c u r t a i l e d to i n c l u d e data o n l y up to the l a s t blue s t i m u l i that was de t e c t e d by a l l s u b j e c t s . T h i s value was A 472 nm and i t was u t i l i z e d as the s t a r t i n g p o i n t f o r the short-wavelength range of the spectrum f o r comparative and s t a t i s t i c a l a n a l y s e s . The h i g h e s t t h r e s h o l d s on the curves a t the extreme for the sh o r t and long wavelength s t i m u l i tended to be approximately e q u i v a l e n t f o r the younger four groups. Beginning with Group 5, however, the high v a l u e s i n the s h o r t wavelength range increased ( i . e , the t h r e s h o l d s i n the blue range were comparatively higher than those i n the long wavelength range). For Group 7, t h i s represented a 0.56 log u n i t d i f f e r e n c e between the high p o i n t s f o r the s h o r t and long wavelength e n e r g i e s ( i . e . , A 487 and A 651 nm Figure 4 (a - g). Data d i s t r i b u t i o n within each individual age group for achromatic r e t i n a l increment thresholds. 39 s-l o V9 55 r e s p e c t i v e l y ) . The extreme range of the data can be d e s c r i b e d by comparing the data f o r the curve with the lowest o v e r a l l r e t i n a l t h r e s h o l d s a g a i n s t the curve with the highest o v e r a l l r e t i n a l t h r e s h o l d s . The data f o r these two curves were obtained f o r a 24 year old male and a 81 year o l d female s u b j e c t r e s p e c t i v e l y . The d i f f e r e n c e between these two curves i s d e s c r i b e d by a 1.75 l o g u n i t l o s s i n the blue ( i . e . , A 4 7 2 nm), a 0.99 and 0.72 l o g u n i t l o s s at A 537 and A 545 nm r e s p e c t i v e l y , and a 0.88 log u n i t l o s s at A 651 nm. The curve with the g r e a t e s t peak (where *greatest'= the lowest r e t i n a l t h r e s h o l d s / t h e h i g h e s t s p e c t r a l s e n s i t i v i t y ) (7.53 log u n i t s at A 545 nm) was obtained f o r a 61 year old female. The g r e a t e s t value i n the blue range (8.774 l o g u n i t s at A 420 nm) was obtained f o r a 22 year o l d female and the lowest value i n the red range (8.744 l o g u n i t s at A 651 nm) was obtained f o r a 21 year old female. Group Average Data. In g e n e r a l , the averaged group data i n d i c a t e s t hat there i s a gradual increase i n r e t i n a l t h r e s h o l d s ( i . e . , a decrease i n s e n s i t i v i t y ) f o r the achromatic f u n c t i o n with advancing age ( r e f e r to F i g u r e s 5 & 6 a to g ) . Two exceptions to t h i s are noted. The lowest r e t i n a l t h r e s h o l d s ( i . e . , the g r e a t e s t s e n s i t i v i t y ) were found f o r Group 2 (21 to 29 year o l d s ) , although the t h r e s h o l d s f o r Group 1 (17 to 20 year olds) were only s l i g h t l y h i gher. The data for Group 2, t h e r e f o r e , w i l l be used as the b a s i s f o r comparison with the other groups. The r e t i n a l t h r e s h o l d s f o r Group 4 (40 to 49 year olds) were s l i g h t l y lower than the t h r e s h o l d s f o r Group 3 (30 to 39 year o l d s ) except i n the red r e g i o n where they were s l i g h t l y h i g h e r . The remaining curves f o l l o w e d a s e q u e n t i a l p a t t e r n with r e s p e c t to advancing age ( i . e . , o l d e r groups had higher t h r e s h o l d s ) . The curves f o r the f i r s t 5 groups (up to and i n c l u d i n g the 50 to 59 year o l d group) a l l l i e q u i t e c l o s e together; the spread between these curves i s l e a s t i n the red r e g i o n beyond 622 nm; the spread between the upper and lower curves f o r these f i v e groups at A 651 nm i s 0.045 l o g u n i t s . The spread, however, i s somewhat greater between A 590 and A 622 nm (e.g., there i s a 0.18 l o g u n i t spread between the upper and lower p o i n t s f o r these 5 groups at A 611 nm). The spread i s even s l i g h t l y more increased i n the blue r e g i o n e s p e c i a l l y f o r the 50 to 59 year old group with r e s p e c t to the other four groups (e.g., the spread at A 472 nm i s 0.34 l o g u n i t s ) . The o l d e s t two groups show a g r e a t e r spread from the other f i v e groups. The thresholds f o r Group 6 are s t i l l reasonably c l o s e to the f i r s t f i v e groups although the spread has become more pronounced i n the green r e g i o n (e.g., the average t h r e s h o l d at A 545 nm i s 0.25 l o g u n i t s higher than the lowest group t h r e s h o l d and i s 0.19 l o g u n i t s higher than the average t h r e s h o l d for Group 5). T h i s r e p r e s e n t s an o v e r a l l r e d u c t i o n i n the height of t h e p e a k o f t h e c u r v e f o r G r o u p 6 . The s p r e a d b e t w e e n t h e t h r e s h o l d s f o r t h e f i r s t s i x g r o u p s i s g e n e r a l l y w i t h i n t h e s t a n d a r d d e v i a t i o n r a n g e . The t h r e s h o l d s f o r G r o u p 7 , h o w e v e r , a r e s u b s t a n t i a l l y h i g h e r t h a n t h e t h r e s h o l d s f o r t h e y o u n g e r t w o g r o u p s a n d t h i s d i f f e r e n c e i s w e l l b e y o n d t h e s t a n d a r d d e v i a t i o n s ; t h e d i f f e r e n c e b e t w e e n t h e t h r e s h o l d s f o r G r o u p 7 a n d t h e s e g r o u p s i s a t l e a s t one s t a n d a r d d e v i a t i o n f o r a l l w a v e l e n g t h s ( r e f e r t o F i g u r e 6 , a t o g ) . T h i s d i f f e r e n c e i s t h e l e a s t a t t h e r e d e n d ( 0 . 3 8 t o l o g u n i t d i f f e r e n c e a t A 651 nm) a n d t h e g r e a t e s t i n t h e b l u e e n d ( 1 . 2 8 l o g u n i t d i f f e r e n c e a t A 487 n m ) . I n g e n e r a l , t h e s p r e a d b e t w e e n a l l o f t h e o t h e r g r o u p s ( i . e . , o t h e r t h a n b e t w e e n t h e t w o y o u n g e r g r o u p s a n d t h e o l d e s t g r o u p ) a r e w i t h i n t h e s t a n d a r d d e v i a t i o n v a l u e s . One e x c e p t i o n t o t h e g e n e r a l t r e n d o f i n c r e a s e s i n r e t i n a l t h r e s h o l d s w i t h a d v a n c i n g a g e , p a r t i c u l a r l y i n t h e s h o r t w a v e l e n g t h r a n g e , s h o u l d be n o t e d . F o r G r o u p 7 , t h e a v e r a g e t h r e s h o l d v a l u e f o r t h e e x t r e m e s h o r t w a v e l e n g t h s t i m u l u s ( i . e . , A 472 nm) was l o w e r t h a n t h e a v e r a g e t h r e s h o l d v a l u e f o r t h e p r o x i m a l b l u e s t i m u l u s ( i . e . , A 487 nm) ( r e f e r t o F i g u r e 5 ) . T h i s a p p e a r s a s a s h a r p u p t u r n i n t h e d a t a d i s t r i b u t i o n a t t h e b l u e e n d o f t h e s p e c t r u m f o r t h i s g r o u p . T h i s u p t u r n a l s o a p p e a r e d i n some o f t h e d a t a f o r t h e i n d i v i d u a l s i n t h i s g r o u p b u t i t was much more g r a d u a l t h a n f o r t h e a v e r a g e d d a t a . 58 59 D i s t r i b u t i o n o f t h e D a t a w i t h i n e a c h G r o u p . I n g e n e r a l , t h e d a t a f o r t h e y o u n g e r age g r o u p s s h o w e d l e s s s p r e a d b e t w e e n t h e d a t a f o r t h e v a r i o u s s u b j e c t s w i t h i n t h e g r o u p t h a n t h e s u b j e c t s i n t h e o l d e r g r o u p s ( r e f e r t o F i g u r e 4 , a t o g ) . The p a t t e r n o f t h i s s p r e a d a l s o s h o w e d a c h a n g e w i t h a g e . The d a t a f o r t h e t w o y o u n g e s t a g e g r o u p s s h o w e d a s p r e a d b e t w e e n t h e s u b j e c t s t h a t was g r e a t e s t a t t h e s h o r t w a v e l e n g t h ( b l u e ) e n d o f t h e s p e c t r u m a n d l e a s t a t t h e l o n g w a v e l e n g t h ( r e d ) e n d o f t h e s p e c t r u m . F o r t h e 17 t o 20 y e a r o l d g r o u p ( G r o u p 1 ) , t h e s p r e a d a t t h e b l u e e n d ( i . e . , A 472 a n d A 436 nm r e s p e c t i v e l y ) o f t h e s p e c t r u m was a p p r o x i m a t e l y 4 t o 5 t i m e s a s g r e a t t h a n t h e s p r e a d a t t h e r e d e n d ( i . e . , A 651 nm) a n d a p p r o x i m a t e l y 2 . 5 t i m e s g r e a t e r t h a n t h e s p r e a d i n t h e g r e e n r a n g e ( i . e . , A 537 nm a n d 545 n m ) . T h i s r e p r e s e n t s a 0 . 7 4 l o g u n i t s p r e a d b e t w e e n t h e u p p e r a n d l o w e r s u b j e c t d a t a p o i n t s a t 436 nm, a 0 . 6 5 nm l o g u n i t s p r e a d a t A 472 nm, 0 . 2 7 a n d 0 . 2 3 a t A 537 a n d A 545 nm r e s p e c t i v e l y a n d a 0 . 1 6 l o g u n i t s p r e a d a t A 651 n m . The d a t a s p r e a d b e t w e e n t h e s u b j e c t s i n t h e 21 t o 29 y e a r o l d g r o u p ( G r o u p 2) was s l i g h t l y more s y m m e t r i c a l t h a n i t was f o r t h e f i r s t g r o u p ; t h e s p r e a d was s i m i l a r a t t h e b l u e e n d b u t g r e a t e r a t t h e r e d e n d o f t h e s p e c t r u m f o r G r o u p 2 t h a n i t was f o r t h e f i r s t g r o u p . F o r t h e s e c o n d g r o u p , t h e s p r e a d b e t w e e n t h e u p p e r a n d l o w e r d a t a p o i n t s a t t h e b l u e e n d was a p p r o x i m a t e l y t w i c e a s g r e a t t h a n i t was f o r e i t h e r t h e g r e e n a n d r e d r a n g e s o f t h e s p e c t r u m f o r t h a t g r o u p ( t h e s p r e a d s i n t h e g r e e n a n d r e d Fiqure 6 (a - g ). Group average data with standard deviation error bars Included. o CD* m oo" 5°. O O in <7>" , 400.0 450.0 o <D" in co' m oi' I 1 1 500.0 550.0 600.0 WAVELENGTH (NM) T 1 650.0 700.0 400.0 450.0 - 1 1 1 1 500.0 550.0 600.0 650.0 WAVELENGTH (NM) o Figure 6a. Group I Figure 6b. Group II Figure 6c. Group III Figure 6d. Group IV £9 ranges were approximately e q u i v a l e n t to one a n o t h e r ) . T h i s r e p r e s e n t s a 0.89 l o g u n i t spread between the upper and lower s u b j e c t data p o i n t s at A 436 nm, a 0.80 nm log u n i t spread at A 472 nm, 0.34 and 0.38 at A 537 and A 545 nm r e s p e c t i v e l y and a 0.38 log u n i t spread at A 651 nm. The next four age groups showed a more symmetrical spread across both ends of the spectrum than the f i r s t 2 groups d i d ; that i s , the spreads were more s i m i l a r a c r o s s the whole spectrum. For the 30 to 39 year o l d age group (Group 3), there were two important notes. F i r s t l y , the data f o r one of the s u b j e c t s was a s t r o n g o u t l i e r from the r e s t of the data. The range of the spreads for t h i s group w i l l t h e r e f o r e be r e p o r t e d both with and without the o u t l i e r data i n c l u d e d . Secondly, i t i s i n t e r e s t i n g to note t h a t t h i s was the only group that had fewer females than males (n=6; 2 females and 4 males) and the data for these two females was the lowest data f o r the group even though they were the youngest s u b j e c t s i n the group (one of these females was the s t r o n g o u t l i e r ) . With the o u t l i e r data i n c l u d e d , the spread a t the blue end ( i . e . , A 472 nm) i s approximately 1.5 times as great as the spread i n the green range ( i . e . , A 5 3 7 and 545 nm) and at the red end ( i . e . , A651 nm). This r e p r e s e n t s a 1.06 l o g u n i t spread between the upper and lower s u b j e c t data p o i n t s at A 472 nm (when one or more s u b j e c t s could not d e t e c t the f l i c k e r at A 436 nm, t h i s range was not r e p o r t e d ) , 0.69 and 0.65 l o g u n i t spread at A 537 and A 545 nm r e s p e c t i v e l y and a 0.82 l o g u n i t spread at 651 nm. With the o u t l i e r data removed, the spread i s only s l i g h t l y g r e a t e r at the blue end than i n the other ranges. T h i s r e p r e s e n t s a spread of 0.23 l o g u n i t between the upper and lower s u b j e c t data p o i n t s at 472 nm , 0.25 and 0.33 l o g u n i t spread at A 537 and A 545 nm r e s p e c t i v e l y and a 0.31 l o g u n i t spread a t A 651 nm. For Group 4 (40 to 49 y e a r s ) , the spread at the blue end was approximately 3 times as great as i n the green range and s l i g h t l y more than 3 times greater than i t was i n the red range of the spectrum. The spread at the red end was approximately twice as great as the spread i n the green range. This r e p r e s e n t s a 0.72 l o g u n i t spread between the upper and lower s u b j e c t data p o i n t s at A 472 nm, 0.25 and 0.32 at A 537 and A 545 nm r e s p e c t i v e l y and a 0.64 l o g u n i t spread at A 651 nm. For the 50 to 59 year o l d group (Group 5), the spread at the blue end ( i . e . , A 472) of the spectrum was approximately 3 times as great than the spread at the red end ( i . e . , A 651 nm) and approximately 2 times gr e a t e r than the spread i n the green range ( i . e . , A 537 nm and A 545 nm). The spread i n the green range was 1.5 to 2 times as great than at the red end. This r e p r e s e n t s a 1.04 l o g u n i t spread between the upper and lower s u b j e c t data p o i n t s at A 472 nm, 0.65 and 0.54 at A 537 and A 545 nm r e s p e c t i v e l y and a 0.36 l o g u n i t spread at A 651 nm. For the 60 to 69 year o l d group (Group 6), the spread between the upper and lower data p o i n t s was almost symmetrical; at the blue end of the ( A 472 nm) i t was about 1.4 and 1.2 t i m e s g r e a t e r t h a n t h e g r e e n r a n g e ( A 537 nm a n d A 545 nm r e s p e c t i v e l y ) a n d a b o u t 1 . 3 t i m e s a s g r e a t a s t h e s p r e a d a t t h e r e d e n d . T h i s r e p r e s e n t s a 1 . 2 2 l o g u n i t s p r e a d b e t w e e n t h e u p p e r a n d l o w e r s u b j e c t d a t a p o i n t s a t A 472 nm, 0 . 8 4 a n d 0 . 9 8 a t A 537 a n d A 545 nm r e s p e c t i v e l y a n d a 0 . 9 2 l o g u n i t s p r e a d a t A 651 nm. G r o u p 6 s h o w e d t h e g r e a t e s t o v e r a l l s p r e a d b e t w e e n s u b j e c t d a t a o f a l l t h e g r o u p s . F i n a l l y , t h e o l d e s t g r o u p ( G r o u p 7) s h o w e d a s p r e a d t h a t was s l i g h t l y l e s s a t t h e s h o r t w a v e l e n g t h ( b l u e ) e n d o f t h e s p e c t r u m t h a n a t t h e l o n g w a v e l e n g t h ( r e d ) e n d o f t h e s p e c t r u m . T h i s was t h e r e v e r s e o f t h e s i t u a t i o n f o r t h e y o u n g e r g r o u p s . The s p r e a d a t t h e b l u e e n d o f t h e s p e c t r u m was 0 . 7 6 a s much a s t h e s p r e a d a t t h e r e d e n d ( i . e . , t h e s p r e a d a t t h e r e d e n d was 1 . 3 t i m e s a s g r e a t a s t h e s p r e a d a t t h e b l u e e n d ) . The s p r e a d a t t h e b l u e e n d was a b o u t 1 . 3 t i m e s g r e a t e r t h a n t h e s p r e a d f o r t h e g r e e n r a n g e a n d t h e s p r e a d a t t h e r e d e n d was a b o u t 1 . 7 t i m e s a s g r e a t a s t h e s p r e a d i n t h e g r e e n r a n g e . T h i s r e p r e s e n t s a 0 . 7 4 l o g u n i t s p r e a d b e t w e e n t h e u p p e r a n d l o w e r s u b j e c t d a t a p o i n t s a t A 472 nm, 0 . 5 4 a n d 0 . 5 6 a t A 537 a n d A 545 nm r e s p e c t i v e l y a n d a 0 . 9 7 l o g u n i t s p r e a d a t A 651 nm. T h i s i s l e s s o f a s p r e a d i n t h e b l u e a n d g r e e n r a n g e s a n d a v e r y s l i g h t l y g r e a t e r s p r e a d a t t h e r e d e n d t h a n was f o u n d w i t h G r o u p 6 . The r a n g e o f t h e d a t a d i s t r i b u t i o n w i t h i n t h e v a r i o u s a g e g r o u p s i s a g o o d i n d i c a t o r t h a t , i n g e n e r a l , t h e i n d i v i d u a l d i f f e r e n c e s w i t h i n t h e a g e g r o u p i n c r e a s e w i t h 67 advancing age up to and i n c l u d i n g the 60 to 69 year age group. For Group 7, however, the spread of the data f o r the group i n d i v i d u a l s i s l e s s pronounced than i t was f o r Group 6. Standard D e v i a t i o n s of the Group Data. The standard d e v i a t i o n s f o r the group data give us a measure of the v a r i a b i l i t y of the data w i t h i n the groups and a l s o an e s t i m a t i o n of how much the d i s t r i b u t i o n of the data i n the d i f f e r e n t groups o v e r l a p s ( r e f e r to F i g u r e 6, a to g ) . In g e n e r a l , the standard d e v i a t i o n s were s m a l l e s t f o r the two youngest groups and they a l s o tended to be s m a l l e r f o r the mid-range wavelengths ( i . e . , green to y e l l o w ) . Trends i n the Peak Values. The peak value f o r the curves showed a s u b s t a n t i a l degree of i n d i v i d u a l v a r i a b i l i t y ( r e f e r to F i g u r e 4, a to g). The peaks ranged from A 537 nm to A 576 nm but there were d i f f e r e n c e s i n the d i s t r i b u t i o n of these peaks i n the d i f f e r e n t age groups. For Group 1 (17 to 20 y e a r s ) , the peak was a t 537 nm for 60% of the s u b j e c t s , a t A 545 f o r 20 % of the s u b j e c t s and at A 560 nm f o r the remaining s u b j e c t . For group 2 (21 to 29 y e a r s ) , the peak was at A 537 nm f o r 71% of the s u b j e c t s and a t A 545 nm f o r the remainder. F i f t y percent of the s u b j e c t s i n Group 3 (30 to 39 years) had a peak value of A 537 nm, 33% had a peak at A 545 nm and the remaining 16% had a peak at A 576 nm. For Group 4 (40 to 49 y e a r s ) , 68 40*. o£ the s u b j e c t s showed a peak value at A 537 nm, and 20% were at each A 545, A 560 and A 576 nm. For Group 5 (50 to 59 y e a r s ) , 57% of the s u b j e c t s had a peak value at A 537 nm and the other 43% had a peak value at 545 nm. S i x t y - s e v e n percent of the s u b j e c t s i n Group 6 (60 to 69 years) showed a peak at A 537 nm, 16% of them had a peak at A 545 nm and one s u b j e c t had a peak that spread from 537 to A 545 nm. F i n a l l y , i n Group 7 (over 70 years) 36% of the s u b j e c t s showed a peak at e i t h e r A 537 nm or A 545 nm, 18% had a peak at A 560 nm and the remaining 9% had a peak at A 576 nm. F l i c k e r versus Color D i s t i n c t i o n During the p i l o t work, i t was n o t i c e d that, while e s t a b l i s h i n g achromatic r e t i n a l t h r e s h o l d s , some s u b j e c t s had d i f f i c u l t i e s d i s t i n g u i s h i n g between the c o l o r and f l i c k e r a t t r i b u t e s of the s t i m u l i and t h a t t h i s l e d to c o n f u s i o n about what was expected of them. This problem was most n o t i c e a b l e i n the blue range of the spectrum; the c o l o r t h r e s h o l d s are s u b s t a n t i a l l y lower than the f l i c k e r t h r e s h o l d s i n t h i s range. This c o l o r / f l i c k e r dichotomy r e q u i r e s that s u b j e c t s are very d i l i g e n t during the t e s t i n g e s p e c i a l l y with the blue s t i m u l i ; they must ensure t h a t they are indeed responding to f l i c k e r and not j u s t to c o l o r . During the t r a i n i n g phase of the achromatic phase of the t e s t i n g , the f l i c k e r / c o l o r d i s t i n c t i o n was drawn to the a t t e n t i o n of the s u b j e c t s and they were i n s t r u c t e d to att e n d s p e c i f i c a l l y to the f l i c k e r even i f they were able to d e t e c t the c o l o r f i r s t . The operator a l s o confirmed with the s u b j e c t the presence of the f l i c k e r i n the stimulus before t e s t i n g commenced for each wavelength. If there were wavelengths for which no f l i c k e r was present at the b r i g h t e s t s t a r t i n g p o i n t , these s t i m u l i were not t e s t e d ( i . e . , f l i c k e r t h r e s h o l d s c o u l d not be a t t a i n e d ) . I t was a l s o decided that the achromatic phase of the t e s t i n g should be completed f i r s t i n order to reduce the c o n f u s i o n between the requirements for the two procedures. These measures seemed to reduce t h i s problem. I t was p o s s i b l e to examine t h i s c o l o r / f l i c k e r d i s t i n c t i o n more c l o s e l y by a s k i n g some s u b j e c t s to r e p o r t both t h r e s h o l d s w i t h i n the achromatic t e s t i n g c o n d i t i o n s ; they were asked to r e p o r t when they could f i r s t d e t e c t the c o l o r and then when they could d e t e c t the f l i c k e r . I t can be seen i n F i g u r e 7 that the c o l o r t h r e s h o l d s are indeed lower than the f l i c k e r t h r e s h o l d s . A l s o , as mentioned e a r l i e r , many of the older observers were unable to d e t e c t the f l i c k e r f o r the extreme short-wavelength s t i m u l i but they were s t i l l able to d e t e c t the c o l o r f o r these s t i m u l i . F i g u r e 8 i l l u s t r a t e s these c o l o r t h r e s h o l d s w i t h i n the achromatic t e s t i n g c o n d i t i o n s f o r two s u b j e c t s . It can be seen t h a t i n the blue wavelength range of the spectrum for these s u b j e c t s , the r e t i n a l t h r e s h o l d s d i v e r g e . At the extreme s h o r t wavelength end of the spectrum the c o l o r t h r e s h o l d s can be seen as an upturn i n the graph. The 70 Figure 7. Separation of color and f l i c k e r thresholds under achromatic testing conditions for 75 year old male subject. i n 5°. O O ) O i n o _ ~T 650.0 400.0 I 450.0 r i 500.0 550.0 WAVELENGTH 600. (NM) i n o o ' C 3 O i n I 650.0 400.0 - 1 450.0 — 1 1 500.0 550.0 WAVELENGTH 600.0 (NM) F i g u r e 8 . Separation of c o l o r and f l i c k e r t h r e s h o l d s under achromatic t e s t i n g c o n d i t i o n s f o r the extreme s h o r t wavelength s t i m u l i . 72 f l i c k e r c o u l d not be c l e a r l y detected by these s u b j e c t s i n t h i s range so they were asked to respond when they could f i r s t d e t e c t the c o l o r of the stimulus. These c o l o r t h r e s h o l d s are c l e a r l y lower than the f l i c k e r t h r e s h o l d s for the wavelengths j u s t proximal to t h i s range and they continue to i n c r e a s e out to the f a r t h e s t blue s t i m u l i ( i . e . , 420 nm). Chromatic Data G r a p h i c a l A n a l y s i s Graphs of Group Average Data. The curves of the averaged group data f o r the chromatic r e t i n a l t h r e s h o l d s show three peaks that roughly c o i n c i d e to short ( b l u e ) , middle (green) and long (red) wavelength energies ( r e f e r to F i g u r e 9). A l l groups had a peak at A 436 nm, another peak at A 521 or A 545 nm and a t h i r d peak at e i t h e r A 611 or A 622 nm. There was a gradual increase i n r e t i n a l t h r e s h o l d s ( i . e . , a decrease i n s e n s i t i v i t y ) f o r the chromatic f u n c t i o n with advancing age. Group 2 had the lowest average r e t i n a l t h r e s h o l d s ( i . e . , h i g h e s t s e n s i t i v i t y ) a c r o s s the e n t i r e spectrum and t h i s data w i l l be used as the b a s i s f o r comparison with the other groups. With the ex c e p t i o n of Group 2, the t h r e s h o l d s f o r the other age groups i n c r e a s e d s e q u e n t i a l l y o v e r a l l with age. In g e n e r a l , the i n c r e a s e s ( i . e . , l o s s i n s e n s i t i v i t y ) are g r e a t e s t i n the blue range. The g r e a t e s t l o s s was a t A 420 nm; a t that p o i n t , Group 7 showed about a 1 l o g u n i t 73 o in o oo" in CD' d (— CD O _ l i n m o. i i i r 1 400.0 450.0 500.0 550.0 600.0 650.0 WRVELENGTH (NM) 700.0 Fig u r e 9 . Data d i s t r i b u t i o n f o r group average data f o r chromatic r e t i n a l increment t h r e s h o l d s . i n c r e a s e i n the average r e t i n a l t h r e s h o l d s with r e s p e c t to Group 2. The increases the blue range ( A 420 to A 487 nm) were a l l over 0.7 l o g u n i t s f o r Group 7. In g e n e r a l , the l o s s e s i n the green range were s l i g h t l y l a r g e r than those i n the red range e s p e c i a l l y f o r the o l d e r groups. For Group 7 (with respect to Group 2), t h i s represents a 0.65 l o g u n i t l o s s at A 521 nm, a 0.45 l o g u n i t l o s s at A 545 nm, a 0.52 log u n i t l o s s at A 611 nm and a 0.53 log u n i t l o s s at A 651 nm. The g r e a t e s t o v e r a l l chromatic peaks were 8.726 l o g u n i t s at A 436 nm, 7.824 lo g u n i t s at A 545 nm and 8.112 l o g u n i t s at A 601 nm. T h i s data was obtained for a 77 year o l d female. The h i g h e s t p o i n t s were at A 420 nm (9.318 l o g u n i t s ) and A 651 nm (8.831 log u n i t s ) which r e p r e s e n t s an approximately 0.5 l o g u n i t d i f f e r e n c e between the extreme blue and red wavelengths. This data was obtained f o r an 81 year o l d female s u b j e c t . This was the same s u b j e c t who had the h i g h e s t o v e r a l l achromatic t h r e s h o l d s . The lowest chromatic r e t i n a l t h r e s h o l d s were: 7.412 l o g u n i t s at A 436 nm f o r a 22 year o l d female s u b j e c t , 7.233 log u n i t s at A 521 nm for a 22 year o l d male s u b j e c t and 7.177 log u n i t s at A 611 nm. The d i f f e r e n c e between the extreme peak values represent a 1.31 l o g u n i t l o s s at A 436 nm, 0.59 l o g u n i t l o s s at the green peak and a 0.95 l o g u n i t l o s s at the red peak. 75 D i s t r i b u t i o n of the Data w i t h i n each Group. In g e n e r a l , the spread of the data w i t h i n the groups f o l l o w e d a s i m i l a r p a t t e r n to that of the achromatic data; the spread i n c r e a s e d with advancing age ( r e f e r to Figure 10, a to g ) . With the chromatic data, however, the spread d i d not decrease f o r the o l d e s t group as i t had with the achromatic d a t a . Achromatic and Chromatic Data  S t a t i s t i c a l A n a l y s i s C o r r e l a t i o n c o e f f i c i e n t s were c a l c u l a t e d for age, sex and wavelength (16 wavelengths; A 487 nm to A 651 nm f o r achromatic and A 420 nm to A 651 nm for c h r o m a t i c ) . C o r r e l a t i o n s were a l s o run f o r age and sex with three c o l o r ranges, blue, green and r e d . These ranges were c a l c u l a t e d as an average of three f i l t e r s i n each of these ranges. The c o r r e l a t i o n s for sex and wavelength and sex and c o l o r range were found to have some e f f e c t at a few of the longer wavelengths; females were found to show s l i g h t l y g r e a t e r l o s s e s f o r some of the long wavelength energies than the males. None of the other c o r r e l a t i o n s for sex were s i g n i f i c a n t . Because of the few s i g n i f i c a n t c o r r e l a t i o n s f o r sex, the remaining c o r r e l a t i o n s were r e c a l c u l a t e d with sex p a r t i a l l e d out. A l l of these c o r r e l a t i o n s were found to be s i g n i f i c a n t at the p_= 0.001 s i g n i f i c a n c e l e v e l . A graph of age c o r r e l a t i o n versus wavelength ( r e f e r to F i g u r e 11) f o r both achromatic and chromatic data i n d i c a t e d t hat the Figure 10 (a - g). Data d i s t r i b u t i o n w i t h i n each i n d i v i d u a l age group for chromatic r e t i n a l increment t h r e s h o l d s . LL 2L m 1 1 1 1 I I 400 .0 450 .0 500.0 550.0 600 .0 650.0 700 WRVELENGTH (NM) F i g u r e l O g . G r o u p V I I c o r r e l a t i o n for age with wavelength i s stronger i n the s h o r t wavelength range, intermediate i n the middle wavelength range and the l e a s t i n the long wavelength range. T h i s r e l a t i o n s h i p i s even c l e a r e r i n the graph of age c o r r e l a t i o n versus c o l o r range ( i . e . , b l ue, green, red) ( r e f e r to Figure 12). In order to examine these a g e - r e l a t e d trends more c l o s e l y , the age with wavelength c o r r e l a t i o n s were analyzed s t a t i s t i c a l l y with a c u r v e - f i t t i n g program. The c o r r e l a t i o n c o e f f i c i e n t s were used and the c o e f f i c i e n t s of d e t e r m i n a t i o n for both the achromatic and chromatic data were c a l c u l a t e d ( r 2 (achromatic)= 0.43 , r 2 (chromatic)= 0.49). T h i s supports the s u p p o s i t i o n t h a t the r e l a t i o n s h i p f o r age with i n c r e a s e s i n r e t i n a l t h r e s h o l d s ( i . e . , l o s s e s i n s e n s i t i v i t y ) i s stronger i n the s h o r t wavelength range, intermediate i n the middle wavelength range and the l e a s t i n the long wavelength range. EXPERIMENT II In g e n e r a l , i t was found that the a g e - s i m u l a t i o n p r e r e c e p t o r a l f i l t e r s had no s u b s t a n t i a l e f f e c t on e i t h e r the achromatic or the chromatic r e t i n a l t h r e s h o l d values except i n the short wavelength range of the spectrum. The data f o r each of the f i l t e r c o n d i t i o n s i s presented i n c o n j u n c t i o n with i t s concomitant b a s e l i n e . A complete set of data f o r a l l c o n d i t i o n s i s i n c l u d e d f o r Subject 2 f o r i l l u s t r a t i v e purposes. Only the data f o r C o n d i t i o n s 3 and 4 Figure 11. Age correlations with wavelength across the v i s i b l e spectrum. are included for the other two subjects; these were the conditions for which there were some interesting findings. Achromatic Data Graphical Analysis It i s apparent that with Conditions 1, 2 and 5 the differences between the f i l t e r conditions and their baselines are a l l within the range of the experimental error bars with minor exceptions (refer to Figure 13, a to j ) . However, for Conditions 3 and 4, there is a d e f i n i t e separation between the data for the f i l t e r conditions and the data for the baseline in the short wavelength range of the spectrum; the difference between the experimental and control conditions in the blue range of the spectrum is greater than experimental error. In Condition 3 ( i . e . , with 3 prereceptoral f i l t e r s ) , the separation begins at A 441 or A 456 nm. In Condition 4 ( i . e . , 4 prereceptoral f i l t e r s ) , the separation begins between A 456 and A 487 nm. It is interesting to note that Subjects 1 and 2 were unable to detect the f l i c k e r for the extreme short wavelength stimuli ( i . e . , beyond A 456 nm for Si and beyond A 436 nm for S2) under Condition 4. As mentioned previously, many of the older subjects were also unable to detect the f l i c k e r in the stimuli in thi s range of the spectrum. A neutral density f i l t e r nonselectively reduces the amount of ambient l i g h t passing through i t . The neutral density f i l t e r for Condition 5 was chosen because i t had in oo' OCT) o o F i g u r e 13 (a - j ) . Achromatic r e t i n a l increment t h r e s h o l d s for Experiment I I . A l l f i l t e r c o n d i t i o n s are i n c l u d e d f o r Subject 2. C o n d i t i o n s 3 and 4 are i n c l u d e d for the other two s u b j e c t s . in oi' I 1 1 I I 400.0 450.0 500.0 550.0 600.0 650.0 WAVELENGTH (NM) F i g u r e 13a. C o n d i t i o n 0 f o r Subject 2. Baseline i I 1 I 400.0 450.0 500.0 550.0 600.0 WAVELENGTH (NM) 650.0 F i g u r e 13b. C o n d i t i o n 5 f o r Subject 2, 00 -Ft 1 1 1 1 1 400.0 450.0 500.0 550.0 600.0 650.0 WAVELENGTH (NM) F i g u r e 13d. C o n d i t i o n 2 f o r Subject 2 00 ui Figure 131. Condition 3 for Subject 3. Figure 13j. Condition 4 for Subject 3. 89 transmissivity c h a r a c t e r i s t i c s ( i . e . , Y%) that were mid-way between those of Condition 3 and 4 (refer to Figure 3); this neutral density f i l t e r was expected to reduce the amount of ambient l i g h t reaching the eye by an amount similar to that of the f i l t e r s in Conditions 3 and 4. Upon examining the data for Condition 5, i t is apparent that the e f f e c t of the neutral density f i l t e r was equivalent across the entire spectrum and that a l l of the losses are within the range of experimental error. This pattern is unlike the one that was established with Conditions 3 and 4. It i s , however, what would be expected for a neutral density f i l t e r Furthermore, i t i l l u s t r a t e s that the reduction in overall luminance is not s u f f i c i e n t to explain the results obtained for Conditions 3 and 4. Chromatic Data Graphical Analysis It was apparent that with Conditions 1, 2 and 5 the differences between the f i l t e r conditions and their baselines were a l l within the range of the experimental error bars with minor exceptions. For Conditions 3 and 4, there was more of a separation between the data for the f i l t e r conditions and the data for the baseline conditions in the short wavelength range of the spectrum. The separation, however, was not as dramatic as with the achromatic procedure; for much of the data, the separation was within or close to within the error bars. A clear 90 separation between the f i l t e r c o n d i t i o n s ( I . e . , c o n d i t i o n s 3 & 4) was found only for Subject 3 ( r e f e r to Figure 14 a to g). Discussion In general, i t was found that there i s a gradual increase i n both achromatic and chromatic r e t i n a l thresholds ( i . e . , a decrease In s e n s i t i v i t y ) with advancing age. As expected, t h i s l o s s ( i . e . , increase i n r e t i n a l thresholds) was the l a r g e s t i n the short wavelength range of the spectrum. However, the losses were intermediate i n the middle wavelength range of the spectrum and l e a s t i n the long wavelength end of the spectrum. I t had been expected that the losses i n the long wavelength range of the spectrum would be somewhat l a r g e r than those i n the middle wavelength range. This had been found by other researchers who had examined the e f f e c t s of advancing age on r e t i n a l thresholds (see for example, V e r r i e s t & I s r a e l , 1965; V e r r i e s t , 1970; V e r r i e s t & U v i j l s , 1977). A p o s s i b l e explanation for t h i s d i f f e r e n c e i s the adaptation f i e l d s used for these various s t u d i e s . The present study was completed under high photopic c o n d i t i o n s ( i . e . , 200 cd m - 2) w h e r e a s the aforementioned s t u d i e s by V e r r i e s t and h i s colleagues were completed under high mesopic c o n d i t i o n s (e.g., 10 cd m - 2). This p o s s i b i l i t y could be explored e m p i r i c a l l y ; t e s t i n g could be conducted on the same subjects using the d i f f e r e n t adaptation f i e l d s . Figure 14 (a - j ) . Chromatic r e t i n a l increment thresholds for Experiment II. A l l f i l t e r conditions are included for Subject 1. Conditions 3 and 4 are included for the other two subjects. o CO in cd' 5 ° . OO) CD O in en' in CO 5 ° . OCT) CO o _J in eri" 1 1 1 1 — T 1 400.0 450.0 500.0 550.0 600.0 650.0 700.0 WAVELENGTH (NM) Figure 14a. Condition 0 for Subject 2. 400.0 i 450.0 500.0 550.0 600.0 WAVELENGTH (NM) —i 650.0 CO Figure 14b. Condition 5 for Subject 2." 96 Data D i s t r i b u t i o n G e n e r a l l y , the d i s t r i b u t i o n of the data w i t h i n the groups became more symmetrical across the spectrum and more d i s p e r s e d between the s u b j e c t s f o r each group with advancing age. T h i s trend, however, began to taper o f f f o r the o l d e s t group of s u b j e c t s . There were 3 p o i n t s about the data d i s t r i b u t i o n t h at should be examined. For the youngest two groups, the d i s t r i b u t i o n was n o t i c e a b l y asymmetrical. The spread of the data f o r the sh o r t wavelength e n e r g i e s was much greater than i t was f o r the long wavelength e n e r g i e s ; the data at the red end of the spectrum was more homogeneous than the data a t the blue end. It i s not reasonable to speculate on the causes of t h i s d i f f e r e n c e w i t h i n the framework of t h i s study but s e v e r a l p l a u s i b l e e x p l a n a t i o n s may be con s i d e r e d . The v a r i a b i l i t y at the short wavelength end of the spectrum i n the young s u b j e c t s could be a r e f l e c t i o n of: (1) d i f f e r e n c e s i n the d i s t r i b u t i o n of blue cone r e c e p t o r s i n the r e t i n a (2) d i f f e r e n c e s i n the pigmentation of the macula l u t e a . I t i s known t h a t there 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 the amount of pigmentation i n the macula l u t e a . Heavier pigmentation would absorb more of the blue energy (see f o r example, Lakowski, 1962) and thus decrease s e n s i t i v i t y to the blue s t i m u l i . (3) c o n f u s i o n about the d i s t i n c t i o n between the c o l o r and f l i c k e r a t t r i b u t e s of the t a r g e t s t i m u l u s . T h i s problem 97 is part icularly prevalent for the short wavelength stimuli (refer to discussion of this problem in Methodological Issues below). It is possible that inconsistencies In subjects c r i t e r i a for responding to the blue stimuli may have v a c i l l a t e d between these two parameters. This could have increased the v a r i a b i l i t y in the thresholds for the blue stimuli e s p e c i a l l y those at the extreme short wavelength end of the spectrum. A l l of these p o s s i b i l i t i e s could a l l be explored experimentally. With Group 3, the d i s t r i b u t i o n was markedly d i f f e r e n t from the pattern of the other groups because there was one subject that produced data which was incongruous with the remainder of the group. It was also not similar to the general trends across the groups. This o u t l i e r data was for a 32 year old female subject. Nothing unusual was noticed about her during the testing session. In addition, a post-hoc examination of her subject health history questionnaire revealed l i t t l e except that she is a smoker. Smokers were not common in thi s sample esp e c i a l l y among the young subjects. It i s , however, not possible to draw any conclusions about the causes for t h i s subjects divergent data and i t is feasible that this data is a true expression of the range of r e t i n a l thresholds for this age group. It was found that the data for the oldest group ( i . e . , Group 7) showed less v a r i a b i l i t y across the entire spectrum than the next oldest group (Group 6 ) . In addition, the pattern for the d i s t r i b u t i o n of the data was somewhat 9 8 d i f f e r e n t than for the other groups which had shown e i t h e r a g r e a t e r spread i n the short wavelength range than i n the long wavelength range or a f a i r l y symmetrical d i s t r i b u t i o n a c r o s s the whole spectrum. The data f o r Group 7, however, d i s p l a y e d a greater spread f o r the data at the long wavelength end i n comparison to the data at the short wavelength end of the spectrum. The reason f o r t h i s change i n the general trend f o r the o l d e s t group of s u b j e c t s i s u n c l e a r . I t i s ,however, q u i t e p o s s i b l e that these s u b j e c t s ( i . e . , Group 7) were not r e p r e s e n t a t i v e f o r t h e i r age group (see d i s c u s s i o n of t h i s under Sample S e l e c t i o n , Normal Aging P o p u l a t i o n ) . Methodological Issues  F l i c k e r / C o l o r D i s t i n c t i o n I t was n o t i c e d while e s t a b l i s h i n g the achromatic r e t i n a l 'thresholds, that some s u b j e c t s were confused by the d i f f e r e n c e between the c o l o r and f l i c k e r a t t r i b u t e s of the s t i m u l i . This l e d to some problems f o r the s u b j e c t s with r e s p e c t to d e c i d i n g to which a t t r i b u t e they were to respond. The problem was addressed by m o d i f i c a t i o n s i n the t e s t i n g procedure (as d i s c u s s e d i n the r e s u l t s s e c t i o n ) . The c o l o r f l i c k e r dichotomy i s most n o t i c e a b l e i n the blue range of the spectrum where there i s l e s s energy a v a i l a b l e ( i . e . , V c u r v e ) . I t was found that some of the s u b j e c t s , e s p e c i a l l y the o l d e r ones, had d i f f i c u l t i e s d e t e c t i n g the f l i c k e r i n the extreme shor t wavelength s t i m u l i even though they could 99 s t i l l d e t e c t t h e c o l o r ( r e f e r t o F i g u r e 8 ) . The c o l o r t h r e s h o l d s i n t h e s h o r t w a v e l e n g t h r a n g e a p p e a r i n t h i s g r a p h a s a n u p t u r n a t t h e e x t r e m e b l u e e n d o f t h e c u r v e . T h e s e c o l o r t h r e s h o l d s a r e c l e a r l y l o w e r t h a n t h e f l i c k e r t h r e s h o l d s j u s t p r o x i m a l t o t h i s p o i n t . T h e y a l s o c o n t i n u e t o d e c r e a s e ( i . e . , move t o w a r d s l o w e r r e t i n a l t h r e s h o l d s ) t o w a r d t h e e x t r e m e s h o r t w a v e l e n g t h s t i m u l i . T h i s may be a n i n d i c a t i o n t h a t i n i t i a l l y ( i . e . , t e s t i n g p r o c e e d s f r o m p r o x i m a l t o d i s t a l a t t h e b l u e e n d ) t h e s u b j e c t s may s t i l l be r e s p o n d i n g p a r t i a l l y t o a f a i n t f l i c k e r a n d , t h e r e f o r e t h e s e t h r e s h o l d s w o u l d be e x p e c t e d t o be s i i g h t l y ' h i g h e r t h a n when t h e s u b j e c t i s r e s p o n d i n g s t r i c t l y t o c o l o r . F u r t h e r m o r e , a s m e n t i o n e d w i t h r e s p e c t t o t h e y o u n g s u b j e c t s , t h e y may be v a c i l l a t e d b e t w e e n t h e c o l o r a n d f l i c k e r q u a l i t i e s a s t h e i r c r i t e r i a f o r r e s p o n d i n g . I t s e e m s t h a t t h i s v a c i l l a t i o n w o u l d be m o s t l i k e l y t o o c c u r c l o s e t o t h e p o i n t w h e r e t h e f l i c k e r b e g i n s t o f a l l b e l o w t h e t h r e s h o l d p o i n t . A t t h a t p o i n t , t h e s u b j e c t h a s l e s s i n f o r m a t i o n o n w h i c h t o b a s e t h e i r d e c i s i o n . T h e r e a r e s e v e r a l p o s s i b l e e x p l a n a t i o n s f o r t h i s c o l o r / f l i c k e r c o n f u s i o n p h e n o m e n o n d u r i n g a c h r o m a t i c t e s t i n g . F i r s t l y , w i t h t h e h i g h p h o t o p i c l u m i n a n c e b a c k g r o u n d , t h e a c h r o m a t i c s y s t e m i s s u p p r e s s e d w i t h r e s p e c t t o t h e c h r o m a t i c o n e . I n t h e d i c h o t o m y t h a t e x i s t s b e t w e e n t h e a c h r o m a t i c a n d c h r o m a t i c s y s t e m s , a h i g h l y p h o t o p i c a d a p t a t i o n f i e l d i s one o f t h e f a c t o r s t h a t h a s b e e n f o u n d t o s e l e c t i v e l y s u p p r e s s t h e a c h r o m a t i c s y s t e m w i t h r e s p e c t 100 to the chromatic system. The f a c t t h a t higher c o l o r t h r e s h o l d s were found d u r i n g the achromatic t e s t i n g i s i n keeping with t h i s s u p p o s i t i o n . Secondly, i t was noted that the c o l o r / f l i c k e r c o n f u s i o n may be i n f l u e n c e d by p e r s o n a l i t y v a r i a b l e s . The procedure for t e s t i n g r e t i n a l t h r e s h o l d s i s v e r y demanding and i t r e q u i r e s c o o p e r a t i o n and perseverance on the part of the s u b j e c t . Subjects who have more d i f f i c u l t f o c u s i n g on the task at hand may have more t r o u b l e r e s o l v i n g the c o l o r / f l i c k e r c o n f u s i o n . G e n e r a l l y , i t was found that the younger s u b j e c t s were l e s s a t t e n t i v e and more impatient d u r i n g t e s t i n g . Many of the young s u b j e c t s were noted to become a g i t a t e d , and f i d g e t y during the extended t e s t i n g and o f t e n i t was d i f f i c u l t y to maintain t h e i r a t t e n t i o n . The o l d e r s u b j e c t s were g e n e r a l l y more d i l i g e n t and focused d u r i n g the t e s t i n g . A f i n a l c o n s i d e r a t i o n i s t h a t with the older s u b j e c t s , the c o l o r / f l i c k e r c o n f u s i o n probably r e s u l t s from l o s s e s i n s e n s i t i v i t y and/or reduced f l i c k e r f u s i o n r a t e s . Because the s t i m u l i may be w e l l below t h e i r f l i c k e r t h r e s h o l d , u n i n i t i a t e d s u b j e c t s may respond when they d e t e c t the c o l o r of the stimulus because there i s no other i n f o r m a t i o n a v a i l a b l e to them. This may e x p l a i n why some olde r s u b j e c t s have lowered r e t i n a l t h r e s h o l d s for the extreme s h o r t wavelength s t i m u l i . I t was found t h a t although s u b j e c t s were i n s t r u c t e d on t h i s dilemma some of the data had a s l i g h t upturn at the extreme blue end. T h i s was p a r t i c u l a r l y p r e v a l e n t f o r the o l d e r s u b j e c t s and a c t u a l l y the graph of the group averaged data has an obvious 101 upturn f o r the b l u e e n d point ( i . e . , A 472 nm i n this c a s e ) . The i s s u e o f a n a p p r o p r i a t e f l i c k e r r a t e f o r a c h r o m a t i c t e s t i n g w i t h e l d e r l y s u b j e c t s i s y e t t o be r e s o l v e d . A f l i c k e r r a t e o f 24 Hz i s c u s t o m a r i l y u s e d f o r e s t a b l i s h i n g a c h r o m a t i c r e t i n a l t h r e s h o l d s . T h i s f l i c k e r r a t e , h o w e v e r , was c h o s e n a s a r e s u l t o f w o r k d o n e o n c o l l e g e age s u b j e c t s . T h e r e i s e v i d e n c e , t h o u g h , t h a t t h i s f l i c k e r r a t e may n o t be a p p r o p r i a t e f o r e l d e r l y o b s e r v e r s ( f o r e x a m p l e , T y l e r , 1 9 8 9 ) . D e L a n g e ( 1 9 5 3 ) was t h e f i r s t t o s u g g e s t t h a t a l o w e r f l i c k e r r a t e ( i . e . , 10 H z ) w o u l d be more a p p r o p r i a t e f o r a g e d s u b j e c t s b e c a u s e o f a n a g e - r e l a t e d d e c l i n e i n t h e c r i t i c a l f l i c k e r f u s i o n r a t e . T h i s , h o w e v e r , h a s n o t t h u s f a r b e e n t a k e n i n t o c o n s i d e r a t i o n i n a g i n g s t u d i e s . I t w o u l d be i m p e r a t i v e t h a t t h e f l i c k e r r a t e be c o n s i d e r e d a s a n e x p e r i m e n t a l p a r a m e t e r i n f u t u r e s t u d i e s o f a g e - r e l a t e d c h a n g e s i n a c h r o m a t i c r e t i n a l t h r e s h o l d s . F o r a more d e t a i l e d d i s c u s s i o n o f t h i s p r o b l e m , r e f e r t o t h e r e c e n t p a p e r b y L a k o w s k i a n d h i s c o l l e a g u e s ( 1 9 9 0 ) . A t t e n t i o n F a c t o r s T h i s m e t h o d o f a s s e s s m e n t i s g e n e r a l l y more t i m e c o n s u m i n g a n d d e m a n d i n g t h a n t h e s t a n d a r d f o r m s o f c o l o r v i s i o n a n a l y s i s . P a t i e n t a l e r t n e s s a n d c o o p e r a t i o n p l a y a l a r g e r o l e i n t h e o v e r a l l s u c c e s s o f t h e r e s u l t s ( i . e . , s e n s i t i v i t y a n d a c c u r a c y ) . I t was f o u n d t h a t f o r b o t h t h e a c h r o m a t i c a n d c h r o m a t i c 102 p r o c e d u r e s , the youngest group (17 t o 20 year o l d s ) had s l i g h t l y h i g h e r t h r e s h o l d s than the next group (21 t o 29 year o l d s ) . T h i s d i f f e r e n c e was c o n s i s t e n t a c r o s s the spectrum but i t was c e r t a i n l y w i t h i n the range of the s t a n d a r d d e v i a t i o n s f o r the d a t a . A p o s s i b l e e x p l a n a t i o n f o r the s l i g h t l y h i g h e r s e n s i t i v i t y of Group 2 may have been a t t e n t i o n a l f a c t o r s . I t was n o t i c e d d u r i n g the t e s t i n g s e s s i o n s t h a t the youngest s u b j e c t s had the g r e a t e s t d i f f i c u l t y f o c u s i n g t h e i r a t t e n t i o n on the t a s k . They o f t e n became f r u s t r a t e d and r e q u e s t e d more r e s t b reaks than any o t h e r group. I t i s p o s s i b l e t h a t t h e i r i n c o n s i s t e n t a t t e n t i o n a l p a t t e r n s may have had a s l i g h t l y d e t r i m e n t a l e f f e c t on t h e i r r e t i n a l t h r e s h o l d s w i t h r e s p e c t to the more a t t e n t i v e s u b j e c t s i n Group 2. Sample S e l e c t i o n Sex D i f f e r e n c e s . The p r i m a r y weakness w i t h r e s p e c t t o g e n e r a l i z a b i l i t y of these f i n d i n g s was the l i m i t e d number of male (n(male) = 19, N = 47) s u b j e c t s who p a r t i c i p a t e d i n the s t u d y . The f i n d i n g s of the p r e s e n t r e s u l t s would be s t r e n g t h e n e d i f the sample of males f o r each age group ( w i t h the e x c e p t i o n of Group 3) c o u l d be expanded so t h a t i t was e q u i v a l e n t t o the sample of females. There were some c o r r e l a t i o n s t h a t were s u g g e s t i v e of a sex d i f f e r e n c e i n the l o n g wavelength range of the spectrum; t h e y i n d i c a t e d t h a t the female s u b j e c t s showed g r e a t e r l o s s e s f o r some of the l o n g wavelength s t i m u l i than the male s u b j e c t s . 103 U n f o r t u n a t e l y , b e c a u s e t h e o l d e s t s u b j e c t s w e r e p r e d o m i n a n t l y f e m a l e ( G r o u p 7 ; n ( f e m a l e ) = 8 , n ( m a l e ) = 3 ) , i t i s p o s s i b l e t h a t t h i s e f f e c t i s p r i m a r i l y a r e f l e c t i o n o f t h i s d i s p a r i t y ( i . e . , t h e o l d e s t s u b j e c t s w e r e m a i n l y f e m a l e - a l l s u b j e c t s o v e r 80 y e a r s w e r e f e m a l e ) . N o r m a l A g i n g P o p u l a t i o n . F o r t h e p u r p o s e s o f t h i s s t u d y , we w e r e i n t e r e s t e d i n e x a m i n i n g t h e c h a n g e s i n c o l o r v i s u a l f u n c t i o n ( i . e . , a c h r o m a t i c a n d c h r o m a t i c r e t i n a l t h r e s h o l d s ) w i t h i n t h e n o r m a l a g i n g p o p u l a t i o n . N o r m a l c y , t h e r e f o r e , was d e f i n e d w i t h r e s p e c t t o t h e a b s e n c e o f a n y k n o w n p a t h o l o g i c a l c o n d i t i o n , o c u l a r ( e . g . , c a t a r a c t s ) o r s y s t e m i c ( e . g . , d i a b e t e s m e l l i t u s ) , t h a t i s k n o w n t o d i r e c t l y e f f e c t v i s u a l p e r f o r m a n c e . T h i s was d o n e s o t h a t a n y c h a n g e s i n v i s u a l f u n c t i o n t h a t w e r e f o u n d c o u l d be more c o n f i d e n t l y a s c r i b e d t o a n o n - d i s e a s e - r e l a t e d a g i n g p r o c e s s ( i . e . , a n a l t e r a t i o n t h a t i s w i t h i n t h e n o r m a l r a n g e o f a g i n g c h a n g e i n t h e v i s u a l s y s t e m ) . A l t h o u g h t h e s u b j e c t s i n t h i s s t u d y q u a l i f i e d a s n o r m a l a g e d s u b j e c t s , i t i s p o s s i b l e t h a t t h e y w e r e n o t r e p r e s e n t a t i v e o f t h e i r a g e g r o u p w i t h i n t h e g e n e r a l p o p u l a t i o n . S u b j e c t s i n t h e o l d e r a g e g r o u p s ( p a r t i c u l a r l y s u b j e c t s o v e r 70 y e a r s o f a g e ) w e r e r e c r u i t e d t h r o u g h l o c a l s e n i o r s ' c e n t e r s . P a r t i c i p a n t s a t t h e s e c e n t e r s a r e l i k e l y t o r e p r e s e n t t h e u p p e r r a n g e o f p e o p l e o f t h e i r a g e f o r h e a l t h a n d a c t i v i t y l e v e l . I n a d d i t i o n , i n o r d e r t o p a r t i c i p a t e i n t h i s s t u d y , t h e s u b j e c t s w e r e r e q u i r e d t o 104 t r a n s p o r t t h e m s e l v e s t o t h e u n i v e r s i t y . We c a n p o s t u l a t e t h a t p e o p l e who w e r e w i l l i n g a n d a b l e t o do t h i s w e r e r e a s o n a b l y h e a l t h y a n d m o b i l e . T h i s s e l f - s e l e c t i o n f a c t o r w i t h t h e o l d e r s u b j e c t s may h a v e r e s u l t e d i n a n o l d e r g r o u p t h a t r e p r e s e n t s t h e u p p e r ( i . e . , t h e b e s t f o r t h e i r a g e ) r a n g e o f p e o p l e o f t h a t a g e . I t w o u l d h a v e b e e n v a l u a b l e t o be a b l e t o e x t e n d t h i s s t u d y t o i n c l u d e a w i d e r r a n g e o f p e o p l e i n t h e g r o u p o f s u b j e c t s o v e r 70 y e a r s o f a g e ( e . g . , c o n v a l e s c i n g , a n d h o m e b o u n d p e o p l e ) . B e c a u s e o f t h e d e m a n d s o f t h e t a s k a n d t h e n a t u r e o f t h e e q u i p m e n t , h o w e v e r , t h i s w o u l d be p r o h i b i t i v e l y d i f f i c u l t t o a c c o m p l i s h . F u r t h e r m o r e , t h e i s s u e o f w h i c h p e o p l e c o n s t i t u t e t h e n o r m a l r a n g e o f d i f f e r e n c e w i t h i n a n y a g e g r o u p i s o f t e n v e r y d i f f i c u l t t o c l e a r l y d e f i n e . B y u s i n g o u r c r i t e r i a o f n o r m a l ( a s d e f i n e d e a r l i e r ) a n d t a k i n g i n t o c o n s i d e r a t i o n t h e s e l f - s e l e c t i o n f a c t o r , i t i s p r o b a b l y a s o u n d a s s u m p t i o n t h a t t h e o l d e r s a m p l e i n c l u d e i n t h i s s t u d y r e p r e s e n t s t h e v e r y b e s t f u n c t i o n a l l e v e l f o r t h e i r age g r o u p . R o l e o f P r e r e c e p t o r a l F a c t o r s The d a t a f r o m E x p e r i m e n t I I i s s u g g e s t i v e . I n g e n e r a l , t h e r e s u l t s o f t h i s s t u d y s u p p o r t t h e p o s t u l a t e t h a t p r e r e c e p t o r a l f a c t o r s p l a y a r o l e i n t h e a g e - r e l a t e d c h a n g e s t h a t a r e f o u n d w i t h c o l o r v i s i o n f u n c t i o n e s p e c i a l l y i n t h e s h o r t w a v e l e n g t h r a n g e o f t h e s p e c t r u m . T h e y do n o t , h o w e v e r , a c c o u n t f o r a l l o f t h e f u n c t i o n a l l o s s e s t h a t a r e s e e n i n a n a g i n g p o p u l a t i o n . The p r e r e c e p t o r a l s i m u l a t i o n 105 f i l t e r s produced l i t t l e to no effect on r e t i n a l t h r e s h o l d s i n the middle and long wavelength ranges of the spectrum. Some e f f e c t s were found f o r the short wavelength range of the spectrum; these e f f e c t s were most pronounced f o r the extreme s h o r t wavelength s t i m u l i . S e v e r a l i n t e r e s t i n g p o i n t s about t h i s data should be noted. With the achromatic data, 2 of the s u b j e c t s could not de t e c t the f l i c k e r f o r the extreme blue s t i m u l i . T h i s i s p a r t i c u l a r l y i n t e r e s t i n g because a s i m i l a r p a t t e r n was found i n Experiment I f o r the normal aging s u b j e c t s . In a d d i t i o n , i t should a l s o be noted that t h i s e f f e c t was most n o t i c e a b l e with Subject 1. T h i s s u b j e c t was the l e a s t s e n s i t i v e but most r e l i a b l e observer; s u b j e c t 1 had the hig h e s t r e t i n a l t h r e s h o l d s but he a l s o gave the most c o n s i s t e n t responses. I t i s , t h e r e f o r e , not s u r p r i s i n g that t h i s s u b j e c t a l s o showed the g r e a t e s t l o s s e s under the age f i l t e r s i m u l a t i o n c o n d i t i o n s . The e f f e c t s . o f the aging s i m u l a t i o n f i l t e r s were much more apparent and c o n s i s t e n t with the achromatic r e t i n a l t h r e s h o l d s than with the chromatic ones. For the chromatic c o n d i t i o n only Subject 3 showed a marked decrease ( i . e . , g r e a t e r than e r r o r ) at the blue end f o r Co n d i t i o n s 3 and 4; fo r the achromatic c o n d i t i o n , a l l of the s u b j e c t s showed l o s s e s g r e a t e r than e r r o r at the blue end of the spectrum. I t i s unclear why t h i s d i f f e r e n c e should e x i s t between the achromatic and chromatic c o n d i t i o n s . I t i s p o s s i b l e that i t was p a r t i a l l y a r e s u l t of the greater i n d i v i d u a l d i f f e r e n c e s 106 i n the chromatic f u n c t i o n s than i n the achromatic f u n c t i o n s ( i . e . , g r e a t e r v a r i a b i l i t y i n peak and d e p r e s s i o n v a l u e s , general shape of the f u n c t i o n e t c . ) . I t would be i n t e r e s t i n g to t r y to address t h i s d i f f e r e n c e using a l a r g e r sample of s u b j e c t s f o r t h i s experiment. 107 R e f e r e n c e s A U l h o m , E . & H a r m s , H . V i s u a l P e r i m e t r y (1972). I n D . J a m e s o n & L . M . H u r v l c h , ( E d s . ) V i s u a l P s y c h o p h y s i c s ,  V o l u m e V I I / 4 . H a n d b o o k o f s e n s o r y p h y s i o l o g y . New Y o r k : S p r i n g e r - V e r l a g . B i r r e n , J . E . & S h a l e , K . w . (1977) . H a n d b o o k o f t h e p s y c h o l o g y o f a g i n g . New Y o r k : V a n N o s t r a n d R e i n h o l d C o m p a n y . B o l c e , M . L . , T i n k e r , M . A . & P a t e r s o n D . G . (1948). C o l o r v i s i o n a n d a g e . A m e r i c a n J o u r n a l o f P s y c h o l o g y , 61, 520-527. B o y t o n , R . M . , I k e d a , M . & S t i l e s , W . S . (1964). V i s i o n  R e s e a r c h , 4, 87. C h a p a n i s A . (1950). R e l a t i o n s h i p s b e t w e e n a g e , v i s u a l a c u i t y a n d c o l o r v i s i o n . Human B i o l o g y : A R e c o r d o f  R e s e a r c h , 22.(1), 1-33. D e L a n g e , H . (1953). R e l a t i o n s h i p b e t w e e n c r i t i c a l f l i c k e r -f r e q u e n c y c h a r a c t e r i s t i c s o f t h e e y e . J o u r n a l o f t h e  O p t i c a l S o c i e t y o f A m e r i c a , 44_( 5 ) , 380-389. D u n n , P . M . (1979) A s t u d y o f g r a d i e n t s a n d s p a t i a l s u m m a t i o n i n t h e r e t i n a b y s t a t i c p e r i m e t r y w i t h  p h o t o m e t r i c a l l y - e q u a t e d s t i m u l i u n d e r f u l l y - p h o t o p i c  a n d f u l l y - s c o t o p i c c o n d i t i o n s . U n p u b l i s h e d m a s t e r ' s t h e s i s , U n i v e r s i t y o f B r i t i s h C o l u m b i a , V a n c o u v e r , B r i t i s h C o l u m b i a . H a e g e r s t r o m - P o r t n o y , G . , H e w l e t t , S . E . & B a r r , S . A . N . (1989) . S c o n e l o s s w i t h a g i n g . I n B . Drum & G . V e r r i e s t ( E d s . ) , C o l o u r v i s i o n d e f i c i e n c i e s I X ( p p . 3 4 5 -352) . The N e t h e r l a n d s : K l u w e r A c a d e m i c P u b l i s h e r s . J o h n s o n , C . A . , A d a m s , A . J . , T w e l k e r , J . D . & Q u i g g , J . M . (1988) . A g e - r e l a t e d c h a n g e s i n t h e c e n t r a l v i s u a l f i e l d f o r s h o r t - w a v e l e n g t h - s e n s i t i v e p a t h w a y s . J o u r n a l o f t h e  O p t i c a l S o c i e t y o f A m e r i c a A , 5, 2131-2139. K i n g - S m i t h , P . E . & C a r d e n , D . (1975) . L u m i n a n c e a n d o p p o n e n t - c o l o r c o n t r i b u t i o n s t o v i s u a l d e t e c t i o n a n d a d a p t a t i o n a n d t o t e m p o r a l a n d s p a t i a l i n t e g r a t i o n . J o u r n a l o f t h e O p t i c a l S o c i e t y o f A m e r i c a , 66.(7), 709-17. L a k o w s k i , R . (1958). Age a n d c o l o u r v i s i o n . The A d v a n c e m e n t o f S c i e n c e , X V ( 5 9 ) , 231-236. 108 Lakowski, R. (1959). Experiments i n colour v i s i o n , e s p e c i a l l y with reference to aging. B u l l e t i n of the  B r i t i s h P s y c h o l o g i c a l S o c i e t y , 38-39. Lakowski, R. (1962). Is d e t e r i o r a t i o n of co l o u r d i s c r i m i n a t i o n with age due to lens or r e t i n a l changes? Die Farbe, l l ( N r . 1/6), 69-86. Lakowski, R. (1969). Theory and p r a c t i c e of c o l o u r v i s i o n t e s t i n g : A review (Part 1). The B r i t i s h J o u r n a l of  I n d u s t r i a l Medicine. 26, 265. Lakowski, R., Wright, W. D., & O l i v e r , K. (1977). A Goldmann perimeter with high luminance chromatic t a r g e t s . Canadian J o u r n a l of Ophthalmology, 12, 203-210. Lakowski,R., Lakowski, R.I. & Hancock, S. (1990). Me t h o d o l o g i c a l issues i n the assessment of achromatic  r e t i n a l t h r e s h o l d s with the B.C.U.P.. In pr e s s . Q u e l l e t t e , L.A. (1953). Age d i f f e r e n c e s i n c o l o r d i s c r i m i n a t i o n . Unpublished master's t h e s i s , Fordham U n i v e r s i t y , New York, New York. Said, F. S. & Weale, R, A. (1959). The v a r i a t i o n with age of the s p e c t r a l t r a n s m i s s i v l t y of the l i v i n g human c r y s t a l l i n e l e n s . G e r o n t o l o g i a , 3, 213-231. Sloan, L.L. (1940). Instruments and t e c h n i c s for the c l i n i c a l t e s t i n g of l i g h t sense. VI. Siz e of p u p i l as a v a r i a b l e f a c t o r on the determination of the l i g h t minimum. Arc h i v e s fo Ophthalmology, 23, 258-274. Smith, H.C. (1943). Age d i f f e r e n c e s i n c o l o r d i s c r i m i n a t i o n . The Jo u r n a l of General Psychology,, 2_9, 191-226. T i f f i n , J . & Kuhn, K.S. (1942). Colour d i s c r i m i n a t i o n i n i n d u s t r y . Archives of Ophthalmology, 28, 851-859. T y l e r , C.W. (1989). Two processes c o n t r o l v a r i a t i o n s i n f l i c k e r s e n s i t i v i t y over the l i f e s p a n . J o u r n a l of the  O p t i c a l S o c i e t y of America, 6(4), 481-490. V e r r i e s t , G. (1964). Further s t u d i e s on ac q u i r e d d e f i c i e n c y of c o l o u r d i s c r i m i n a t i o n . J o u r n a l of the O p t i c a l  S o c i e t y of America, 53, 185-195. V e r r i e s t , G. & Kandemir, H. (1974). Normal s p e c t r a l increment t h r e s h o l d s on a white background. Die Farbe, 23, Nr.1/4, 3-16. V e r r i e s t , G. & U v i j l s , A. (1977). S p e c t r a l increment t h r e s h o l d s on a white background i n d i f f e r e n t age 109 g r o u p s o f n o r m a l s u b j e c t s a n d i n a c q u i r e d o c u l a r d i s e a s e s . D o c u m e n t a O p h t h a l m o l o g i c a , 4_3_( 2 ) , 2 1 7 - 2 4 8 . V e r r i e s t , G . ( 1 9 7 2 ) . The r e l a t i v e s p e c t r a l l u m i n o u s e f f i c i e n c y i n d i f f e r e n t age g r o u p s o f a p h a k i c e y e s . D i e F a r b e , 21_(Nr . 1 / 6 ) , 1 7 - 2 5 . W a l d , G . ( 1 9 4 5 ) . Human v i s i o n a n d t h e s p e c t r u m . S c i e n c e , 1 0 1 ( 2 6 3 5 ) , 6 5 3 - 6 5 8 . W e a l e , R . A . ( 1 9 6 3 ) . The A g e i n g E y e . L o n d o n : H . K . L e w i s & C o . W y s z e c k i , G . & S t i l e s , W . S . ( 1 9 6 7 ) . C o l o r s c i e n c e . New Y o r k : W i l e y . 110 APPENDIX A LIST OF INTERFERENCE FILTERS WAVELENGTH FWHM TYPE OF PEAK (nm) (nm) FILTER % 1* 420.88 8.53 3 40 2* 436.6 11.2 55 3 441.7 10+/-2 3 45 4* 456.7 9.4 59 5* 472.65 9.41 3 45 6* 487.5 11.6 64 7 490.5 10+/-2 3 50 8* 500.9 11 3 57 9 512.05 10.6 3 50 10* 521.5 9.12 3 50 11 537.0 10+/-2 3 50 12* 545.9 10.4 54 13* 560.44 10.88 3 50 14* 576.5 9.2 62 15* 581.1 9.71 3 50 16* 582.65 10+/-2 17 590.0 10+/-2 3 50 18* 601.76 9.41 3 50 19* 611.7 10+/-2 3 50 20* 622.9 11.17 3 50 21* 651.0 11.8 61 ALL 21 INTERFENCE FILTERS WERE USED FOR ACHROMATIC TESTING. THE FILTERS USED FOR CHROMATIC TESTING ARE MARKED WITH AN* 111 Subject Number: Examination Date: NAME: GENDER: male female BIRTHDATE: OCCUPATION: ETHNIC BACKGROUND: HEALTH HISTORY For the f o l l o w i n g s e c t i o n s , please c i r c l e the a p p r o p r i a t e responses. FAMILY HISTORY please i n d i c a t e which of the f o l l o w i n g apply to y o u r f a m i l y C a r d i o v a s c u l a r Problems yes no C a t a r a c t s yes no Colour B l i n d n e s s yes no Diabetes yes no Glaucoma yes no Hypertension yes no Mi g r a i n e s yes no T h y r o i d Problems yes no V i s u a l Problems yes no ( i f yes, please s p e c i f y ) Other yes no ( i f yes, please s p e c i f y ) 112 PERSONAL HISTORY please indicate which of the following apply to you Cardiovascular Problems yes no Cataracts yes no Colour Blindness yes no Diabetes yes no Glaucoma yes no Hypertension yes no Migraines yes no Thyroid Problems yes no Visual Problems ( i f yes, please specify) yes no Extended use of medication yes no (for example, aspirin, oral contraceptives etc.) (i f . y e s , please specify medication, duration and recency of use) Smoked cigarettes yes no ( i f yes, please specify duration, number of packs/day and recency of use) Other ( i f yes, please specify) yes no PROJECT- t r a n s m i s s i o n of a g i n g f a l t e r s SAMPLE : 1 a g i n g f i l t e r ( w h i te s t a n d a r d ) 113 APPENDIX C LABELS 1 1 Jum 0'b.s SmpJ Src A 2d A a C 2d C o 065 2d D d A) .93.60 C) 80 .93 D.) 78. 5J y 33. S7 B?. 54 32. S2 Z 26. 43 86. 67 73. 92 x y A) 0.*5975 0. 4J 046 O D.32363 D.32991 D.) 0. 326J 2 0. 342.34 DATP- M a r 28, 1.990 TIME- ! 4 ; 5 7 . 4 8 o 9 D +) 400 5 0 0 6 0 0 7 0 0 W a v e l e n g t h (nm) PROJECT- t r a n s m i s s i o n o f a g i n g f i l t e r s SAMPLE- 2 aqanq f i l t e r s ( w h i te s t a n d a r d ) CD 1 1 ! ^ ^ 2 0 i i • I i LABELS Ulom Qb.s Smpl S r c d A 2d A a -C 2d C c 065 2d D d ID o \ 5 6 0 -x y Z A ; 74. 63 65. -14 J3. 37 D 52 .3] 63. 37 53.42 a A D) 61 .05 63 .34 54.36 d \ ^e \ c \ 6 0 0 \ 6 2 0 x y A) 0 .47J25 0 .4J286 J> 770 O 0.33750 0.34320 Q.) 0. 3.3365 0. 355J3 d DATE-- Mar 2B, 1390 TJME- 1 4 ; 5 4 ; S 3 . N ^ 8 0 , i i i i i 0- 2 0 . 4 0 . 6 0 . 3 o X C r-0 L O _ f\i 400 5 0 0 6 0 0 700 W a v e l e n g t h ( n m ) PROJECT '• t r a n s m i s s i o n o f a g i n g f i l t e r s SAMPLE 1 3 a g i n g f i l t e r s ( w h i l e s t a n d a r d ) 115 CD i i 220 i i i ; i LABELS I l i u m Ob.s SftifJ Src O N= 540 A ?.d A a -C 2d C c Q65 2d • d ID O V 560 -X V Z A) 6J.26 52 . ^ 5 12.93 , SOD ,580 Z) 50.06 50.50 41.21 D) 48. 73 50. 45 .38. ! J > o I d c a A 3 \ 6 0 D \, 520 A) 0 . 4 B 3 7 J 0.-U4JS \ j 770 f) 0 . 3 5 3 1 ] D.356J7 CM DJ> 0.3543? 0.36747 o , 480 DATE; .Mar 28, 1990 TIME; J 4= -49: 13 . NJ^BO i i i i 0. 2 0. 4 0.6 0.3 c X o _ oo 400 500 600 700 W a v e l e n g t h (nm) PROJECT^ t r a n s m i s s i o n o f aqjnq f i l t e r s SAMPLE- 4 aging f i l t e r s ( w h i te s t a r d o r d) 116 LA8ELS JJJurti Qbs SmpJ S r c A 2d A a C 2d C c 065 2d D d X y A) 48.95 40.95 C) 39 .00 38 .39 D) .33. 00 33. 83 Z 8. 90 27. 92 25. 86 x y A ; 0.43550 0 .^ j 446 O 0.36360 0.36755 D) 0.37003 0 .378J6 DATE. Mar 23. 1990 TIME; ! 4 : 4 5 : 5 J 400 5 0 0 6 0 0 700 W a v e l e n g t h (nm) 

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