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Short-term memory and cerebral excitability in elderly psychiatric patients Hannah, Farrell J. 1964

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SHORT-TERM MEMORY AND CEREBRAL EXCITABILITY IN ELDERLY PSYCHIATRIC PATIENTS  by F a r r e l l J . Hannah, B.A.  A Thesis Submitted i n P a r t i a l Fulfillment of the Requirements f o r the Degree of Master of Arts i n the Department of Psychology  We accept t h i s thesis as conforming to the required standard  The University of B r i t i s h Columbia August, 1964  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 per-  mission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that, copying or publication of this thesis for financial gain shall not be allowed without my written permission*,  Department of The University of British Columbia, Vancouver 8 , Canada  i ABSTRACT The purpose of t h i s thesis was to investigate  short-term  memory disorder i n elderly, psychiatric patients and to attempt to relate t h i s disorder to the concept of "neural e x c i t a b i l i t y " . There i s no doubt that some elderly, psychiatric patients suffer from a short-term memory d e f i c i t .  Many investigators  have reported that patients with diagnoses of senile psychosis or psychosis with cerebral a r t e r i o s c l e r o s i s experience serious d i f f i c u l t y with " i n i t i a l learning" or the immediate r e c a l l of new, or at least freshly presented, s t i m u l i .  A number of  studies have suggested that t h i s short-term memory disorder may be the result of a disruption i n one of the mechanisms which has been proposed to account for the a b i l i t y of young, adult subjects to respond sequentially to stimuli presented eously through d i f f e r e n t sensory channels.  simultan-  One of these  mechanisms has been termed the "p system", which only passes information successively; the other, the "s system", which can contain simultaneously  information from two channels.  l a t t e r mechanism i s the short-term  This  store which i s required f o r  the e f f e c t i v e handling of simultaneously  presented, dichotic  s t i m u l i , and which i s apparently the defective mechanism i n elderly, psychiatric patients with memory disorder. A binaural, simultaneous stimulation experiment was conducted.  Two groups of 20 elderly, psychiatric patients (one  with c l i n i c a l l y ascertained memory disorder and the other out such disorder) were tested using tape-recorded d i g i t s . Within these two main groups the conditions of r e c a l l were  with-  ii manipulated  f o r the purpose of examining what effect the pres-  c r i p t i o n of the order of r e c a l l would have upon the a b i l i t y of the patients to r e c a l l the binaural d i g i t s .  Half of the sub-  jects from each main group were told before the presentation of the d i g i t s which channel they would be required to reproduce f i r s t , and the other h a l f was told after the presentation. The general experimental hypotheses were that, under the "before" condition, the memory-disordered subjects would have s i g n i f i cantly greater d i f f i c u l t y r e c a l l i n g the stored d i g i t s (second channel recalled) than would the non-memory-disordered subjects; t h i s difference would be magnified i n the "after" condition. Although the results from some portions of t h i s experiment were not f u l l y i n accord with expectation, they a l l were i n the predicted d i r e c t i o n .  Several p o s s i b i l i t i e s were advanced i n an  attempt to account f o r t h i s f a i l u r e to achieve s t a t i s t i c a l s i g nificance, and f o r some of the d i s p a r i t i e s between present r e sults and those from previous studies conducted along similar lines.  However, the experimental findings did lend weight to  the idea that i n some elderly, psychiatric patients there i s a breakdown i n the short-term storage system of the type proposed by previous investigators. The underlying cause f o r the short-term memory d e f i c i t of some elderly, psychiatric patients may be a reduction i n the neural e x c i t a b i l i t y involved i n the short-term storage process. A current neuropsychological model proposes a two-stage process of memory functioning: reverberatory a c t i v i t y and permanent  iii changes i n the nervous system as a r e s u l t of t h i s a c t i v i t y . A second experiment was  conducted using a cumulative learning  paradigm with the aim of examining the efficiency of these stages i n elderly, psychiatric patients.  E s s e n t i a l l y the  same two groups of subjects were again tested with a l i s t of repeated and non-repeated series of d i g i t s .  The hypothesis  here was that, i n contrast to the control subjects, the perimental  subjects would not display cumulative learning of  the repeated series of d i g i t s . hypothesis,  ex-  In supporting the experimental  the results also i n d i r e c t l y reinforced the notion  that elderly, memory-disordered patients suffer from a reduct i o n i n the energy of the e l e c t r i c a l o s c i l l a t i o n s and/or an impedance of the neural network, both of which would mitigate against any s t r u c t u r a l modification based on reverberations. Although the experimental subjects i n these studies a l l displayed a severe short-term memory dysfunction, i t was  sus-  pected that they were not t o t a l l y incapable of learning, provided they were given s u f f i c i e n t opportunity for practice. The t h i r d and f i n a l experiment i n t h i s thesis dealt with the s e r i a l learning of words which were to be recalled or recognized by the same subjects involved i n the f i r s t two It was  studies.  expected that the memory-disordered patients would be  i n f e r i o r to the non-memory-disordered on both a r e c a l l and r e cognition task, but that both groups would show evidence of learning over a series of t r i a l s , the control group displaying the greatest amount of improvement under both conditions.  The  iv experimental results suggest that at l e a s t some learning does occur even where the patients exhibit gross memory disorder but that there i s a d e f i n i t e l i m i t to the amount of material which can be learned by these patients. Taken together, the results of these three experiments lend support to the notion that the memory disorder manifested by some elderly, psychiatric patients may be referable to a reduction i n cerebral reverberatory a c t i v i t y which makes longer-term learning v i r t u a l l y  impossible.  viii ACKNOWLEDGEMENTS  To my thesis advisor, Dr. William K. Caird, I extend my most sincere appreciation for his painstaking guidance of the work reported i n t h i s thesis and f o r h i s generous donations of "free" time f o r our consultations i n c r i t i c a l l y evaluating and editing the manuscript. I would also l i k e to thank Dr. Thomas Storm f o r his reading of the f i n a l draft of the t h e s i s . Thanks are due the medical and nursing s t a f f at Valleyview Hospital, Essondale, B r i t i s h Columbia f o r t h e i r cooperation.  Dr. B.F. Bryson, Miss E. Johnstone and a l l  the charge nurses of the Valleyview wards deserve special recognition f o r f a c i l i t a t i n g t h i s research. I would also l i k e to thank Mrs. P. Waldron f o r caref u l l y typing the f i n a l draft of t h i s t h e s i s . Of course, I gratefully acknowledge the e f f o r t s of my wife, Audrey, whose continuous patience and encouragement immeasurably contributed toward the completion of this thesis. Part of t h i s research was carried out with the assistance of a Canadian National Mental Health Grant (Project No. 609-5-145).  V  TABLE OP CONTENTS INTRODUCTION  1  CHAPTER I Short-term Memory i n Elderly Psychiatric Patients  2  CHAPTER II Cerebral E x c i t a b i l i t y and Short-term Memory  14  CHAPTER.Ill Memory Disorder and Simultaneous Binaural Digit Performance  23  CHAPTER IV Memory Disorder and Cumulative Learning.... 43 CHAPTER V Memory Disorder and S e r i a l Learning  48  CHAPTER VI Conclusions  55  REFERENCES  58  APPENDIX  62  vi TABLES Table  Page  1.  Means, standard deviations, and the significance of the differences between the means of the experimental and control groups on the matching criteria.  2.  Means, standard deviations, and the significance of the differences between the E and C\ groups on the matching c r i t e r i a .  35  3.  Means, standard deviations, and the significance of the differences between the E, and C, groups on the binaural d i g i t task.  35  4.  Means, standard deviations, and the significance of the differences between the E and C groups on the matching c r i t e r i a .  37  5.  Means, standard deviations, and the significance of the differences between the E and C groups on the binaural d i g i t task.  37  6.  Means, standard deviations, and the significance of the differences between the E^ and E groups on the matching c r i t e r i a .  39  7.  Means, standard deviations, and the significance of the differences between the E^ and E groups on the binaural d i g i t task.  39  8.  Means, standard deviations, and the significance of the differences between the and C groups on the matching c r i t e r i a .  40  9.  Means, standard deviations, and the significance of the differences between the and C groups on the binaural d i g i t task.  40  10.  Mean difference scores, standard deviations, and the significance of the mean difference scores between f i r s t and second channel r e c a l l f o r each d i g i t l e v e l within the four subgroups.  42  11.  Means, standard deviations, and the significance of the differences between the means of the experimental and control groups on the matching criteria.  k  &  &  32  46  vii Table  Page  12.  Means, standard deviations, and the significance of the differences between the means of the experimental and control groups on the repeating and non-repeating series of d i g i t s . .  13.  Means, standard deviations, and the significance of the differences between the means of the experimental and control groups on the r e c a l l and recognition task, t r i a l s 1 and 5.  14.  Means, standard deviations, and the significance of the differences between the means on t r i a l s 1 and 5 of the r e c a l l and recognition tasks f o r the experimental group.  15.  Means, standard deviations, and the significance of the differences between the means on t r i a l s 1 and 5 of the r e c a l l and recognition tasks f o r the control group.  46  51  51  53  - 1 INTRODUCTION There i s certainly no consensus among investigators today as to the c r u c i a l aspects of human learning and 'memory . 1  Both physiological and psychological formulations concerning memory function suffer from an incompleteness which underscores the d i f f i c u l t y i n evolving a theory of memory function which w i l l encompass the presently known facts from the f i e l d s of psychology, neurophysiology, and biochemistry.  To date,  no one system of explanation has been able to provide a s a t i s factory account of what actually does occur when something i s 'committed to memory', nor i s such an explanation l i k e l y to appear i n the near future (Gomulicki, 1953).  The problems  being studied by various investigators often seem rather d i s parate and, i n some cases, appear unrelated.  The range of  experimentation with memory function may extend anywhere from the nature of the genie material within the neurons of the brain (Gaito, 1961; 1963), through the 'tagging' and coding of information  'chunks' (Yntema and Trask, 1963; Hunt, 1963),  to the storage and r e t r i e v a l of items-to-be-remembered from short-term memory and from long-term memory (Melton, 1963). The broad aim of the present thesis i s to examine one aspect of memory functioning, s p e c i f i c a l l y short-term storage. The subjects i n these investigations w i l l be elderly, psychiat r i c patients characterized by a gross memory disorder. The experimental results w i l l be discussed i n r e l a t i o n to previous investigations and i n terms of some neuropsychological elements of memory functioning.  CHAPTER I Short-term Memory i n E l d e r l y Psychiatric Patients There i s a body of evidence to support the notion that some elderly, psychiatric patients suffer from a memory d i s order which i s apparently due to dysfunction or breakdown of processes underlying short-term  retention.  Botwinick and  Birren (1951)» f o r example, found that a group of elderly patients with diagnoses of senile psychosis or psychosis with cerebral a r t e r i o s c l e r o s i s performed quite poorly on " i n i t i a l learning" subtests of the Babcock-Levy (1940) examination when compared with a control group free from these disorders. Dorken and Greenbloom (1953)» investigating s i m i l a r groups of patients, demonstrated that there i s also impairment of performance on tasks requiring speed aid.'.constructive s h i f t i n g of thought.  On the other hand, where habitual tasks and  c r y s t a l l i z e d thought were evaluated without a time factor, they discovered that the performance of the senile patients was more adequate.  In t h e i r study of the amnestic syndrome  i n various organic conditions, Krai and Durost (1953) maintained that the phase of the remembering process that operates i n the recording and assimilation of new experiences, t o gether with i t s underlying mechanism, seems to be the most vulnerable i n cases of cerebral involvement and therefore the most noticeably affected.  This i s true of senile patients  where a generalized brain damage may be present.  Welford (1956), i n h i s review of some of the theory and research applicable to aging and memory, proposed a series of 'essential stages' of the learning process.  These stages, he  maintained, must be traversed before learning can occur and subsequently be manifested by the individual. 1.  The stages are:  Perception and comprehension of the material to be  learned. 2.  Some form of short-term storage of material f o r long  enough to enable long-term retention to occur. 3.  Retention v i a r e l a t i v e l y enduring tissue change.  4.  Recognition of a further situation demanding the: r e -  use of t h i s material rather than any other. 5.  Recall of the material retained.  6.  Use of the material, with adaptation, i f necessary, i n  the new situation. Welford suggests that 'poor memory' may be the result of l i m i t i n g factors i n one or other of the s i x stages.  He has  suggested that there i s s u f f i c i e n t experimental evidence to r e inforce the idea that the key to understanding learning d e f i c i t s as they occur with aging and i n senile patients may l i e i n the short-term memory of stage two, and he asserts that a gross short-term memory d e f i c i t i s common i n senile states.  Bromley  (1958), Inglis and Caird (1963B), Krai (1962), and Wimer (i960) have supported, with experimental findings, Welford's contention that the learning d e f i c i t found i n elderly persons  - 4 may be the result of an impairment i n the short-term memoryprocess. The common observation that old age i s often accompanied by ' f a i l i n g memory* and that i n senile states there i s also a common  d i f f i c u l t y with 'recent memory', has prompted a good  deal of research i n t h i s area.  For example, I n g l i s (1957) has  regarded 'memory function' as part of the learning process and he adheres to the d e f i n i t i o n whereby 'learning' i s used to designate  changes i n behavior during a specified time or  to a certain l e v e l , and 'retention' to mean any measured persistance of these changes post-practice.  He demonstrated that  elderly, psychiatric patients who have c l i n i c a l l y - a s c e r t a i n e d memory disorder appear to suffer from a deficiency i n t h e i r a b i l i t y to record or acquire information which i s presented for them to learn.  He found that memory-disordered, elderly,  psychiatric patients could be d i f f e r e n t i a t e d from a non-memory -disordered group, matched for age and Wechsler Verbal Scale weighted score (Wechsler, 1955)» i n terms of t h e i r performance on the acquisition (learning) t r i a l s of a paired associate learning test of his own design (Inglis, 1957; 1959A).  From  t h i s finding, he concluded that a defect i n the f i r s t stage of learning, the acquisition phase, i s a c r u c i a l aspect of the memory disorder exhibited by some elderly, psychiatric patients.  In other words, impairment i n 'new learning a b i l i t y ' ,  rather than i n the 'running o f f of old habits', may be an  - 5 important factor i n the memory dysfunction of these patients. A l a t e r study (Inglis, 1959B) confirmed these findings and extended them "by showing that, while the d i s a b i l i t y is; exhibited p r i n c i p a l l y i n the acquisition stage, these patients also displayed a retention defect when required to r e t a i n the new associations of the paired associate learning task.  However,  a l l of the studies mentioned thus f a r strongly suggest that there i s a primary defect in the acquisition phase of learning i n those elderly, psychiatric patients who display gross memory disorder. Despite the fact that i t i s d i f f i c u l t to separate the learning process i n terms of acquisition and retention i n order to study each of them experimentally,  i t i s possible to think  of learning i n terms of a "pre-consolidation" phase and a "consolidation" phase (Caird, 1962), where the l a t t e r i s dependent upon the occurrence of the former.  These w i l l be  discussed i n greater d e t a i l i n Chapter I I . However, with these concepts i n mind, a v a r i a t i o n of the Wechsler (1955) d i g i t span test devised by Broadbent (1957) has been employed i n several investigations (Caird and I n g l i s , 1961;  I n g l i s and Caird, 1963A,B: I n g l i s and Sanderson, 1961)  i n the hope of accurately measuring short-term  retention (pre-  consolidation) and gaining a better understanding of i t s dysfunction.  B r i e f l y , Broadbent's (1957) procedure involves  the administration of d i g i t s simultaneously  to d i f f e r e n t  -  6  -  sensory channels (for example, to "both ears at once, or to both the eyes and the ears at once).  He maintains that the  sequential r e c a l l of the d i g i t s so presented not only involves a straight perceptual process, but also a simple storage system which i s necessary f o r short-term memory.  In one study  (Broadbent, 1957), he reported that when sets of d i g i t s were relayed binaurally, through headphones at the rate of two per second, to young, normal, adult subjects, one-half of the span to one ear and the remaining half to the other ear simultaneously, then the r e c a l l of these d i g i t s tended to be sequential. The half-spans remained as separate i n r e c a l l as they had been i n administration.  In other words, he found that none of the  items from one h a l f span intruded into the other half-span. Furthermore, under these conditions, the half-span recalled f i r s t generally contained called second.  fewer errors than the half-span re-  That i s , there was a "serial-order e f f e c t " .  Broadbent (1957; 1963) proposes that there are two kinds of mechanisms involved i n the perception and r e c a l l of simultaneously presented d i g i t s .  There i s a "p-meonanism", which  can only pass information successively, and an "s-mechanism", which can contain simultaneously channels.  information from the two  The suggestion i s that the s-system i s only i n -  volved under conditions of dichotic stimulation and not under those of orthodox d i g i t span performance. s-system might be:  He states that the  "....merely an emergency device introduced for the special case i n which excess i n f o r mation arrives while the p-system i s a l ready f u l l y occupied with another channel" (1957, p . l ) . In a recent a r t i c l e (Broadbent, 1963), he has outlined an information-flow model which suggests that the human perceptual system has a limited capacity.  When information  comes into the nervous system i t passes through t h i s limited capacity channel, which means that i t i s d i f f i c u l t f o r the organism to 'absorb' other information simultaneously. Some of the overload, then, must pass through the limited capacity channel to be held i n short-term storage.  However, t h i s i s  e f f i c i e n t only as long as these items of information can pass repeatedly through the same limited capacity channel as that by which they i n i t i a l l y arrived.  So long as they conform to  t h i s l a t t e r requirement, the information-items can be stored i n this way i n d e f i n i t e l y .  Should the limited capacity channel  become unavailable f o r some reason (for example, due to the admission of some fresh information-items from the environment, or due to overloading i n a simultaneous stimulation situation), then the e a r l i e r information w i l l not be available f o r r e c a l l because of rapid decay and the i n t e r f e r i n g effects of additional stimuli.  In short, Broadbent i s emphasizing the  f l e e t i n g nature of short-term memory as t h i s i s influenced by interference and decay of the memory trace (Broadbent and Heron, 1962).  - 8 Of even greater relevance to the present thesis i s Broadbent's (1957) notion that the incoming items of informat i o n may be held i n the temporary, short-term storage at a stage p r i o r to selection f o r r e c a l l (that i s , p r i o r to the r e t r i e v a l process).  Because of the s u s c e p t i b i l i t y of the  stored items to interference and decay processes, such items may become l o s t - t o - r e c a l l due to the time i n t e r v a l between the i n i t i a l storage of these excess items ( i n the  simultaneous  stimulation situation) and the actual selection of the i n f o r mation to be recalled by the i n d i v i d u a l .  In one study,  Broadbent (1957), using the method of binaural stimulation with normal subjects, set out to examine t h i s aspect of the short-term storage system by specifying the order of r e c a l l for the two half-spans.  Some of h i s subjects were told which  ear to report f i r s t before the presentation of the stimuli (the  known or "k" condition), while others were told which ear  to report f i r s t after the stimuli had been presented (the ambiguous or "a" condition). Broadbent hoped to determine: "...whether the s-system, necessary for the simultaneous stimulation case, i s operating even i n successive stimulation cases. I f i t i s , and the p-system i s merely a l a t e r stage of the normal progress of information through the man, i t should be possible to prescribe a particular order of r e c a l l at any time before r e c a l l ; even after stimulation. The p-system could then take i n the information i n the r e quired order, and response would show normal e f f i c i e n c y and a normal s e r i a l order e f f e c t . On the other hand, i f the p-system provides the normal route between input and output, and the s-system i s merely an extra store f o r excess information, then one or the other  channel would deliver i t s information to the p-system immediately on stimulation. An i n struction to r e c a l l i n a p a r t i c u l a r order, a r r i v i n g after stimulation, could not therefore affect the order of input to the p-system, but only the order of output. The d i f ference between the two orders would give... an absence of s e r i a l order e f f e c t " (1957,p.2) In other words, i f i t were the case that a l l the stimuli passed through the s-system before entering the p-system, then there would be more errors i n the second half-span recalled than i n the f i r s t , and this should occur whether the order was prescribed under either the "k" or the "a" condition. However, i f only part of the stimuli passed through the s-system and the other part went straight to the p-system, then the s e r i a l order effect would not be expected i n the "a" condition (but would be i n the "k" condition).  This lack of s e r i a l order effect would  only occur i f the subject had processed f i r s t that half-span which he i s called upon to reproduce l a s t .  I f i t so happened  that he had processed f i r s t that half-span which he was, i n fact, called upon to reproduce f i r s t , then the s i t u a t i o n would be similar to the "k" condition, and one might then expect the s e r i a l order effect to appear. Although Broadbent's (1957) results tended to confirm his hypothesis about the effect of the "k" condition (the s e r i a l order effect did occur), the "a" condition hypothesis was not so clearly-supported (the s e r i a l order effect also occurred i n t h i s condition, but only i n the i n i t i a l stages of practice; i n l a t e r stages, i t v i r t u a l l y disappeared).  While these re-  sults were f a r from unequivocal, he concluded that i n early  - 10 practice stages the strategy adopted by the subject would be to have a l l the incoming information enter the s-system and l a t e r pass to the p-system when required; l a t e r i n practice, incoming information may pass straight into the p-system, with excess being held i n the s-system.  That i s , despite  lack of clear-cut evidence i n support of h i s o r i g i n a l hypothes i s , Broadbent has, i n effect, accepted h i s i n i t i a l notion that during orthodox d i g i t span performance, or ordinary immediate memory, information probably enters the p-system at once without f i r s t passing through the s-system.  In addition,  t h i s n o n - u t i l i z a t i o n of the s-system during orthodox d i g i t span performance may be the basis f o r the f a i l u r e , to find a decreased efficiency of ordinary d i g i t span i n elderly, psyc h i a t r i c patients suffering from a short-term memory d e f i c i t (Caird and I n g l i s , 1961: I n g l i s , 1957; Inglis and Caird, 1963A, B;  Inglis and Sanderson, 1961). As previously mentioned, Broadbent (1963) maintains that  the  items of information being handled by the short-term store  are  subject to f a i r l y rapid decay, and t h i s i s the reason  that, i n the simultaneous stimulation situation, subjects do perform more poorly on the second (stored) half-span than they do on the f i r s t (passed) half-span recall ed. the  I f such i s  case, then one would expect that elderly, psychiatric pa-  tients who d e f i n i t e l y exhibit c l i n i c a l memory disorder should perform s i g n i f i c a n t l y more poorly on the second half-span r e called than should a comparable group of non-memory-disordered psychiatric patients, and that the f i r s t half-spans recalled  - 11 should he of equal efficiency f o r both groups.  That i s , i t  i s suggested that elderly, psychiatric patients, who have c l i n i c a l l y - a s c e r t a i n e d memory disorder, suffer from an impairment i n , or deterioration of, the short-term storage mechanism postulated by Broadbent.  There i s a body of evidence  to support t h i s contention (Caird, 1962; Caird and I n g l i s , 1961; Inglis and Sanderson, 1961). The investigation conducted by Inglis and Sanderson (1961) was s p e c i f i c a l l y designed to test the hypothesis that memory disorder i n elderly, psychiatric patients i s indeed related to a breakdown of the short-term mechanism.  Using a v a r i a t i o n  of Broadbent's (1957) method of dichotic stimulation, they presented d i g i t s , ranging i n number from one to four d i g i t s per half-span to memory-disordered and non-memory-disordered of elderly, psychiatric patients.  groups  They found s i g n i f i c a n t  differences between experimental and control groups i n a b i l i t y to reproduce the second or stored half-span, with the former group displaying poorer performance than the l a t t e r group on a l l lengths of d i g i t s used.  The authors have suggested:  "... that the c l i n i c a l picture of memory disorder i n elderly, psychiatric patients i s based, at least i n part, upon a breakdown of the kind of storage mechanism (s system) proposed by Broadbent to account for the capacity of young, normal adults to respond successively to information delivered to them simultaneously" (p. 711) An interesting and unexpected occurrence was noted i n the Inglis and Sanderson study; there were also s i g n i f i c a n t  - 12 differences between the groups i n the f i r s t half-spans recalled f o r three- and four-digit half-spans.  The  could offer no ready explanation f o r t h i s finding.  authors What may  have occurred, however, i s that the binaural task, at the three- and four-digit l e v e l , simply became too d i f f i c u l t for the memory-disordered group and may  even have come to involve  short-term storage on the dominant channel ( f i r s t half-span r e c a l l e d ) , although t h i s same effect did not appear i n the orthodox digit-span s i t u a t i o n . The differences between a l l the f i r s t and second h a l f span reproductions were s i g n i f i c a n t within the group i n the Inglis and Sanderson study.  experimental  That i s , the memory  disordered group did show the s e r i a l order effect i n t h e i r r e c a l l of the binaural d i g i t s .  On the other hand, the d i f f e r -  ences were not s i g n i f i c a n t within the control group except when the three- and f o u r - d i g i t l e v e l was again reached.  Per-  haps t h i s l a t t e r result occurred because the one- andtwod i g i t situations were not d i f f i c u l t f o r the control subjects, whereas the three- and four-digit situations were more taxing on t h e i r short-term storage systems.  This would appear reason-  able since the average orthodox d i g i t span of these patients was approximately  six d i g i t s .  At any rate, the results lend  convincing support to the o r i g i n a l hypothesis ;about the shortterm storage system breakdown i n some elderly, psychiatric patients. This experiment was replicated and extended to the crossmodality situation (visual and auditory channels employed  - 13  -  simultaneously) by Caird and Inglis (1961).  The results con-  firmed Inglis and Sanderson's (1961) findings; they were, i n a l l essential aspects, the same.  This was true whether the  half-spans were presented a u d i t o r i l y (to both ears) or v i s u a l l y and a u d i t o r i l y (to eyes and ears together). On the basis of these findings, Caird (1962) has stated that these r e s u l t s : "...serve to reinforce the suggestion, that defects i n that kind of storage system which has been adduced to explain successive r e sponses to simultaneous stimulation may play an important part i n disorders of memory i n the elderly" (p. 54). Recently  (Inglis and Caird, 1963B), binaural d i g i t per-  formance has been observed over a wide age range (eleven to seventy years) of normal subjects.  The expectation was that  the reproduction of the f i r s t half-sets recalled would not be affected by advancing years, whereas the reproduction of the second (stored) half-sets would be adversely affected by aging. The results were i n accord with expectation, which suggests that there may well be a short-term storage mechanism or process which deteriorates with age.  - 14 CHAPTER I I C e r e b r a l E x c i t a b i l i t y and Short-term  Memory  As o u t l i n e d i n Chapter I , there i s reasonable to support  evidence  the suggestion t h a t memory d i s o r d e r i n e l d e r l y ,  p s y c h i a t r i c p a t i e n t s may be the r e s u l t processes u n d e r l y i n g short-term  o f a breakdown i n c t h e  storage.  A p o s s i b l e cause o f  t h i s d y s f u n c t i o n i n short-term memory may be a lowered energy of r e v e r b e r a t o r y o s c i l l a t i o n s i n v o l v e d i i fee short-term  (reduced  cerebral e x c i t a b i l i t y )  storage process.  concerned with some evidence  t o support  T h i s chapter i s  this latter  P a u l i n g (1961) p o i n t s out, i n h i s molecular  contention.  theory o f  g e n e r a l anaesthesia, t h a t a k i n d o f e l e c t r i c a l o s c i l l a t i o n may u n d e r l i e both consciousness or short-term) memory.  and ephemeral ( r e v e r b e r a t o r y  He s t a t e s t h a t these o s c i l l a t i o n s may  be d i s c u s s e d i n terms o f an e x c i t i n g mechanism and a supporting s t r u c t u r e (the b r a i n , with i t s n e u r o l g i a l c e l l s , neurons, and synaptic inter-connections).  The energy o f these  electrical  o s c i l l a t i o n s and, t h e r e f o r e , the r e s u l t a n t s t a t e s o f consciousness and ephemeral memory, are assumed t o be the product of the a c t i v i t y o f the e x c i t i n g mechanism and the impedance o f the n e u r a l network.  Thus, i n e f f i c i e n c y  f o r example, may be the r e s u l t  o f ephemeral memory,  o f a decrease jn.the a c t i v i t y o f  the e x c i t i n g mechanism, o r o f an i n c r e a s e i n the impedance o f the supporting n e u r a l s t r u c t u r e s , o r o f both. that s e d a t i v e s such as b a r b i t u r a t e s operate e x c i t i n g mechanism t o decrease i t s a c t i v i t y .  P a u l i n g suggests  by a c t i n g on the On the other  - 15 hand, general anesthetics of the non-hydrogen-bonding type may  increase the impedance of the encephalonic network of  conductors.  They achieve t h i s by forming, through the  c r y s t a l l i z a t i o n of the encephalonic f l u i d , hydrate microcrystals i n the network, p a r t i c u l a r l y i n the synaptic regions. These i n t e r f e r e with freedom of ionic movement and so impede the e l e c t r i c a l o s c i l l a t i o n s despite, t h e o r e t i c a l l y , the continued functioning of the exciting mechanism. Pauling's hypothesis about the s p e c i f i c action of barbiturates on the exciting mechanism, appears relevant to an i n vestigation conducted by Weinstein et a l (1953).  Weinstein  and his associates stated that one of the c l i n i c a l uses of sodium amytal has been in/the study of behavior i n diseases of the nervous system.  In patients who  showed denial of i l l n e s s  and disorientation f o r time and place, i t was  observed that  once these symptoms had cleared c l i n i c a l l y , they could be r e produced by intravenous  administration of sodium amytal.  They  also report that t h i s drug can produce patterns of disorientation and denial of i l l n e s s i n patients with known brain disease who who  had previously not shown such behavior.  Patients  complained of loss of memory early i n the course of vas-  cular or degenerative diseases showed positive r e s u l t s , i n displaying the phenomena, as well.  The lowered tolerance f o r  sodium amytal exhibited by the brain damaged patients i n t h i s study suggests that there may  have been an even greater-than-  normal impedance i n the neural networks (Pauling, 1961).  - 16 On the other hand, the raised thresholds found i n anxious patients by Shagass and Naiman (1956) might, as the authors suggest, be due to the greater a c t i v i t y of excitatory mechanisms intlaese patients, including the action of the r e t i c u l a r activating system.  This would appear reasonable i n the l i g h t  of Pauling's (1961) theory. The results of a number of electroencephalographic investigations would appear to be relevant to the present thesis. A l l of these studies, a sample of which appears below, suggest that there i s an association between slow wave a c t i v i t y i n t e l l e c t u a l deterioration and memory dysfunction by some elderly, psychiatric patients.  and  exhibited  For example, senile  mental deterioration i s associated with EEG- changes.  Elderly  patients with chronic brain syndrome display s i g n i f i c a n t l y more diffuse slow wave a c t i v i t y i n the theta (4 - 7 c.p.s.) and delta (1 - 3 c.p.s.) bands than do elderly patients without t h i s syndrome (Barnes et a l , 1956;  Obrist and Henry, 1958).  Where confusion and i r r i t a b i l i t y are characteristic of the patient, there i s also a high incidence (Liberson and Seguin, 1945).  of slow waves  Similarly, organic mental signs  are reported by Luce and Rothschild  (1953) to be accompanied  by a slow alpha rhythm.  In one study (Mundy-Castle et a l ,  1954)  found between EEG- abnormality and  a relationship was  severity of senile dementia, where the measure of this based on memory, orientation, and organization  was  of thought.  There are many more studies i n t h i s general area, some  - 17 of which have been recently reviewed by Caird (1963).  As  mentioned e a r l i e r , abnormal slow wave a c t i v i t y appears to be related to memory dysfunction and degree of pathology i n patients suffering from senile dementia.  Indeed, i t has been  suggested (Obrist and Henry, 1958) that diffuse slow wave a c t i v i t y i s the most r e l i a b l e BEG index of mental deteriorat i o n , and slow wave a c t i v i t y may i t s e l f be a manifestation of reduced neural e x c i t a b i l i t y . Glickman (1961) and Caird (1962) have reviewed some of the other evidence which supports the concept of reduced cerebral e x c i t a b i l i t y as the possible cause of short-term memory disorder.  Glickman asserts that, since the turn of the  century, theorists have speculated about a neural f i x a t i o n process responsible f o r e f f i c i e n t retention after the i n i t i a l stimulus has been presented and withdrawn.  Interference with  t h i s process was presumed to adversely affect the organism's a b i l i t y to remember stimuli to which i t had been exposed. c i t e s several c l i n i c a l observations  He  and experimental studies  which are concerned with retrograde amnesia and i t s r e l a t i o n ship to brain trauma, electroconvulsive shock, anoxia, hypoand hyperthermia, anaesthesia, brain stimulation and p a r t i a l ablations.  Caird (1962) has also reviewed these factors and  t h e i r influence upon the memory trace, and he has extended the review to include the effects of aging and of senile pathology as well.  Glickman maintains that under each of these s i t u a -  tions, the consolidation process i s hindered, since the subject's  - 18 memory f o r recent events i s impaired, whereas more remote associations are not so affected.  In other words, consolidation  seems to depend upon reverberatory neural a c t i v i t y .  He says:  "The basic supposition i s that reverberatory a c t i v i t y maintains the memory u n t i l the permanent changes underlying f i x a t i o n of the trace have been completed. This dual process hypothesis of memory f i x a t i o n has the advantage of explaining why interference with neur a l a c t i v i t y immediately after 'learning' blocks retention while similar procedures at a l a t e r time do not" (p. 229). Similarly, Caird (1962) concluded from his investigations that a dual system i s involved i n memory function.  The f i r s t  mechanism i n t h i s system, he suggests, i s a "pre-consolidation phase"; the second i s a "consolidation phase". to correspond to Hebb's (1949) "reverberatory his " c e l l assemblies and phase sequences".  These appear  c i r c u i t s " and  B r i e f l y stated,  Hebb has argued that repeated stimulation w i l l gradually lead to the development of a c e l l assembly (a diffuse structure comprising c e l l s i n the cortex and diencephalon mainly) capable of b r i e f , closed system a c t i v i t y , able to deliver f a c i l i t a t i o n to other such systems, and usually having a s p e c i f i c motor f a c i l i t a t i o n .  A series of such events or systems con-  s t i t u t e s a phase sequence.  He has proposed that the formation  of c e l l assemblies allows time for s t r u c t u r a l changes to occur i n the brain and that t h i s i s the basis for learning.  In  other words, a reverberatory mnemonic trace might 'carry the memory' u n t i l a more permanent change, possibly synaptic growth, occurs and the 'memory o f a p a r t i c u l a r event becomes more l a s t i n g or 'learned'. •  - 19 The theoretical views of Hebb (1949) and of Pauling (1961) are very s i m i l a r .  Pauling has stated that i t i s :  " . . . l i k e l y that consciousness and ephemeral memory (reverberatory memory) involve elect r i c o s c i l l a t i o n s i n the brain, and that permanent memory involves a material pattern i n the brain, i n part inherited by the organism and i n par transferred to the material brain from the e l e c t r i c pattern of the ephemeral memory" (p. l ) . Recently, Gerard (1963) has endorsed the same viewpoint i n his discussion of " f i x a t i o n time"; the time required for electrical-chemical a c t i v i t i e s to become material, s t r u c t u r a l formations i n the brain. 1962;  A l l of these investigators (Caird,  Gerard, 1963, Glickman, 1961, Hebb, 1949; Pauling, 1961)  adhere to the dual mechanism view of learning, and t h i s i s the position adopted by Broadbent (1957, 1963) regarding the dichotomy of short-term  and long-term memory function.  Simi-  l a r l y , they have expressed, at least i m p l i c i t l y , the notion of reduced cerebral e x c i t a b i l i t y as the possible cause of the disruption i n short-term memory under various conditions or situations (including those of senile pathology); t i o n of the short-term  the disrup-  phase of the dual system necessarily  interferes with the operation of the long-term or consolidation phase of the system. Assuming that short-term memory disorder i n elderly, psyc h i a t r i c patients i s due to the lowered energy of reverberatory o s c i l l a t i o n s , these individuals would be expected to show a s i g n i f i c a n t l y lower tolerance for sodium amytal, which reduces cerebral excitation (Pauling, 1961), than would a matched  - 20 control group without memory disorder.  An investigation by  Caird et a l (1963) supported t h i s expectation.  The memory-  disordered patients had s i g n i f i c a n t l y lower sedation-.and sleep thresholds than did the control group.  These findings lend  further support to the notion that memory disorder i n some elderly, psychiatric patients may be explainable by reduced neural e x c i t a b i l i t y . A cumulative learning study (Hebb, 1961) appears relevant to the position taken i n t h i s thesis since i t involves the relationship between the pre-consolidation and consolidation phases of memory.  O r i g i n a l l y , Hebb (1949) assumed the r e p e t i -  t i o n of d i g i t s i n a test of memory span to be a pure example of the a c t i v i t y trace (pre-consolidation phase or s-system). That i s , the presentation of a set of d i g i t s i n t h i s s i t u a t i o n would completely wipe out the preceding series; one a c t i v i t y trace would cancel out the previous a c t i v i t y trace and no structural change would occur.  He l a t e r modified his thinking  i n the l i g h t of the r e s u l t s of a study of cumulative learning (Hebb, 1961).  B r i e f l y , he presented to 40 college  students,  a l i s t of 24, nine-digit series, the subject being required to r e c a l l each series immediately a f t e r presentation.  Bach  of the 24 series was d i f f e r e n t except f o r every t h i r d one which was the same. The subject was not informed of t h i s r e p e t i t i o n . Hebb's question was: would this r e p e t i t i o n result i n d i f f e r e n t i a l performance between the repeated and non-repeated series?  That i s , would there be cumulative learning of the  - 21 repeated series?  I f , according to Hebb, i t i s only a case of  the d i g i t s becoming an a c t i v i t y trace, with no residue, then no cumulative learning should occur.  On the other hand, i f  learning does occur i n t h i s instance, i t can be concluded that some s t r u c t u r a l modification has occurred i n addition to whatever a c t i v i t y trace there may  be.  The r e s u l t s showed cumulative learning.  Performance on  the repeated series was much more e f f i c i e n t than on the repeated s e r i e s .  non-  Hebb concluded that:  "...a single r e p e t i t i o n of a set of d i g i t s ...produces a structural trace which can be cumulative. I assume that an a c t i v i t y trace can also be involved i n the actual r e p e t i t i o n , but i t i s the structural change which i s of interest here" (p. 43). Hebb maintains that, i n educated subjects, d i g i t s are highly practised material; associative connections already exist between any two d i g i t s , or, i n other words, the i n d i v i dual has learned many sequences i n which any d i g i t i s followed by any other d i g i t .  When he i s given a 'new  1  series of d i g i t s  to repeat, his memory f o r that series depends upon a further strengthening strengthening, I960; 1961).  of already-established  connections - a synaptic  although not necessarily neurobiotaxis This might help to explain why  (Milner,  orthodox d i g i t  span does not d i f f e r e n t i a t e between elderly, psychiatric pat i e n t s with memory disorder and those without (Caird and Inglis 1961;  Inglis, 1957;  Sanderson, 1961)  Inglis and Caird, 1963A; .Inglis and  and why  i t does not appreciably decline with  - 22 age as does learning i n general (Inglis and Caird, 1963B). The idea of cumulative learning would appear to be useful i n the examination of short-term storage and reduced cerebral e x c i t a b i l i t y i n the senium.  This w i l l be discussed i n some  d e t a i l i n Chapter IV. The following three chapters ( I I I , IV, and V) are concerned with investigations designed to examine, i n d e t a i l , some of the notions i m p l i c i t i n the foregoing review.  The  f i r s t of these i s concerned with a r e p l i c a t i o n of Broadbent's (1957) study of the effects of known and ambiguous r e c a l l i n a binaural situation and how these are related to short-term memory disorder i n some elderly, psychiatric patients.  The  second deals with the suggestion that these same patients w i l l not, because of t h e i r memory dysfunction, display cumulative learning using the Hebb (1961) paradigm.  F i n a l l y , an  attempt w i l l be made i n Chapter V to show that while some e l derly patients display a gross memory disorder, they are not t o t a l l y incapable of learning; given s u f f i c i e n t practice there i s some evidence of learning.  A l l of these investigations, i t  i s suggested, can be understood i n terms of the role that cerebral e x c i t a b i l i t y plays i n short and long-term memory. The experimental subjects i n these studies a l l display a severe short-term memory dysfunction. Their performance on some memory and learning tasks i s compared with that of a matched control group free of this disorder.  - 23 CHAPTER III Memory Disorder and Simultaneous Binaural Digit Performance This dichotic stimulation experiment had a dual purpose. Primarily i t was designed to c l a r i f y the notion that the memory dysfunction observed i n some elderly, psychjatric patients may be the result of a disruption i n the processes underlying short-term memory (Caird and Inglis, 1961; Inglis and Sanderson, 1961).  I t was also intended to examine what  effect the prescription of the order of r e c a l l  (Broadbent,  1957) may have upon the a b i l i t y of the patients to r e c a l l the binaural d i g i t s . Half of the subjects from both experimental and control groups were told which ear to report f i r s t before ("k" condition) the d i g i t s were presented; the other h a l f of each group was told which ear to report f i r s t after ("a" condition) the d i g i t s had been presented.  I f the memory disorder i s a short-  term storage defect, then under the "k" condition there should be no s i g n i f i c a n t difference between the groups i n the f i r s t half-span recalled; there should be a s i g n i f i c a n t difference between groups i n second half-span performance, with the experimental group being poorer i n r e c a l l than the control group. There should be a s e r i a l order effect i n both groups' performances, but with the experimental groups disparity between f i r s t and second half-span performance being greater than the control group's.  Under the "a" condition, there should be no  overall s e r i a l order effect observed i n either group, with  - 24 both groups performing poorly on both half-spans recalled. However, i t was expected that the performance of the experimental group on both half-spans would be s i g n i f i c a n t l y poorer than that of the control group. Method Subjects The experimental group consisted of twenty elderly, psyc h i a t r i c patients who were reported by nursing s t a f f to be suffering from gross, c l i n i c a l memory disorder, and who achieved a paired-associate learning test score of not less than sixty (Inglis, 1959A).  The control group of twenty patients was com-  posed of similar persons but who, according to the nursing s t a f f , had no gross memory disorder and who achieved a pairedassociate learning test score of not greater than t h i r t y . A l l of the subjects had been patients of Valleyview Hospital, Bssondale, B r i t i s h Columbia f o r not less than one and one-half years.  No known cases of l o c a l i z e d or f o c a l brain damage were  included i n the study. The age range of the experimental group was from 71 to 85; the control group range was from 73 to 85. The W.A.I.S. (Wechsler, 1955) Verbal Scale I.Q. range f o r the experimental group was 75 to 120; f o r the control group, i t was 84 to 110. There were 8 men and 12 women i n each of the two groups. Tests Wechsler Adult Intelligence Scale.  Experimental aid control  groups were equated i n terms of verbal a b i l i t y (Verbal Scale  I.Q.) and d i g i t span forward performance on the W.A.I.S. Paired-associate Learning Test.  As previously mentioned, the  two groups were established primarily on the basis of performance on a paired-associate learning test, which i t s e l f has shown the a b i l i t y to discriminate between memory-disordered and non-memory-disordered, elderly, psychiatric patients (Caird et a l , 1962; Inglis, 1959A). bal  The P.A.L.T. employs ver-  presentation and requires immediate, verbal r e c a l l .  Two  forms are available. Form B was used i n the present study, as follows: Stimulus  Response  flower  spark  table  river  bottle  comb  The subject i s t o l d : "I am going to read you a l i s t of words, two words at a time.  I want you to l i s t e n carefully to  the l i s t of words, because a f t e r I f i n i s h reading i t to you I s h a l l expect you to remember the words that go together.  For  example, i f I should say the words 'East...West* (Pause, ' G-old... S i l v e r , then when I say the word 'East' I ' l l want you 1  to answer 'West', and when I say the word 'Gold' you would, of course, answer (pause)...  'Silver'.  Do you understand?  Now l i s t e n c a r e f u l l y to the words as I read the l i s t to you." The examiner presents the l i s t of paired associates, allowing about a five-second i n t e r v a l between each of the pairs on the l i s t .  Following the i n i t i a l presentation of the l i s t ,  another five-second i n t e r v a l i s allowed, then the examiner presents the stimulus words (flower, table, bottle) one by one i n random order, asking, f o r example, "What went with the word 'table'?"  The subject i s allowed approximately ten seconds  to respond; i f he gives the correct response, he i s told "That's r i g h t " ; however, i f h i s answer i s incorrect, he i s t o l d " No, i t i s . . . (the examiner supplying the correct associate). I f the subject cannot respond within the ten seconds, the correct response i s provided by the examiner. The material i s presented, at random, ip. t h i s way  until  the subject achieves three consecutive, correct responses f o r each of the stimulus words, or .until each stimulus word has been presented t h i r t y times, whichever i s sooner.  The examiner  stops presenting each stimulus word as soon as i t s c r i t e r i o n i s reached.  For example, i f the pair 'table...river'were  learned to the c r i t e r i o n of three consecutive correct associations before the other two pairs, then the stimulus word 'table* would be dropped out of the presentation, with the remaining stimulus words ('flower' and  'bottle') being a l t e r -  nated u n t i l the learning c r i t e r i o n i s reached for each pair or u n t i l they have each been presented t h i r t y times. The score on the P.A.L.T. i s the sum of the number of times the stimulus words have to be presented before the c r i terion i s reached f o r a l l three pairs.  The minimum (best)  score possible would be three: the maximum (worst), 93» The cut-off scores of 30 and 60 were selected on the  - 27 basis of previous studies (Caird et a l , 1962; Inglis, 1959A). Binaural Stimulation*  The administration of the binaural  d i g i t s was accomplished by using a "Roberts 997" stereophonic tape-recorder which played the d i g i t s simultaneously into a set of Koss (Model S - P3) earphones.  The d i g i t s were recor-  ded on the l e f t and right channels, respectively, by the examiner, as outlined i n the Appendix.  They were presented to  the subject at the rate of one pair per two-thirds second. Each subject was instructed as follows: "You are going to hear a number. hear i t i n . "  T e l l me what you hear and which ear you  The d i g i t  '7' was then played on Channel 1. I f  the subject was able to correctly reproduce t h i s d i g i t , then the instructions were repeated with the d i g i t 2.  '2' on Channel  I f the subject reported the wrong number(s), or f a i l e d  to respond to either channel, the volume controls were adjusted u n t i l the correct response occurred f o r each channel.  The  subject was then informed, "You aoe;going to hear two numbers at exactly the same time, one i n each ear. hear."  T e l l me what you  The d i g i t s '7' and '2* were played simultaneously,  the former on Channel 1 acdthe l a t t e r on Channel 2.  I f the  subject correctly reproduced the d i g i t s , disregarding the order of r e c a l l , then the test series was begun.  I f either an  incorrect or no response was given by the subject, the twod i g i t , simultaneous presentation was presented a: second time only. These t r i a l s were designed to provide both a practice  - 28 run and an auditory acuity test so that individual differences i n sensory acuity could be allowed f o r by adjusting the stimulus volume controls. At t h i s point i t may be useful to c l a r i f y some of the t e r minology applied to the binaural s i t u a t i o n . set'  A ' f u l l span or  of binaural d i g i t s consists of a l l the d i g i t s played to  both ears simultaneously.  For example, 5-1-2-4 ( l e f t ) plus  9-8-3-6 (right) would be considered a f u l l set.  A 'half-span'  or 'half-set', therefore, would be a l l those numbers played to either ear simultaneously; for example, 5-1-2-4 ( l e f t ) . One ' t r i a l  1  i s considered to be the playing and attempted r e -  production of a f u l l set of d i g i t s , regardless of the number of d i g i t s comprising the particular f u l l set.  Both 5-1-2-4  plus 9-8-3-6 and 2-1 plus 8-3 would be termed ' t r i a l s ' , one with an eight-digit f u l l set, the other with a four d i g i t set.  full  A test 'series' i s composed of four t r i a l s , each em-  ploying different d i g i t arrangements, at any of the f u l l set d i g i t l e v e l s (that i s , at the 2, 4, 6, or 8 d i g i t l e v e l ) .  No  d i g i t recurred within a given f u l l set. For the actual test series, each subject was told that he must t r y to r e c a l l a l l the numbers from one ear (half-span) before r e c a l l i n g those from the other ear.  The ear to be r e -  called f i r s t by the subject was chosen randomly, using a table of random numbers, by; the experimenter before the study commenced, so that the order of half-span r e c a l l s was prescribed for  a l l subjects f o r each t r i a l .  The randomization  of r e c a l l  - 29 order can also be found i n the Appendix.  A l l subjects r e -  ceived the same randomized prescriptions, but h a l f of the experimental group and h a l f of the control group were told before the  presentation of each t r i a l which ear they were to report  first. the  The other halves of the two groups were t o l d after  presentation of each set of d i g i t s which ear they were  to report f i r s t .  The request to r e c a l l a particular ear (Half-  span or channel) f i r s t was made by the experimenter pointing to a large sign on which was printed "LEFT EAR FIRST" (on the subject's left-hand side) and "RIGHT EAR FIRST" (on the subject's right-hand side). The experimental and control groups were thus divided into subgroups f o r the application of the two experimental cond i t i o n s : the "k" (known) condition, where order of half-span r e c a l l was known to the subject before the presentation of each t r i a l ; the "a" (ambiguous) condition, where the order of r e c a l l was made known to the subject a f t e r the stimuli were presented each time. perimental known), E known), and C  The four groups are designated a  (ex-  (experimental ambiguous), C^. (control  (control ambiguous).  An attempt was made to  cl  match these subgroups i n terms of age, Verbal Scale  (W.A.I.S.)  I.Q., d i g i t span forward performance on the W.A.I.S., and, within the experimental and control groups, to approximate the  subgroups f o r P.A.L.T. performance. At  the beginning of each t r i a l , the subject was t o l d :  "You are going to hear (N) numbers, (N/2) i n each ear.  Listen  - 30 carefully."  -  Then, i f the s u b j e c t happened t o be a member o f  one o f the "k" subgroups, he was  t o l d : " I want you t o t e l l  me  a l l the numbers you heard i n your (x) ear b e f o r e you t e l l  me  the ones you heard i n your (y) ear ( w i t h the experimenter  point  i n g t o the a p p r o p r i a t e s i g n i n f r o n t o f the s u b j e c t ) . " I f the s u b j e c t was  a member o f the "a" c o n d i t i o n , he was  given  the same d i r e c t i o n s , but a f t e r each b i n a u r a l p r e s e n t a t i o n . The b i n a u r a l performance was s c o r e d i n the f o l l o w i n g One  way.  p o i n t was g i v e n f o r each c o r r e c t l y - p o s i t i o n e d d i g i t i n the  h a l f - s e t reproduced  by the s u b j e c t .  The average number o f  c o r r e c t l y - p o s i t i o n e d d i g i t s a t any g i v e n l e v e l was  obtained  by d i v i d i n g the h a l f - s e t t o t a l by 4, the number o f t r i a l s w i t h i n each l e v e l o f d i g i t s .  The example found i n the Appen-  d i x should c l a r i f y the s c o r i n g system used. R e s u l t s and D i s c u s s i o n The means, standard d e v i a t i o n s , and the s i g n i f i c a n c e o f the d i f f e r e n c e s between the means o f the e x p e r i m e n t a l , and t r o l groups i n terms o f age, W.A.I.S. V e r b a l S c a l e  con-  I.Q.,  d i g i t span f o r w a r d performance, and P.A.L.T. s c o r e are shown i n Table 1.  The d i f f e r e n c e between the means was  u s i n g Student's t - t e c h n i q u e (Ferguson,  e v a l u a t e d by  1959)  From Table 1 i t can be seen t h a t the two main groups were not s i g n i f i c a n t l y d i f f e r e n t i n age, W.A.I.S., V e r b a l S c a l e I.Q.,  o r d i g i t span f o r w a r d performance.  They were, o f c o u r s e ,  - 31 s t a t i s t i c a l l y different at a high l e v e l of significance i n mean P.A.L.T. scores.  Tables 2, 4, 6 and 8 summarize the  matching c r i t e r i a f o r each of the four subgroups.  Again, there  were no s i g n i f i c a n t differences found except i n the case of the P.A.L.T.  - 32 -  Table 1 Means, Standard Deviations and the Significance of the Differences Between the Means of the Experimental and Control Groups on the Matching C r i t e r i a  Variable  Age W  i Q A  Experimental Group (N = 20)  Control Group (N = 20)  Between Group Differences  m  m  ^  t  77.90  3.80  <[_  77.85 1 , 3 ,  V  e  r  b  a  l  Digit span f o r ward P.A.L.T. score  91.75 5  >  4  Q  77.45  4.15 12.13 1  >  2  Q  10.15  97.05 5  #  6  5  16.15  0.04  8.11 Q  >  9  5  p  1.53 0  7.46  >  ?  6  20.64  N.S. N.S. N # s >  <.001  - 33 Table 3 presents the comparison between the experimental and control groups i n terms of binaural performance where the instruction f o r r e c a l l order was presented before the d i g i t s were administered.  In the tables, the word " F i r s t " indicates  that t h i s was the ear or channel recalled f i r s t ; "Second" r e fers to the ear or channel recalled  second.  As can be seen from Table 3» the results are not entirel y i n l i n e with the o r i g i n a l hypothesis.  There were no s i g -  n i f i c a n t differences between the performance of the two groups on the channel recalled f i r s t .  This was as expected.  However,  of the differences between the groups f o r the channel recalled second, only that f o r series length one reached an acceptable l e v e l of significance ( <.05).  The differences f o r series  lengths two and four approached this l e v e l ; <.07 spectively.  and 41.08 re-  Series length three was i n the predicted d i r e c -  tion. The lack of s i g n i f i c a n t differences f o r the channel r e called second was not only counter to expectation but s u r p r i sing i n the l i g h t of previous findihgs (Caird and I n g l i s , 1961; Inglis and Sanderson, 1961).  There are a number of  p o s s i b i l i t i e s which might account f o r these r e s u l t s .  In the  present study there i s considerably more v a r i a b i l i t y i n performance f o r both groups than i n the two previously reported investigations.  This, i t i s suggested, may be due to the  difference i n procedure.  In previous studies the patient was  free to r e c a l l either the l e f t or right channel f i r s t .  In the  present investigation he was told which channel to r e c a l l  - 34 first.  It has been suggested (Kimura, 1961)  that e f f i c i e n c y  of r e c a l l i s not the same f o r both ears and i t i s known that i n a binaural stimulation s i t u a t i o n , where order of r e c a l l i s not prescribed, subjects tend to favor one ear or the other.  That i s , i n free r e c a l l , they tend to report one or  the other ear f i r s t f a i r l y consistently.  In the present study,  where channel recalled f i r s t was prescribed, t h i s could result i n the f a i r l y large standard deviations found and  the  concomitant reduction i n significance. The fact that the N i n t h i s investigation was work to t h i s end.  comparatively  small would also  There are other factors such as differences  i n age and i n d i g i t span forward between the present groups and those used i n e a r l i e r studies which could a f f e c t the results.  However, i t seems l i k e l y that the main cause i s  the difference i n experimental design. Where the r e c a l l order was  specified after presentation  of the d i g i t s (the ?a" condition), the r e s u l t s , as shown i n Table 5, are again ambiguous.  For series length one  the  f i r s t channel i s s i g n i f i c a n t and f o r series length two second channel i s s i g n i f i c a n t .  the  The f i r s t channel f o r series  length three i s s i g n i f i c a n t at the ten per cent l e v e l . It was  predicted that the control group would perform  s i g n i f i c a n t l y better than the memory-disordered group on both channels f o r a l l lengths of s e r i e s .  They actually did  perform better but s i g n i f i c a n t l y so only on the series mentioned above.  Having to hold both half-sets i n storage u n t i l  - 35 Table 2 Means, Standard Deviations, and the Significance of the Differences Between the E^. and C" Groups on the Matching C r i t e r i a k  Variable  E, (N=10) K  6  m  C, (N=10) * m  Between Group Differences t P  Age  78.80  4.02  77.50  3.44  0.74  N.S.  W.A.I.S. Verbal I.Q. Digit span forward P.A.L.T.  91.30  9.01  96.80  9.03  5.70  0.90  0.89  N.S. N.S.  76.30  9.34  5.20 15.30  1.29 1.20 16.40  6.13  < .001  Table 2 Means, Standard Deviations, and the Significance of the Differences Between the E, and C, Groups on the Binaural Digit Task No. of Digits  Recall Channel  \  (N=10)  m  cT  C  k  (N=10)  m  Between Group Differences t p  1.  First Second  0.65 0.45  0.38 0.33  0.80 0.80  0.29 0.16  1.006 3.070  N.S. <.01*  2.  First Second  1.02 0.35  0.36 0.56  1.18 0.82  0.46 0.71  0.810 1.678  N.S. <.07*  3.  First Second  1.48 0.48  0.51 0.84  1.78 0.85  0.74 0.71  1.060 1.080  N.S. N.S."  4.  First Second  2.18 0.18  1.02 0.24  2.08 0.68  0.99 1.06  0.222 1.453  N.S. <.08*  * 1 - t a i l test  the order of r e c a l l was prescribed, adversely affected both groups.  The only reasonable explanation f o r these findings  i s that the task was simply too d i f f i c u l t f o r the control group as well as the experimental group.  I t should be kept i n mind  that while the control group was not "memory-disordered" i n the way i n which the experimental group was memory-disordered, the advanced age of the subjects certainly precluded t h e i r having a 'good' memory.  I t has been demonstrated  Caird, 1963B) that performance  (Inglis and  on a binaural memory task i s  d i r e c t l y related to age. It i s at i t s peak about the midtwenties and declines steadily thereafter.  At age seventy,  even i n non-hospitalized, normal subjects, performance  i s ex-  ceedingly poor. While the results shown i n Table 3 and 5 are at least ambiguous and do not support the hypothesis to any great degree, t h i s i s not the case where comparisons  are made of the perfor-  mance of the c r i t e r i o n groups f o r the two procedures.  I t can  be seen i n Table 7, where the experimental group i s compared on performance  f o r the known and ambiguous procedures, that  there are s i g n i f i c a n t differences f o r a l l series lengths f o r the channel recalled f i r s t .  In the case where the patients  knew before-hand which channel they would be required to r e c a l l f i r s t , they d i d s i g n i f i c a n t l y better than when they did not have t h i s information. The same thing did not occur f o r the channel recalled second.  Here, only series length four was found to be s i g n i f i c a n t .  - 37 Table ± Means, Standard Deviations, and the Significance of the Differences Between the E and C Groups on the Matching C r i t e r i a Variable  E  a  (N=10)  C  a  (N=10)  m  m  ^  Between Group Differences t p  Age  76.90  4.06  78.30  4.10  0.73  N.S.  W.A.I.S. Verbal I.Q.  92.20  14.65  97.30  7.06  0.94  N.S.  Digit span f o r ward  5.10  1.52  6.10  1.04  1.60  N.S.  78.60  10.50  17.00  8.50  13.69  < .001  P.A.L.T. score  Table £ Means, Standard Deviations, and the Significance of the Differences Between the E and C Groups on the Binaural Digit Task No. of Digits  Recall Channel  E m  (N=10) /  C  (N=10)  m  6  Between Group Differences t p  1.  First Second  0.40 0.50  0.18 0.26  0.80 0.55  0.31 0.26  3.636 0.438  2.  First Second  0.68 0.23  0.36 0.22  0.88 0.62  0.53 0.44  1.000 N.S. 2.580 <.01  3.  First Second  0.83 0.30  0.50 0.37  1.25 0.50  0.87 0.58  1.340 <.10 N.S. 0.921  4.  First Second  1.20 0.53  0.76 0.51  1.53 0.80  0.53 0.83  1.109 0.896  1 - t a i l test  < .mi  N.S.  N.S. N.S.  - 38 Probably the most reasonable explanation for lack of significance i n the other series i s that the performance of both groups was, f i r s t of a l l v i r t u a l l y minimal, and secondly, extremely v a r i a ble. Table 9 summarizes the between-condition comparisons f o r the  control group.  As can be seen, there are no s i g n i f i c a n t  differences between the known and ambiguous conditions with the  exception of the second channel f o r series length one.  The control subjects were generally able to r e c a l l with equal f a c i l i t y under both conditions.  That i s , not knowing u n t i l  after presentation of the d i g i t s which channel they would be called upon to reproduce f i r s t , did not s i g n i f i c a n t l y impair t h e i r performance. Regarding s e r i a l order effect within each of the four subgroups, i t w i l l be recalled that under the"known" condition s e r i a l order effect was expected, whereas under the "ambiguous" condition i t was not.  The results of these comparisons can  be found i n Table 10, which shows each subgroup's mean d i f f e r ence score between f i r s t and second half-span recalled at each d i g i t l e v e l , the standard deviations of the different scores, and the significance of the mean difference scores.  I t can  be readily observed that the s e r i a l order effect hypotheses are generally confirmed.  The only s t r i k i n g f a i l u r e i s i n the  results of the experimental group under the ambiguous condition, which unexpectedly did display a s e r i a l order effect i n r e production of the binaural d i g i t s .  No adequate explanation  - 39 Table 6 Means, Standard Deviations, and the Significance of the Differences Between the E, and E Groups on the Matching C r i t e r i a Variable  E, (N=10)  E  (N=10)  Between Group Differences t p  a  d  m Age  m  78.80  4.02  76.90  4.06  1.00  N.S.  W.A.I.S. Verbal I.Q. 91.30  9.01  92.20 14.65  0.16  N.S.  Digit span forward  5.70  0.90  1.52  1.00  N.S.  76.30  9.34  78.60 10.50  0.55  N.S.  P.A.L.T. score  5.10  Table 2 Means, Standard Deviations, and the Significance of the Differences Between the E and E Groups on the Binaural Digit Task fc  No. of Digits  Recall Channel  \  (N=10)  m  cf  a m  E  &  (N=10)  €  Between Group Differences t p  1.  First Second  0.65 0.45  0.38 0.33  0.40 0.50  0.18 0.26  1.908 0.381  <.05 N.S.  2.  First Second  1.02 0.35  0.36 0.56  0.68 0.23  0.36 0.22  2.215 0.694  <.05 N.S.  3.  First Second  1.48 0.48  0.51 0.84  0.83 0.30  0.50 0.37  2.876 0.607  <.01 N.S.  4.  First Second  2.18 0.18  1.02 0.24  1.20 0.53  0.76 0.51  2.419 1.988  <.05 <.05  1 - t a i l test  Table 8 Means, Standard Deviations, and the Significance of the Differences Between the and C Groups on the Matching C r i t e r i a Variable  C  k  (11=10)  er  m  C  (N=10) <r  m  Between Group Differences t  77.50  3.44  78.30  4.10  0.45  N.S.  W.A.I.S. Verbal I.Q.96.80  9.03  97.30  7.06  N.S.  Digit span forward  5.20  0.89  6.10  15.30  6.13  17.00  1.04 8.50  0.13 1.90 0.49  N.S.  Age  P.A.L.T. score  N.S.  Table 9_ Means, Standard Deviations, and the Significance of the Differences Between the C, and C Groups on the Binaural Digit Task No. of Digits  Recall Channel  C\, (N=10)  C  a  (N=10)  m  m  cr  cr  a  Between Group Differences t _  1.  First Second  0.80 0.80  0.29 0.16  0.80 0.55  0.31 0.26  2.631  N.S. <.02  2.  First Second  1.18 0.82  0.46 0.71  0.88 0.62  0.53 0.44  1.357 0.760  N.S. N.S.  3.  First Second  1.78 0.85  0.74 0.71  1.25 0.50  0.87 0.58  1.462 1.215  N.S. N.S.  4.  First Second  2.08 0.68  0.99 1.06  1.53 0.80  0.53 0.83  1.553 0.297  N.S. N.S.  - 41 for t h i s finding can he provided at t h i s time. In conclusion, i t would appear that under the "known" short-term memory condition, information probably goes straight into the p-system (Broadbent, 1957;  Caird and I n g l i s ,  196l) with excess information being retained i n the s-system u n t i l i t can be processed.  This poses a serious problem f o r  persons who have defects i n short-term storage, since the information stored i n the s-system i s rapidly 'lost' for r e c a l l . In the ambiguous binaural situation, however, the i n f o r mation l i k e l y a l l goes into storage (inthe s-system) u n t i l i t becomes known which channel i s to be recalled f i r s t , whereupon the appropriate information enters the p-system immediately p r i o r to r e c a l l .  This situation makes complete r e c a l l even  more d i f f i c u l t than i n the "known" situation.  Both memory-  disordered and non-memory-disordered, elderly, psychiatric patients find t h e i r r e c a l l a b i l i t y taxed to the l i m i t .  The mem-  ory-disordered patient, by v i r t u e of an extremely i n e f f i c i e n t storage system, finds t h i s task especially d i f f i c u l t . Another method of investigation which might cast some l i g h t on the nature of short-term memory dysfunction i s that reported by Hebb (1961) and discussed i n Chapter I I . chapter deals with this i n some d e t a i l .  The next  - 42 Table 10 Mean Difference Scores, Standard Deviations, and Significance of Mean Difference Scores Between F i r s t and Second Channel Recall f o r Each D i g i t Level Within the Four Subgroups Group  N 10  10  10  10  No. of Digits  D  S_ D  t  Significance  1  .200  .128  1.562  2  .208  3.245  -< .01  3  .675 1.000  .201  4.975  ^ .001  4  2.000  .296  6.757  < .001  1  -.100 .450  3 4  .525 .675  .233  -1.075 3.041 2.549 2.897  N.S.  2  .093 .148 .206  1  .000  .091  2  .350  3 4  .925 1.400  .163 .134 .296  6.903 4.730  <.05 <.001 <.001  1  .250  .112  2.232  N.S.  2  .250 .750  .179 .190  1.397  N.S. <.01  .725  .399  3 4  N.S.  <.02 <.05 <.02  N.S. 2.147  3.947 1.817  N.S.  - 43 CHAPTER IV Memory Disorder and Cumulative Learning As mentioned i n Chapter I, there i s some evidence that the gross memory d e f i c i t exhibited by some elderly psychiatric patients i s a r e s u l t of a decrease i n the energy of reverberatory a c t i v i t y .  I t was also suggested that Hebb's (1961) method  of repeating d i g i t s would provide a way of testing t h i s notion. To recapitulate, b r i e f l y , Hebb showed that a single presentat i o n of a set of d i g i t s results i n a s t r u c t u r a l trace which i s cumulative with r e p e t i t i o n of the same set of d i g i t s , a l though the r e p e t i t i o n i t s e l f may go unrecognized by the i n d i vidual.  This could be interpreted i n terms of reverberatory  traces and synaptic growth, where the former i s necessary i f the l a t t e r i s to occur. The investigation reported i n t h i s chapter i s concerned with testing a deduction from the hypothesis that memory-disordered patients suffer from a reduction i n the energy of cereb r a l e x c i t a b i l i t y and/or an increase i n the impedance of the supporting neural structures i n the brain.  Both of these  factors may be related to the pathology associated with senile dementia and cerebral a r t e r i o s c l e r o s i s .  I f the a b i l i t y of  these patients to learn a series of repeating d i g i t s by Hebb's method i s depressed, then i t may be reasonable to assume that the energy of the e l e c t r i c a l o s c i l l a t i o n s are reduced to the point where s t r u c t u r a l changes i n the nerve pathways are minimal.  A control group, on the other hand, free of memory  - 44 disorder, should display cumulative learning on t h i s task. Method Subjects The same patients were used i n t h i s study as i n the previous one, with two exceptions; one new patient was substituted i n each of the experimental and control groups.  This was  necessary since the v i s u a l acuity of the two o r i g i n a l patients was not adequate to permit them to participate i n a subsequent task where reasonable v i s i o n was necessary.  Details of the  c r i t e r i o n variables are given i n Table 11. Procedure The procedure used was a r e p l i c a t i o n of Hebb's (1961), mentioned e a r l i e r .  The only differences were that the number  of items was increased to 30 from 24, and the length of each item was reduced to 6 d i g i t s from 9.  Each of the items was  different except that every t h i r d one was repeated. jects were not told of t h i s r e p e t i t i o n .  The sub-  Each item was read  to the subject at the rate of one d i g i t per second with the instructions that he was to r e c a l l them i n the order given. Scores were the number of correct responses f o r the repeated and non-repeated items.  Maximum scores would be 10 f o r the  repeated items and 20 f o r the non-repeated.  The d i g i t series  used w i l l be found i n the Appendix. Results and Discussion The performance of the two groups on t h i s task i s summarized i n Table 12.  When the differences between the means  - 45 of experimental and control groups are compared, the results support the hypothesis,  at least i n d i r e c t l y , that the memory-  disordered patients suffer from a reduction i n the energy of the e l e c t r i c a l o s c i l l a t i o n s and/or an impedance of the neural network.  This, i n Hebb's (1961) terms, mitigates against  "structural modification" based on reverberations.  There i s ,  i n these patients, no evidence of cumulative learning.  This  i s not the case with the control group where cumulative learning did occur.  That i s , the between-group means f o r the re-  peated items are s i g n i f i c a n t l y d i f f e r e n t (P<.05), while the differences for the non-repeated items are not s i g n i f i c a n t . More d i r e c t evidence that the concept of reduced neural e x c i t a b i l i t y i s tenable i s furnished by Obrist et a l (1962). These investigators have shown that elderly patients s u f f e r ing from "brain syndrome" tend to exhibit more diffuse slow wave a c t i v i t y as measured by the EEG than do patients of simil a r age but suffering from "functional" disorders.  They also  demonstrated that EEG changes which are associated with old age are also associated with changes i n i n t e l l e c t u a l functions. S p e c i f i c a l l y , they pointed out that low i n t e l l i g e n c e test scores (W.A.I.S. or Wechsler-Bellevue, Wechsler, 1950,  1945)  are related to slow brain potentials; elderly patients with c l i n i c a l evidence of cerebral a r t e r i o s c l e r o s i s reveal consistently higher correlations between i n t e l l i g e n c e test performance and EEG diffuse slowing than do patients free of t h i s disorder.  - 46 -  Table 11 Means, Standard Deviations, and Significance of the Differences Between Means of the Experimental and Control Groups on the Matching C r i t e r i a Variable  Experimental Group (N = 20) m m  Control Group (N = 20) ot  P  Age  78.00  4.20  77.55  3.64  0.362  N.S,  W.A.I.S. Verbal Scale I.Q. Digit Span Forward Performance  91.35  12.54  96.85  8.14  1.646  N.S.  5.40  1.04  5.65  0.99  0.781  N.S,  77.45  10.27  15.10  7.33  22.109  <.001  Paried-associate learning Test Performance  Table 12 Means, Standard Deviations, and Significance of the Differences Between the Means of the Experimental and Control Groups on the Repeating and Non-repeating Series of Digits Variable  Experimental Group (N = 20) m <j" m  Control Group (N - 20) (S' t P  Repeating Series  4.28  3.61  6.60  3.59  2.667  Non-repeating Series  6.94  5.85  8.65  6.18  0.876  <.05 N.S.  - 47 These findings, i n conjunction with the demonstration by Caird et a l (1963)» that elderly, memory-disordered patients are much more susceptible to the effects of sodium amytal than a control group free of memory disorder, plus the results of the present investigation, lend some weight to the notion of a reduction i n the l e v e l of cerebral e x c i t a b i l i t y as being an important factor i n short-term memory disorder i n some elderly psychiatric patients.  This point of view i s not inconsistent  with that of Gerard (1963) and Obrist et a l (1962).  - 48 CHAPTER V Memory Disorder and S e r i a l Learning The results of the experiments described i n Chapters III and IY are reasonably consistent with previous evidence that at least one abnormality exhibited by some elderly, psychiat r i c patients i s a severe short-term memory dysfunction that t h i s may tory a c t i v i t y .  and  well be due to a decrease i n cerebral reverberaBecause of t h i s reduction, longer-term learning  i s extremely d i f f i c u l t f o r these patients.  While i n general  t h i s i s true, t h i s does not mean that these people are incapable of learning.  ..totally  They can learn a l i m i t e d amount, as  compared with a matched control group, and t h i s i s evidenced by t h e i r performance on the tasks i n the preceding two chapters.  A l l of the procedures used thus f a r have u t i l i z e d r e c a l l  as a measure of learning.  However, i t i s well established  that recognition i s a more sensitive measure; t h i s i s true of normal subjects and probably equally true of memory-disordered psychiatric patients.  The fact that these people cannot  r e c a l l a p a r t i c u l a r stimulus does not necessarily mean that nothing has been learned.  That i s , the a c t i v i t y trace  may  not be "strong" enough to r e s u l t i n r e c a l l but yet be of s u f f i c i e n t strength to allow recognition. The investigation reported i n t h i s chapter was with testing t h i s notion.  It was  concerned  expected that memory-  disordered patients would be i n f e r i o r to a non-memory-disordered control group on both a r e c a l l and recognition task.  Both  - 49 groups would, however, show evidence of learning over a series of t r i a l s on r e c a l l and recognition with the  non-  memory-disordered group displaying the greatest amount of improvement under both conditions. Method Subjects The same patients used i n the experiment reported i n the preceding chapter were again tested. Procedure Bach subject was i n d i v i d u a l l y presented with two l i s t s of ten common words v i a a memory drum. the rate of one per second.  These were presented at  A magnifying glass, attached to  the machine, enlarged the words about threefold. None of the subjects had d i f f i c u l t y i n reading the words.  Each subject  had f i v e t r i a l s on each of the r e c a l l and recognition tasks. The words f o r each l i s t were randomized from t r i a l to t r i a l so that the same order never recurred. w i l l be found i n the Appendix.  The randomized l i s t s  The subjects score on the r e -  c a l l task was the number of words he could correctly r e c a l l , regardless of order, after each t r i a l . In the recognition task the subject was required to corr e c t l y i d e n t i f y the ten stimulus words from a l i s t of twenty words after each t r i a l .  The extraneous or non-stimulus words  on the recognition l i s t were different for each t r i a l .  Half  of each of experimental and control groups did the r e c a l l task f i r s t and the recognition task second.  The reverse  was  - 50 was true for the other h a l f of each group.  The subject's  score on t h i s task was the number of words he could correctly recognize a f t e r each t r i a l , minus those he incorrectly ident i f i e d as being the stimulus words. Results and Discussion The relevant data f o r t r i a l s 1 and 5 for experimental and control groups on the r e c a l l and recognition tasks are shown i n Table 13.  As can be seen, a l l of the differences be-  tween the group means on this i n i t i a l analysis are highly s i g n i f i c a n t , although the performance of both groups on r e c a l l for  t r i a l 1 i s poor.  This may probably be explained f i r s t ,  by the novelty of the procedure for these patients, particul a r l y as t h i s i s related to the perception and comprehension of the v i s u a l l y presented material, and second, by the fact that rate of learning decreases with advancing age  (Bromley,  1958; Gilbert, 1941) and i s greatly impaired where senile dementia and cerebral a r t e r i o s c l e r o s i s are present (Botwinick and Birren, 1951;  Wylie, 1930).  As indicated by the results, both groups improved from t r i a l 1 to t r i a l 5 under both conditions, with the control group manifesting the greatest amount of gain.  This can be  better seen i n Table 14 where a comparison i s made between t r i a l s 1 and 5 on r e c a l l and recognition andi between r e c a l l and recognition f o r f i r s t and f i f t h t r i a l f o r the memorydisordered group. control group.  Table 15 presents the same data f o r the  - 51 Table Means, Standard Deviations, and Significance of the Differences Between the Means of the Experimental and Control Groups on the Recall and Recognition Tasks. T r i a l s 1 and 5 Task  Experimental Group (N = 20) m cr  Control Group (N = 20) t <f  m  P  Recall  trial 1  1.30  1.25  2.85  1.27  3.875 <.001  Recall  trial 5  3.00  1.48  5.95  1.14  7.024 <.001  Recognition  trial 1  2.55  1.55  5.40  3.23  3.567 <.01  Recognition  trial 5  3.68  2.82  7.98  2.78  4.831 <.001  Table 14 Means, Standard Deviations, and Significance of the Differences Between the Means on T r i a l s 1 and 5 of the Recall and Recognition Tasks f o r the Experimental Group Task and T r i a l Comparison (A) vs (B)  (A)  (B)  m  cr  m  cr  t  P  Recall 1st Recall 5th  1.30  1.25  3.00  1.48  3.864 <.001  RecogRecogn i t i o n 1st h i t i o n 5th  2.55  1.55  3.68  2.82  1.569  Recall 1st ^ c o g - ^ Recall 5th ^ecog-  1  3  >  3  Q  1  #  2  >  Q  0  1  >  4  5  8  2  ^ ^  6  8  2  ^  Q 2  2  ^  7  Q  t  5  9  Q  1  <  >  0  N.S. 1  N # s >  - 52 In Table 14 i t can readily be observed that the performance of the experimental group on the r e c a l l task improved cantly from the f i r s t to f i f t h t r i a l .  signifi-  That i s , there was a  small but s i g n i f i c a n t indication of learning.  On the other  hand, performance on the recognition task did not s i g n i f i c a n t l y improve over the f i v e t r i a l s .  Furthermore, while the memory-  disordered patients were better able to recognize then r e c a l l the  correct words on the f i r s t t r i a l , t h i s was not the case f o r  the  f i f t h t r i a l where there was no s i g n i f i c a n t difference be-  tween the two procedures.  It appears as i f the experimental  group reached a peak of performance beyond which i t could not go, at least with f i v e learning t r i a l s . the  That i s , by the end of  f i f t h t r i a l the patients i n t h i s group were performing l i t t l e  better on recognition than r e c a l l .  From this set of results  i t i s suggested that the memory-disordered patients can remember  a negligible amount of stimulus material; they have a  limited capacity, beyond which additional stimuli leave l i t t l e or no trace which can be u t i l i z e d i n successfully selecting the  correct word from a number of alternatives. A somewhat different state of a f f a i r s i s evidence from  Table 15, where the same analyses were done f o r the control group.  It can be seen that the performance of t h i s group did  improve s i g n i f i c a n t l y from the f i r s t to f i f t h t r i a l s on both r e c a l l and recognition.  Furthermore, performance was  signifi-  cantly superior on the recognition task f o r both f i r s t and  fifth  - 53 Table 1£ Means, Standard Deviations, and the Significance of the Differences Between the Means on T r i a l s 1 and 5 of the Recall and Recognition Tasks f o r the Control Group  Task and T r i a l Comparison (A) vs (B)  (A) m  (B) cT  m  t  P  Recall 1st  Recall 5th  2.85  1.27  5.95  1.14  8.158 <.001  Re cog n i t i o n 1st  Recog*~ n i t i o n 5th  5.40  3.23  7.98  2.78  2.716 <.01  Recall 1st  Recogn i t i o n 1st  2.85  1.27  5.40  3.23  3.269 <.01  Recall 5th  Recogn i t i o n 5th  5.95  1.14  7.98  2.78  3.022 <.01  -  - 54 t r i a l s ; on the f i r s t t r i a l they were, on the average, able to r e c a l l f i v e and a h a l f words and on the l a s t t r i a l , eight words of a possible ten. The r e s u l t s of this investigation are congruent with those reported i n chapters I I I and IV. A l l of these findings lend support to the notion that the memory disorder exhibited by some elderly, psychiatric patients may be referable to a r e duction i n cerebral reverberatory a c t i v i t y which renders longer-term learning v i r t u a l l y impossible.  The experiment reported  i n t h i s chapter suggests that there i s a l i m i t to the amount of material which can be learned, under the conditions employed here, by patients suffering from a gross memory disorder. That i s , t h e i r performance rapidly approaches some asymptote. Once they are performing to t h e i r capacity, there i s l i t t l e or no gain i n continuing the learning t r i a l s .  This  suggestion  i s supported by the fact that these patients required, on the average, 76 t r i a l s or presentations to learn three simple paired associates. control group.  Only 15 presentations were required by the  - 55 CHAPTER VI Conclusions The review of the l i t e r a t u r e pertinent to, and outlined i n , the f i r s t two chapters of the present thesis permits the following  generalizations:  (1) There i s i r r e f u t a b l e evidence that a short-term memory d e f i c i t i n some elderly, psychiatric patients actually does e x i s t . (2) There i s reasonable support for the notion that reduced cerebral e x c i t a b i l i t y i s the possible cause of the short-term learning d e f i c i t observed i n these elderly, psychiatric patients. The experimental techniques recently employed by Broadbent (1957) and by Hebb (1961), together with a s e r i a l learning method, are relevant to the study of 'memory function' i n e l derly, psychiatric patients.  The t h i r d , fourth, and f i f t h  chapters of t h i s thesis were concerned with s p e c i f i c i n v e s t i gations (binaural stimulation, cumulative learning, s e r i a l learning with r e c a l l and recognition) which were intended to further examine the relationship between the concept of cereb r a l e x c i t a b i l i t y and short-term memory dysfunction  i n elderly,  psychiatric subjects. The results of the three studies reported i n t h i s thesis lead to certain, legitimate  inferences:  (l) E l d e r l y , psychiatric patients who exhibit c l i n i c a l l y ascertained memory disorder, have considerable d i f -  - 56 f i c u l t y with r e c a l l i n g stimuli presented b i naurally and simultaneously.  They experience  great d i f f i c u l t y i n dealing with the items which must be stored before r e c a l l occurs. This d i f f i c u l t y i s accentuated where the r e c a l l order i s not prescribed for the subjects u n t i l after the stimuli have been presented. These findings lend additional support to the notion that i n these patients there i s a breakdown i n the short-term storage system of the type postulated by Broadbent (1957). (2) The cumulative learning study, involving a repeating series of d i g i t s supplies indirect evidence that the concept of reduced neural excitability  i s tenable as the cause underlying  the short-term storage dysfunction found i n certain elderly patients. (3) Although memory-disordered, elderly, psychiat r i c patients do have considerable d i f f i c u l t y r e c a l l i n g recently-presented stimuli, t h e i r e f f i c i e n c y of reproducing the stimuli i s appreciably increased when these subjects are presented with the stimulus words i n a recogn i t i o n situation.  In other words, the results  from the s e r i a l learning study suggest that at least some learning does occur even where the  - 57 patients exhibit gross memory disorder, but that there appears to be a d e f i n i t e l i m i t to the amount of material which can be learned by these patients. An extension of the present thesis might include an examination of the degree of relationship between performances on such tasks as the binaural stimulation, cumulative learning, and r e c a l l and recognition s e r i a l learning, and the degree of BEG abnormality exhibited by elderly, psychiatric patients with short-term memory dysfunction.  It i s expected that the  experimental subjects, i n contrast to the controls, would d i s play s i g n i f i c a n t l y more diffuse slow waves, i n the delta and theta bands.  Were such a s i g n i f i c a n t relationship found be-  tween these behavioral measures and EEG a c t i v i t y , then one would have more direct evidence than i s presented i n t h i s thes i s that short-term learning d e f i c i t i s associated with, and probably attributable to, a reduction i n cerebral e x c i t a b i l i t y .  - 58 REFERENCES Babcock, H. and Levy, L. Test and manual of directions, the r e vised examination f o r the measurement of e f f i c i e n c y of mental functioning. Chicago: C.H. Stoelting Co., 1940. Barnes, R.H., Busse, E.W., and Freidman, E.L. The psychological functioning of aged individuals with normal and abnormal electroencephalograms: a study of hospitalized i n dividuals. J . nerv. ment. P i s . . 1956, 124, 585-593. Botwinick, J . and Birren, J.E. The measurement of i n t e l l e c t u a l decline i n the senile psychoses. J . consult. Psychol. 1951, 15, 145-150. Broadbent, D.E. Immediate memory and simultaneous s t i m u l i . Quart. J . exp. Psychol.. 1957, 9, 1-11 Broadbent, D.E. Flow of information within the organism. J . verb. Learning verb. Behav, 1963, 2, 34-39. Broadbent, D.E. and Heron, A. Effects of a subsidiary task on performance involving immediate memory by younger and older men. B r i t . J . psychol.. 1962, 53, 189-198. Bromley, D.B. Some effects of age on short-term learning and r e membering. J . Gerontol.. 1958, 13, 398-406. Caird, W.K.  Short-term storage i n the senium: an investigation with special reference to memory disorder i n elderly psychiatric patients. Unpublished doctoral thesis, Queen's University, June, 1962.  Caird, W.K., Personal communication, 1963. Caird, W.K. and I n g l i s , J . The short-term storage of auditory and v i s u a l two channel d i g i t s by elderly patients with memory disorders. J . ment. S c i . . 1961, 107, 1062-1069 Caird, W.K., Laverty, S.G., and I n g l i s , J . Sedation and sleep threshold i n elderly patients with memory disorder. Gerontologia C l i n i c a , 1963, 5, 55-62 Caird, W.K., Sanderson, R.E., and Inglis J . Cross-validation of a learning test f o r use with elderly psychiatric pat i e n t s . J . ment. S c i . . 1962, 108, 368-370 Dorken, H. and Greenbloom, G.C. Psychological investigation of senile dementia. G e r i a t r i c s . 1953, 8, 324-333  Ferguson, G.A. S t a t i s t i c a l analysis i n psychology and education. Toronto: McGraw-Hill, 1959. Gaito, J . DNA and RNA as memory molecules. 70, 1963, 5, 471-480.  Psychol. Rev.,  Gerard, R.W. The material basis of memory. ing verb. Behav.. 1963, 2, 22-33.  J . verb. Learn-  Gilbert, J.G. Memory loss i n senescence. Psychol. 1941, 36.  J . abnorm. soc.  Glickman, S.E., Perseverative neural processes and consolidat i o n of the memory trace. Psychol. B u l l . . 1961, 58, 218-233. Gomulicki, B.R. The development and present status of the trace theory of memory. B r i t . J . Psychol. Monograph.. 1953, 29. Hebb, D.O. The organization of behavior. 1949.  Hew York: Wiley,  Hebb, D.O. Distinctive features of learning i n the higher a n i mal, i n J.F. Delafresnaye (Ed.) Brain mechanisms and learning. Oxford: Blackwell, 1961. Hunt, E.B. Simulation and analytic models of memory. Learning verb. Behav.. 1963, 2, 49-59.  J . verb.  I n g l i s , J . An experimental study of learning and "memory function" i n elderly psychiatric patients. J . ment. S c i . , 1957, 103, 796-803. I n g l i s , J . Learning, retention and conceptual usage i n elderly patients with memory disorder. J . abnorm. soc. Psychol. 1959B, 59, 210-215. Inglis, J . A* paired associate learning test f o r use with e l derly psychiatric patients. J . ment. S c i . , 1959A, 105, 440-443. I n g l i s , J . and Caird, W.K. Modified d i g i t spans and memory d i s order. P i s , nerv. Syst.. 1963A, 24, 46-50. I n g l i s , J . and Caird, W.K. Age differences i n successive r e sponses to simultaneous stimulation. Canad. J . Psychol. 1963B, 17, 98-105. I n g l i s , J . and Sanderson, R.E. Successive responses to simultaneous stimulation i n elderly patients with memory d i s order. J . abnorm. soc. Psychol.. 1961, 62, 709-711  - 60 Kimura, D. Some effects of temporal-lobe damage on auditory perception. Canad. J. Psychol.. 1961, 15, 156-165 K r a i , V.A. Senescent forgetfulness; benign and malignant. Canad. med. Assoc. J . . 1962, 86, 257-260. K r a i , V.A. and Durost, H.B. A comparative study of the amnestic syndrome i n various organic conditions. Amer. J. Psychiat.. 1953, 110, 41-47. Liberson, W.T. and Seguin, G.A. Brain waves and c l i n i c a l features i n a r t e r i o s c l e r o t i c and senile mental pat i e n t s . Psychosom. Med.. 1945, 7, 30-35. Luce, R.A. and Rothschild, D. The correlation of electroencephalograph^ and c l i n i c a l observations i n psychiat r i c patients over 65. J . Gerontol.. 1953» 8, 167172. McCulloch, W.S. Why the mind i s i n the head, i n L.A. Jeffress (Ed.) Cerebral mechanisms i n behavior. New York: Wiley, 1951. Melton, A.W. Implications of short-term memory f o r a general theory of memory. J . verb. Learning verb. Behav.. 1963, 2, 1-21. Milner, P.M. Learning i n neural systems, i n M.C. Yovits and S. Campbell (Eds.) Self-organizing systems. Oxford. Pergamon Press, I960. Milner, P.M. A neural mechanism for the immediate r e c a l l of sequences. Reprint from Kybernetik, July, 1961, 76-81. Mundy-Castle, A.C., Hurst, L.A., Beerstecher, D.M., and Prinsloo, T. The electroencephalogram i n the senile psychosis. Blectroencephalog. and c l i n . Neurophysiol. 1954, 6, 245-252. Obrist, W.D., Busse, E.W., Eisdorfer, C , and Kleemeier, R.W. Relation of the electroencephalogram to i n t e l l e c t u a l function i n senescence. J . Gerontol.. 1962, 17, 197-206. Obrist, W.D. and Henry, C.E. Electroencephalographic findings i n aged psychiatric patients. J . nerv. ment. P i s . . 1958, 126, 254-267. Pauling, L. A molecular theory of general anesthesia. 1961, 134, 1-7.  Science  - 61 Shagass, C , and Naiman, J . The sedation threshold as an objective index of manifest anxiety i n psychoneurosis. J. Psychosom. Res.. 1956, 1, 49-57. Wechsler, D. Manual of the Wechsler Adult Intelligence Scale. New York: Psychol. Corp., 1955. Weinstein, E.A., Kahn, R.L., Sugarman, L.A., and Linn, L. The diagnostic use of amobarbital sodium ("amytal sodium") i n brain disease. Amer. J . Psychiat., 1953» 109, 889-894. Welford, A.T. Age and learning: theory and needed research. In Experientia Supplementum IV. Symposium on experimental gerontology. Sasel: Birhauser Verlag, 1956, 136-144. Wimer, R.E. A supplementary report on age differences i n r e tention over a twenty-four hour period. J . Gerontol., I960, 15, 417-418. Wylie, M. An experimental study of recognition and r e c a l l i n abnormal mental cases. Psychol. Monogr.. 1930, 13. Yntema, D.B. and Trask, P.P. Recall as a search process. verb. Learning verb. Behav.. 1963, 2, 65-74.  J.  -  62  -  APPEND.  - 63 -  Digits used f o r Binaural Stimulation Channel 1 ( l e f t ear) Practice) 7 Series ( Blank ) 7  Test Series  Channel 2 (right ear) Blank 2 2  Randomization pattern: 'Ear' (£-set) requested to r e c a l l f i r s t  _  5  1  left  9  6  right  6  3  left  4  7  left  21  83  right  97  54  right  26  38  left  47  85  left  547  396  right  321  758  left  469  132  left  658  243  left  5124  9836  right  3752  1486  left  1298  7364  left  7316  5249  right  - 64 An Example of the Scoring System Used for Binaural Digit Performance The Correct Order of Recall F i r s t 4—span  Second 4--span  (Trial l )  396  547  ( T r i a l 2)  321  758  ( T r i a l 3)  469  132  ( T r i a l 4)  658  243  F i r s t -jr-span  Second 4—span  the 6-digit l e v e l or full-set  An Obtained Order of Recall  596  nil  321  798  469  32-  258  653  2  0  3  2  3  0  2  1  10  3  Score f o r the Obtained Recall  avg: 10 = 4  2.50  I  4  = 0.75  - 65 Digits Used f o r the 'Repeating Series' Experiment 1. 2.  912683 594821  * 3. 4.  612794 521948  5. * 6.  452831  7. 8. * 9. 10. 11. * 12. 13. 14. * 15.  16.  683924  17. *18.  783649  19. 20.  361274  612794 852197  612794 781932  *21. 22.  612794 627918  427391  23.  429851  612794  *24.  679815  25. 26.  612794 856192  486153 612794 514296 265314 612794  *The repeating series of d i g i t s .  *27. 28.  648973 612794 385162  29. *30.  439175 612794  -  66  -  Words Used f o r the Recall and Recognition Tasks Recall Stimuli  Recognition Stimuli  Extraneous Stimuli on Recognition Lists  cigar  wrist  butter  gloom  voter  tub  cover  legion  yarn  camel  torch  toad  orphan  bake  sermon  daddy-  jungle  bucket  chorus  runner  ham  marsh  circus  ladder  bunny-  apron  trout  hip  famine  lantern  

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