Priming of spatial configurations in alcoholic Korsakoff's amnesia

BRAIN AND COGNITION 18, 34-45 (1992)

Priming of Spatial Configurations in Alcoholic Korsakoff’s Amnesia

MIEKE VERFAELLIE, WILLIAM P. MILBERG, LAIRD S. CERMAK, AND LYNN L. LETOURNEAU

Memory Disorders Research Center, Boston University School of Medicine and Boston Veterans Administration Medical Center

To examine priming for novel, nonverbal patterns, a modification of the par- adigm used by Gabrieli et al. (1990, Neuropsychologia, 28, 417-427) was administered to a group of Korsakoff patients, a group of alcoholic controls, and a group of normal controls. Subjects were asked to connect five-dot configurations into the first pattern that came to mind. Priming was than assessed by having the subjects copy experimenter-provided interpretations for each configuration and examining the effect of this manipulation on the subjects’ subsequent interpretation of the same configurations. For the Korsakoff patients, the copied prime replaced their initial perceptual interpretation less frequently than it did for normal controls. Instead, the prime had its effect by combining with the baseline percept. These findings suggest that priming for novel, nonverbal material is weaker and less direct for Korsakoff patients than it is for controls. o 1~2 Academic press, 1nc.

Performance on implicit memory tasks has become an increasingly im- portant topic for investigators of the amnesic syndrome, because it has provided a window on the preserved learning abilities of memory-impaired patients. Using a variety of experimental paradigms, it has now been demonstrated that exposure to new information can influence the amnesic’s performance on a subsequent task, despite a complete inability on the patient’s part to remember the previously presented information.

This indirect effect of a learning episode has been attributed to some form of unaware or implicit memory for previous episodes (e.g., Jacoby,

The authors thank Rus Bauer for his valuable comments on an earlier draft of this paper. This research was supported by NlNCDS Program Project Grant NS26985 and NIAAA Grant AA-00187 to Boston University School of Medicine and by the Medical Research Service of the Veterans Administration. Please address correspondence and reprint requests to Dr. Mieke Verfaellie, Memory Disorders Research Center (116B). VA Medical Center, 150 S. Huntington Avenue, Boston, MA 02130.

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0278-2626192 $3.00 Copyright 0 1992 by Academtc Press. Inc. All rights of reproduction in any form reserved.

PRIMING OF SPATIAL CONFIGURATIONS 35

1983; Roediger & Blaxton, 1987) or to activation of information already represented in memory (Cermak, Talbot, Chandler, & Wolbarst, 1985; Graf & Mandler, 1984). So far, it has been difficult to choose between these two explanations because most tasks have used verbal stimuli, which have a preexisting representation in memory. One way of circumventing this problem has been to use pseudowords, which do not have a preexisting lexical representation. In at least one study (Cermak et al., 1985), Kor- sakoff patients failed to show repetition priming for pseudowords. How- ever, even when pseudowords are used, an activation account cannot be ruled out since it can be argued that nonwords contact “sublexical,” phonological or orthographic units (McClelland & Rumelhart, 1981; Ben- tin, 1989). To circumvent this difficulty, stimuli that do not have preexisting “unitized” representations need to be employed. If these stimuli can prime performance on a subsequent task, then the hypothesis that their influence is episodic would be supported. Given the patient’s obvious prior history with verbal stimuli, the use of novel, nonverbal stimuli may be most appropriate in studies designed to address this question.

Although there have been demonstrations of priming-like effects using pictures with amnesic patients, these studies have not used stimuli that were unambiguously nonverbal. For example, Warrington and Weiskrantz (1968) demonstrated that Korsakoff patients could identify fragmented pictures more rapidly upon their second presentation and Milner, Corkin, and Teuber (1968) demonstrated a similar effect with H.M. In both studies, the amnesic patients showed less savings than the control subjects, yet significant facilitation was obtained. These results, however, could not be counted as a pure demonstration of priming unmediated by language because the facilitation effect was based on subjects’ naming of highly verbalizable familiar pictures.

To date, priming for completely nonverbalizable material has been studied only once, in the severely amnesic patient H.M. (Gabrieli, Mil- berg, Keane, & Corkin, 1990). This was done using as stimuli a series of five-dot configurations which perceptually could be organized to suggest a variety of figures. Although arguably these figures might share some components with premorbidly established perceptual representations, in every case the subject had to first impose a novel visual analysis on the dot configurations before labeling could occur. H.M. was shown these five-dot configurations and was asked to draw any figure onto each dot pattern by connecting all the dots with straight lines. These figures, based on H.M.‘s interpretation of the dot patterns, served as his baseline com- pletions. In a second session, he was asked to copy target figures which connected the dots onto the dot patterns; these figures served as exper- imentally provided primes. Finally, he was asked to again connect the dots into any pattern that came to mind. Despite an inability to recall

36 VERFAELLIE ET AL.

the copied patterns, H.M. produced as many primed patterns as did controls when re-presented with the dot configurations and asked to draw the first pattern that came to mind.

One shortcoming of this study, however, was that the experimenters did not have a measure of spontaneous change in H.M.‘s performance over time. Consequently, it could not be determined whether his tendency to draw the priming patterns as his final drawing was due to the presentation of primes or due to nonspecific variability in his performance across test sessions. Additionally, the investigators scored as priming only those instances in which the exact reproduction of the prime was elicited and consequently did not consider the possibility that the prime might be incorporated as part of a more complex response. Such blending would reflect a more indirect effect of the prime. In order to correct for these difficulties and to collect data from a larger group of amnesic patients, we administered a task similar to that used by Gabrieli et al. (1990) to a group of Korsakoff patients and controls. In the copy task, we first measured how the subjects spontaneously connected the dots and then asked them to copy prime configurations, chosen to be different from their baseline drawings. To obtain a baseline for spontaneous change, we also administered a control task in which subjects completed the same patterns on two successive occasions, but were not exposed to intervening primes (no copy condition). Finally, we introduced a lenient scoring criterion which allowed us to examine the extent to which patients incorporated the prime in their final drawing. These changes permitted a more detailed picture of perceptual priming.

METHODS

Subjects Three groups of subjects participated in this experiment. The first group consisted of nine

patients with alcoholic Korsakoff syndrome who were residing in various chronic care fa- cilities in Massachusetts and Rhode Island. All had histories of chronic alcoholism, were unable to recall day-to-day events, were disoriented to time and place, and had retrograde amnesias of varying degrees. The patients’ mean age was 64 (range = 53-76) years, with an average of 12 (range = 9-16) years of education. The average WAIS-R VIQ score for this group was 101 (range = S&134), WMS score was 83 (range = 67-112), WMS-R Attention score was 104 (range = 81-117), General Memory score was 66 (range = 50- W), and Delayed Memory score was 57 (range = 50-65).

The second group consisted of 18 chronic alcoholics from inpatient clinics at the Brockton and Boston VAMCs, public halfway houses in the Boston area, and volunteers living in private residences. None of these subjects evidenced any signs of neurological damage or psychiatric illness. All had abstained from alcohol for at least 1 month prior to participation in this experiment. This group’s average age was 59 (range = 49-75) WAIS-R verbal IQ score was 112 (range = 90-128) WMS score was 123 (range = 103-143), and average education was 13 (range = 9-16) years.

The third group contained 18 normal controls, matched as closely as possible to the Korsakoff and alcoholic subjects for age (mean = 66 years; range = 52-76) and education

PRIMING OF SPATIAL CONFIGURATIONS

DOT PATTERN BASELINE PRIME FINAL DRAWING

37

.

. l

.

. .

.

.

’ f F 9 . 1 A n

FIG. 1. Illustrations of the initially provided dot patterns, baseline, prime, and final drawings.

(mean = 14 years; range = 12-20). This group’s average WAIS-R verbal IQ score was 116 (range = 97-146) and WMS score was 124 (range = 100-143). Overall, the groups did not differ in age [F(2, 42) = 3.11 and education [F(2, 42) = 1.571, but did differ in verbal IQ [F(2, 42) = 5.16; p < .05].

Stimuli Subjects were presented with six stimuli, each consisting of configurations of five dots.

These dot configurations were all subsets derived from a common 3 x 3 square matrix and were constructed to be similar to those devised by Garner (1974). Each five-dot configuration was presented on a plain sheet of white paper and could be completed with a series of straight lines to form a number of different figures.

A set of 24 priming stimuli (4 possibilities for each of the 6 original dot configurations) were chosen from a pool of possible patterns most frequently drawn by a sample of 10 young normal controls between the ages of 22 and 25. For each subject, the figure that shared the least number of lines with their baseline drawing was chosen to serve as the priming pattern. Illustrations of a baseline, prime and final drawing are presented in Fig. 1.

Procedure Copy task. During a first session in which baseline data were collected, subjects were

shown six different configurations, one at a time. They were asked to connect the dots using straight lines into the first figure that came to mind. One week later, subjects were asked to copy six designs (the priming figures) onto a grid of nine dots. This was followed by a 3-min distractor task in which subjects were asked to write down as many items found in a supermarket as they could possibly think of. Next, the original six-dot configurations were


readministered and patients were again asked to connect the dots with the first figure that came to mind.

No Copy tusk. During the first session, baseline data were obtained in a manner identical to that in the copy task. Subjects were shown the six master configurations and asked to draw the first figure that came to mind. One week later, this task was repeated in exactly the same format.

The majority of Korsakoff patients participated in both the Copy and the No Copy task, with at least a year separating the two test procedures. Except for two subjects in both the alcoholic and normal control groups, there was no other overlap in the subjects used for the two procedures.

RESULTS

To examine the nature of the subjects’ final dot interpretation in the Copy task, three possible sources of influence on their final performance were considered: influence of the baseline drawing, influence of the prime, and extraneous influences not clearly attributable to either the baseline or the prime. In the No Copy task, only the subjects’ baseline drawing and extraneous influences could affect their final performance. However, to statistically control for the possibility that in the Copy condition, any reference stimulus might somehow be similar to the final drawing, in the No Copy condition, a nonexposed stimulus was selected for each baseline drawing from the pool of possible primes. This was done using the same criteria that guided selection of real primes. The influence of nonexposed reference stimuli in the No Copy condition was then directly compared to the influence of exposed primes in the Copy condition. To evaluate the extent to which each source of influence affected the final dot interpretation, a strict and a lenient scoring criterion were used, which will be discussed separately.

Strict scoring criterion. According to the strict scoring criterion, a source of influence was scored if and only if the final figure was identical to the source in question. For example, when considering the first trial presented in Fig. 1, the influence of the baseline and prime figure on the final drawing would be zero, since the final drawing is not identical to either one. The extraneous influence, in contrast, would receive a score of one, since it was assumed that factors other than the baseline or prime contributed to the final drawing. A similar score would be obtained for the second and third trials presented in the figure. The three sources of influence, referred to as Baseline, Prime, and Extraneous measures, were considered to be separate dependent variables. For each, we compared their effect on the Copy and No Copy task. Summary findings on the percentage of trials on which the final drawing reflected each source of influence are presented in Fig. 2.

A 3 (Group: Korsakoff, Alcoholic, Normal Control) x 2 (Task: Copy, No Copy) ANOVA performed on the percentage of trials influenced by baseline performance, revealed no effect of Group [F(2, 48) = .42; p > .lO] or Task [F(l, 48) = 1.94; p > .lO], but there was a significant Group

PRIMING OF SPATIAL CONFIGURATIONS

BASELINE

100

0 KORS ALC NOR”

PRIYE

39

KORS ALC NORM

EXTRANEOUS

100

KORS ALC WORN

FIG. 2. Sources of influence on the final drawing according to the strict scoring criterion. (W COPY, (B) no copy.

X Task interaction [F(2, 48) = 3.58; p < .05]. The latter effect reflected the fact that for the alcoholics, the baseline drawing contributed significantly more frequently to the final dot interpretation in the No Copy task than in the Copy task [F(l, 48) = 9.21; p < .Ol]. The Korsakoff patients [F(l, 48) = .65; p > .lO] and normal controls [F(l, 48) = .26; p > .lO] showed no difference in the extent to which their baseline performance contributed to their final drawing in these two conditions.

In contrast, analysis of the percentage of trials influenced by priming patterns revealed that the groups did differ in the extent to which they


incorporated the prime into their final target drawing [F(2, 48) = 3.66; p < .05]. Overall, the final dot interpretations of the Korsakoff patients significantly less often matched a preselected priming stimulus (exposed prime or nonexposed reference stimulus) than those of the normal controls. The performance of the alcoholic controls fell in between that of the Korsakoff patients and normal controls, but did not significantly differ from either one. Additionally, a significant effect of Task [F(l, 48) = 9.36; p < .Ol] was obtained, indicating, as expected, that presentation of an exposed prime in the Copy condition affected the subjects’ final performance more than a nonexposed reference stimulus in the No Copy condition. Although the Group X Task interaction was not significant [F(2, 48) = 2.19; p > . lo], simple main effects were performed to test the a priori hypothesis that the Korsakoff patients, relative to the other two groups, would be less affected by the preselected prime in the Copy than in the No Copy task. Results of the analysis confirmed this hypothesis: Korsakoff patients did not differ from the other groups in the No Copy task [F(2, 48) = .57; p > .lO], but were significantly less influenced than the other groups by a prime they had been exposed to in the Copy task [F(2, 48) = 5.28; p < .Ol].

Finally, analysis of the percentage of trials influenced by extraneous factors also revealed a significant Group effect [F(2, 48) = 3.58; p < .05] as well as a significant Group X Task interaction [F(2, 48) = 5.16; p < .Ol]. Overall, the final drawings of the Korsakoff patients more frequently reflected an extraneous influence than did the drawings of either of the other groups. Additionally, the alcoholics tended to show more extraneous influences on the final dot interpretation in the Copy than in the No Copy condition [F(l, 48) = 6.37; p < .lO], whereas the opposite was true for the normal control subjects [F(l, 48) = 3.26; p < .lO].

Lenient scoring criterion. A lenient scoring criterion was also devised in which the effect of the Baseline, Prime, and Extraneous variables was scored if the source in question was incorporated into the final design, irrespective of additional lines that might also be present in the final design. Because a final design might incorporate both the Baseline and Prime, a fourth source of influence, referred to as Baseline + Prime, was also included. Again considering Fig. 1, the final drawing presented in the first trial would receive a positive score for Prime, but not for Baseline, since only the former source was fully incorporated into the final performance. The second trial would receive a positive score for Extraneous influence, whereas the third trial would receive a positive score for Base- line. As with the previous scoring method, each source of influence was analyzed as a separate dependent variable. Summary findings on the percentage of trials on which the final drawing reflects each source of influence are presented in Fig. 3.

Applied to the percentage of final designs influenced by the baseline


KOns ALC *OR”

BASELINE AND PRIME 100, 1

EXTRANEOUS

*one UC NOR”

FIG. 3. Sources of influence on the final drawing according to the lenient scoring cri-

rendition, the more lenient scoring criterion yielded somewhat different results than did the strict criterion. In this case, a significant main effect of Task [F(l, 48) = 5.45; p < .05] was obtained, indicating that across


groups, subjects incorporated their baseline drawing more frequently into their final interpretation in the No Copy task than in the Copy task.

Analysis of the percentage of trials influenced by priming stimuli revealed results similar to those obtained using the strict scoring criterion. For the Korsakoff patients, a preselected prime influenced their final dot interpretations less often than it did for the other groups [F(2, 48) = 3.25; p < .05]. Again, only the difference between the Korsakoff patients and normal controls reached significance, while the performance of the alcoholic controls fell in between that of the other two groups. As expected, real primes to which subjects were exposed in the Copy condition affected performance more than nonexposed reference stimuli in the No Copy condition [F(l, 48) = 9.67; p < .Ol]. Finally, although the Group X Task interaction was not significant [F(2, 48) = 1.96; p > .lO], testing of simple main effects to evaluate the a priori hypothesis described above, again revealed that the groups differed from each other in the Copy condition [F(2, 48) = 4.74; p < .05], but not in the No Copy condition.

Examination of the combined influence of both the Copy and Baseline revealed no effect of Group [F(2, 48) = .21; p > .lO]. There was a trend for the main effect of Task [F(2, 48) = 3.34; p < .lO], indicating that the copy and baseline jointly influenced the final drawing more frequently in the Copy condition (mean = 26.7%) than in the No Copy condition (mean = 12.8%).

Finally, analysis of the percentage of trials influenced by extraneous factors revealed that the groups did not differ in the extent to which they incorporated extraneous features [F(2, 48) = 1.10; p > .lO]. There was a significant effect of Task [F(l, 48) = 4.61; p < .05], which indicated that extraneous sources influenced performance more in the No Copy than in the Copy task. The Group X Task interaction was marginal [F(2, 48) = 2.65; p < .lO]. Tests of simple main effects indicated that the Korsakoff patients were more influenced by extraneous sources in the No Copy than in the Copy condition [F(l, 48) = 5.13; p < .05]. A similar trend was observed in the performance of the normal controls [F(l, 48) = 3.60; p < .lO], but this was not the case for the alcoholics.

DISCUSSION

Copying figures onto dot patterns influenced the final drawings of all groups tested, although each group showed somewhat different patterns of influence. Looking first at the strict scoring (Fig. 2), where only exact replications of previous patterns were scored, all groups showed significant priming, as evidenced by the fact that the prime affected performance in the Copy task more so than in the No Copy task. This means that critical patterns which the subjects had previously copied were more frequently produced than reference stimuli to which they had not been exposed. This effect, however, was quite small for all groups and especially so for


the Korsakoff patients. Indeed, on this measure the Korsakoff patients primed significantly less than did the normal controls.

Although the Korsakoff patients were less influenced by the prime, this did not lead to a greater reliance on their baseline interpretation. In the Copy condition, the Korsakoff patients were no more likely to provide a final performance identical to their baseline than were the other two groups. In fact, for the Korsakoff patients as well as for the normal controls, a baseline interpretation was given equally frequently whether or not a figure had been copied. Only the alcoholics adhered to their initial percept more frequently in the No Copy than in the Copy task. This latter finding is also seen in the extraneous source of influence, where alcoholics tended to show fewer extraneous responses in the No Copy than in the Copy condition. Apparently, the presence of a priming pattern more directly altered the perceptual interpretation of the ambiguous dot pattern for the alcoholic controls than it did for the other two groups. Although the experience of copying a prime did not directly induce them to draw that pattern, it reduced reliance on their baseline in favor of another response.

When the Zenient scoring (Fig. 3) was applied, the influence of the prime was similar to that seen with the strict criterion. Korsakoff patients still incorporated the prime less frequently in their performance following Copy, even when extraneous lines were allowed in scoring the final drawing. Some evidence of priming was obtained, however, as indicated by the fact that the Korsakoff patients incorporated the prime more frequently in the Copy than in the No Copy condition.

In contrast, group differences in the effects of baseline were no longer reliable using the lenient scoring procedure. This was largely due to the fact that normal controls as well as alcoholics now adhered more closely to their baseline performance in the No Copy than in the Copy condition. This reflects the fact that in the absence of a prime the final performance of the normal subjects was somewhat more variable than that of the alcoholic controls, in that it more frequently included extraneous lines in addition to the baseline.

The influence of baseline responses, however, was not limited to those trials in which the final performance included only the baseline. Sometimes the final drawing incorporated both the baseline and prime, making it impossible to separate their respective contributions. Overall, this joint effect occurred more frequently following Copy than following No Copy, with no group differences. This suggests that on those trials the prime had its effect by combining with the baseline percept. Importantly, this joint influence was equally likely to occur for the Korsakoff patients as for the other groups. This contrasts with the influence of the prime in isolation, which was smaller for the Korsakoff patients than for the other groups, under both the strict and the lenient scoring criteria. This finding


may indicate that the prime has a less specific and less direct effect on the performance of the Korsakoff patients than it does for the normal and alcoholic controls.

On the extraneous measure, use of a lenient scoring resulted in little change compared to the strict scoring. Of course, there were fewer of these responses using lenient scoring, since many were now scored under other sources of influence. The pattern of responses, however, remained the same as before. Extraneous responses occurred more frequently in the NO Copy than in the Copy condition. This was more true for the Korsakoff patients and normal controls than for the alcoholics, but the Group by Task interaction was no longer significant.

These results suggest several broad conclusions. First, amnesic patients show some perceptual priming based on exposure to an experimenter- provided interpretation of an ambiguous array of dots. This parallels the results of a similar study with H.M. (Gabrieli et al., 1990). However, unlike H.M., the Korsakoff patients show less priming than do their nonamnesic controls. In both the Copy and No Copy conditions, Korsakoff patients are more likely to produce final interpretations which are different than either their baseline or an external reference stimulus. This suggests that they may interpret the designs in a less consistent and less specific manner than do the other groups. A stable dot interpretation effect prob- ably depends upon the consistency of basic perceptual processes across repeated presentations. When visual parsing routines are applied incon- sistently, this would limit the effect that previous dot interpretations (both baseline and prime) could have over the course of time. This would explain why factors extraneous to the experimental manipulation seem to con- tribute so much to the Korsakoffs’ final product.

Second, although the Korsakoff patients did not use the copied prime as a direct source of influence for their final interpretation as frequently as did the alcoholics and normal controls, the priming stimulus never- theless did weakly affect their performance. This can be seen under the lenient scoring, where in the Copy condition the Korsakoff patients, like the other groups, used the prime in conjunction with their baseline interpretation to generate a final drawing different from what they had orig- inally produced. This effect was accompanied by a decrease in the effect of extraneous influences. This outcome suggests that the prime might become incorporated into their final percept but may not provide the sole source of influence. Thus, it can be concluded that priming has been demonstrated in Korsakoff patients, although it is less direct and less specific than for the other groups. Rather than obliterating or replacing an initial perceptual interpretation, the prime may have its influence by systematically modifying an existing percept.

Direct and complete reproduction of a priming stimulus may require that the model be explicitly accessed during drawing. The results of Ga-


brieli et al. (1990) are in accord with this proposal, in that they found that cued recall for the primes was at nearly the same level as were the priming scores. In contrast, indirect priming, as observed in the Korsakoff patients, may reflect a change in perceptual fluency that does not depend on explicit access to the model. Unfortunately, a comparison of indirect priming in Korsakoff patients and H.M. cannot be made at this time since the Gabrieli et al. (1990) study did not report lenient scoring results.

A final aspect of the present findings that deserves further comment concerns the performance of the alcoholic controls. For these patients, the direct influence of the prime was virtually the same as for the normal controls. However, the prime had more of a disrupting effect on their baseline interpretation, in that it biased their final performance away from their original performance. On the other hand, in the No Copy condition the alcoholics demonstrated more baseline stability than did the normal controls. These results are in line with other research with alcoholics (Cermak, 1990) in which it has been shown that, left to their own devices, they show less creativity than normals. When distracting material is introduced, however, they are more susceptible to the effects of interfer- ence. Whether this reflects a subtle parsing deficit similar to that hy- pothesized for the Korsakoff patients remains to be determined.

REFERENCES Bentin, S. 1989. Orthography and phonology in lexical decision: Evidence from repetition

effects at different lags. Journal of Experimental Psychology: Learning, Memory and Cognition, 15, 61-72.

Cermak, L. S., Talbot, N., Chandler, K., & Wolbarst, L. R. 1985. The perceptual priming phenomenon in amnesia. Neuropsychologia, 23, 615-622.

Cermak, L. S. 1990. Cognitive processing deficits in chronic alcohol abusers. Alcohol Health and Research World, 14, 130-136.

Gabrieli, J. D. E., Milberg, W. P., Keane, M. M., & Corkin, S. 1990. Intact priming of patterns despite impaired memory. Neuropsychologia, 28, 417-427.

Garner, W. R. 1974. The Processing of information and Structure. Hillsdale, NJ: Erlbaum. Graf, P., & Mandler, G. 1984. Activation makes words more accessible, but not necessarily

more retrievable. Journal of Verbal Learning and Verbal Behavior, 23, 553-568. Jacoby, L. L. 1983. Perceptual enhancement: Persistent effects of repetition: Solving a

problem versus remembering a solution. Journal of Experimental Psychology: Learning, Memory and Cognition, 9, 21-38.

McClelland, J. L., & Rumelhart, D. E. 1981. An interactive activation model of context effects in letter perception. I. An account of basic findings. Psychological Review, 88, 375-407.

Milner, B., Corkin, S., & Teuber, H. L. 1968. Further analysis of the hippocampal amnesia syndrome: 14-year follow-up study of H. M. Neuropsychologia, 6, 215-234.

Roediger, H. L., & Blaxton, T. A. 1987. Retrieval modes produce dissociations in memory for surface information. In D. Gorfein & R. R. Hoffman (Eds.), Memory and cognitive processes: The Ebbinghaus centennial conference. Hillsdale, NJ: Erlbaum.

Warrington, E. K., & Weiskrantz, L. 1968. A new method of testing long-term retention with special reference to amnesic patients. Nature, 217, 972-974.

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Priming of spatial configurations in alcoholic Korsakoff's amnesia