[show abstract][hide abstract] ABSTRACT: We tested the proposal that trace and delay eyeblink conditioning aref fundamentally different kinds of learning. Strings of one, two, three, or four trials with the conditioned stimulus (CS) alone and strings of one, two, three, or four trials with paired presentations of both the CS and the unconditioned stimulus (US) occurred in such a way that the probability of a US was independent of string length. Before each trial, participants predicted the likelihood of the US on the next trial. During both delay (n = 20) and trace (n = 18) conditioning, participants exhibited high expectation of the US following strings of CS-alone trials and low expectation of the US following strings of CS-US trials--a phenomenon known as the gambler's fallacy. During delay conditioning, conditioned responses (CRs) were not influenced by expectancy but by the associative strength of the CS and US. Thus, CR probability was high following a string of CS-US trials and low following a string of CS-alone trials. The results for trace conditioning were opposite. CR probability was high when expectancy of the US was high and low when expectancy of the US was low: The results show that trace and delay eyeblink conditioning are fundamentally different phenomena. We consider how the findings can be understood in terms of the declarative and nondeclarative memory systems that support eyeblink classical conditioning.
[show abstract][hide abstract] ABSTRACT: We examined the importance of awareness for eyeblink conditioning by directly comparing single-cue delay eyeblink conditioning and single-cue trace eyeblink conditioning. During single-cue delay conditioning, participants who became aware of the stimulus contingencies early in the conditioning session conditioned no better than those who became aware later in the session or did not become aware. Thus, the level of awareness was unrelated to the overall level of conditioning across the session. In contrast, awareness of the stimulus contingencies early in the session predicted the success of single-cue trace conditioning. These data, together with earlier findings, show that awareness is irrelevant to single-cue delay eyeblink conditioning but is critical for single-cue trace eyeblink conditioning. The findings from the present study are related to previous findings for differential (CS+ and CS-) eyeblink conditioning and awareness.
[show abstract][hide abstract] ABSTRACT: In humans, the phenomenon of temporally graded retrograde amnesia has been described in the clinic and the laboratory for more than 100 years. In the 1990s, retrograde amnesia began to be studied prospectively in experimental animals. We identified 13 published studies in which animals were given equivalent training at two or more separate times before damage to the fornix or hippocampal formation. Eleven of these studies found temporally graded retrograde amnesia, with the extent of amnesia ranging from several days to a month or two. We consider these studies and also suggest why temporally graded retrograde amnesia has sometimes not been observed. Although the evidence in favor of temporally graded retrograde amnesia is substantial, the inference from this work, that memory is reorganized as time passes, is rather vague and depends on mechanisms yet to be identified. It is therefore encouraging that many opportunities exist for moving beyond purely descriptive studies to studies that involve treatments or manipulations directed toward yielding information about mechanisms.
[show abstract][hide abstract] ABSTRACT: Two patients (E.P. and G.T.) were previously described with damage to amygdala and anterior temporal cortex (S.B. Hamann et al., 1996). Both rated emotions in facial expressions normally (the rating task) when the data analysis followed a method that had revealed an impairment in the well-studied patient S.M. The present study reports findings for a 3rd patient (G.P.) with the rating task and reexamines the data for E.P. and G.T. All 3 patients were also given a labeling task in which they selected, from a list of 6 words, which word they thought best described the emotion expressed by a face. All 3 patients were unmistakably impaired on both tasks. However, the impairment exhibited by these patients is different from S.M.'s impairment. The difference may depend on the etiology (congenital vs. adult-onset lesion) or the site of the damage (relatively selective amygdala damage vs. damage to amygdala as well as anterior temporal cortex).
[show abstract][hide abstract] ABSTRACT: Rats with radio-frequency or ibotenic acid lesions of the hippocampus and rats with radio-frequency lesions of the fornix were tested on the visual paired comparison task (VPC), a test of recognition memory. Memory was assessed at five different delay intervals ranging from 10 sec to 24 hr. All operated groups performed normally at the shorter delays (10 sec and 1 min). Across longer delays, the two groups with hippocampal damage were impaired. Rats with fornix lesions performed well on the VPC task but were impaired on a spatial task (spontaneous alternation). The results show that the hippocampus is essential for normal recognition memory. Moreover, fornix lesions need not mimic the effects of direct damage to hippocampal tissue. The findings are discussed in the context of the contribution of the hippocampus to recognition memory.
Journal of Neuroscience 01/2001; 20(23):8853-60. · 6.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: Amnesic patients and controls listened to verbal descriptions of imaginary animals and then classified novel descriptions according to whether they belonged to the studied category. Controls performed well, but the amnesic patients did not acquire categorical knowledge. These findings contrast with previous demonstrations of intact category learning by amnesic patients for dot patterns, artificial grammars, and cartoon animals. It appears that category knowledge can be acquired implicitly when training exemplars are presented visually and when the similarities among items can be readily perceived. Verbal category learning requires the extraction and retention of meaning from training exemplars that are separated in time and may make demands on declarative memory that are beyond the capacity of amnesic patients.
[show abstract][hide abstract] ABSTRACT: Neuroimaging studies have often failed to observe activity in the hippocampal region during memory retrieval. Recently, two functional magnetic resonance imaging studies reported activity in the hippocampal region associated with recollective success. In both, participants studied pictures of objects and were given a recognition memory test with words that either did or did not name the studied objects. The recognition test was therefore cross-modal or associative in nature. These findings raise the question of what circumstances are required to observe activity in the hippocampal region during memory retrieval. Here, we report that robust hippocampal activity for targets relative to foils occurred during retrieval in a recognition memory task when single words were used at both study and test, as well as when pictures of single nameable objects were used at both study and test. The hippocampal region is involved not just in overtly associative tasks but more broadly in the recollection of recently occurring facts and events.
Journal of Neuroscience 11/2000; 20(20):7776-81. · 6.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: E. P. became profoundly amnesic in 1992 after viral encephalitis, which damaged his medial temporal lobe bilaterally. Because of the rarity of such patients, we have performed a detailed neuroanatomical analysis of E. P.'s lesion using magnetic resonance imaging, and we have assessed his cognitive abilities with a wide range of neuropsychological tests. Finally, we have compared and contrasted the findings for E. P. with the noted amnesic patient H.M, whose surgical lesion is strikingly similar to E. P.'s lesion.
Journal of Neuroscience 10/2000; 20(18):7024-36. · 6.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: The amnesic patient E.P. has demonstrated normal levels of repetition priming and at-chance recognition performance (S. B. Hamann & L. R. Squire, 1997), suggesting that the sense of familiarity used to make a recognition memory judgment is not based on the same mechanism responsible for repetition priming. However, the recognition tests previously used may have discouraged the use of familiarity and encouraged reliance on episodic memory. This issue was addressed in 5 experiments with E.P., 3 other amnesic patients with hippocampal damage, and 8 healthy controls. In Experiments 1-3, which were designed to discourage the use of episodic memory, the amnesic patients were impaired and E.P. performed at chance. In Experiments 4 and 5A, a stem-completion priming task was combined with a recognition memory task on each trial. E.P.'s priming was intact, yet his recognition memory performance was at chance. This suggests that although recognition memory judgments may be made on the basis of familiarity, repetition priming is not the source of this feeling of familiarity.
[show abstract][hide abstract] ABSTRACT: Eighteen monkeys with lesions of the hippocampal region (the hippocampus proper, the dentate gyrus, and the subiculum) made by an ischemic procedure, radio frequency, or ibotenic acid were tested on a simple, two-choice object discrimination learning task that has been shown to be sensitive to large lesions of the medial temporal lobe. The monkeys were also tested on two other discrimination tasks (pattern discrimination and eight-pair concurrent discrimination) that can be learned normally by monkeys with large medial temporal lobe lesions. All of the lesion groups were impaired at learning the simple object discrimination task. Seven of the monkeys who had sustained damage to the hippocampal region also sustained damage to the tail of the caudate nucleus. These seven monkeys, but not the other 11 monkeys with hippocampal lesions, were impaired on pattern discrimination and concurrent discrimination learning. The results suggest that the hippocampal region is important for learning easy, two-choice discriminations, whereas the caudate nucleus is necessary for the normal learning of more difficult, gradually acquired discrimination tasks. The findings support the distinction between declarative memory, which depends on the hippocampus and related medial temporal lobe structures, and habit learning, which depends on the caudate nucleus.
Journal of Neuroscience 06/2000; 20(10):3853-63. · 6.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: Studies of differential eyeblink conditioning (CS+ and CS-) have demonstrated that successful conditioning requires awareness of the stimulus contingencies and that delay conditioning does not. Two experiments were carried out to determine whether awareness is also important for single-cue trace eyeblink conditioning. In experiment 1, participants who performed a secondary, attention-demanding task emitted significantly fewer conditioned eyeblink responses than participants who watched a silent movie during the conditioning session. In experiment 2, participants who became aware of the stimulus contingencies early in the conditioning session emitted significantly more conditioned responses during the remainder of the session than participants who became aware later in the session or who never became aware. These results indicate that awareness is important for single-cue trace eyeblink conditioning, just as it is for differential trace conditioning. The relationship between awareness and trace eyeblink conditioning is discussed in the light of these and other recent findings.
[show abstract][hide abstract] ABSTRACT: The phenomenon of temporally graded retrograde amnesia (loss of information acquired before the onset of amnesia) suggests that the hippocampus, and possibly other medial temporal lobe (MTL) structures, have a time-limited role in memory. In three experiments, we made a first attempt to use fMRI to assess activity in the hippocampal region (the CA fields of the hippocampus, the dentate gyrus, and the subiculum) and the adjacent parahippocampal gyrus (parahippocampal, entorhinal, and perirhinal cortices) during recognition memory testing as a function of study-test interval. Experiment 1 (n = 5) demonstrated activity in the hippocampal region and parahippocampal gyrus for targets relative to foils during recognition memory performance following a single study-test delay of about one-half hour. In Experiment 2, 15 participants studied line drawings at each of three different times prior to scanning: one-half hour, 1 day, and 1 week. fMRI data were then collected during recognition memory testing, using targets from all three delays and foils. While an overall effect of targets vs. foils was found in both the hippocampal region and the parahippocampal gyrus, there was no effect of study-test interval on target activity. In Experiment 3 (n = 13), behavioral performance (reaction time and accuracy) was equated across the three delays. Again, no effect of study-test interval was observed. It is possible that the time span sampled in our study (one-half hour to 1 week) was too short to observe changes in activity. Alternatively, activity in the MTL during memory testing may occur even when these structures are not necessary for retrieval.
[show abstract][hide abstract] ABSTRACT: Monkeys with lesions limited to the hippocampal region (the hippocampus proper, the dentate gyrus, and the subiculum) were impaired on two tasks of recognition memory: delayed nonmatching to sample and the visual paired-comparison task. Recognition memory was impaired in five different groups of monkeys, whether the lesions were made by an ischemic procedure, by radio frequency, or by ibotenic acid. The finding that the hippocampal region is essential for normal recognition memory performance is considered in the context of current ideas about the role of the hippocampus in declarative memory.
Journal of Neuroscience 02/2000; 20(1):451-63. · 6.91 Impact Factor
[show abstract][hide abstract] ABSTRACT: Fifteen or 32 months after the verdict was announced in the O.J. Simpson murder trial, we asked college students about how they had heard the news, and we compared their responses with what they had told us 3 days after the verdict. Our study is the first to have assessed recollective accuracy at two different intervals more than 1 year after a noted public event. The quality of the recollections after 32 months was strikingly different from the quality of the recollections after 15 months. After 15 months, 50% of the recollections were highly accurate, and only 11% contained major errors or distortions. After 32 months, only 29% of the recollections were highly accurate, and more than 40% contained major distortions. Retention interval appears to be an important factor determining the frequency of memory distortions, and differences in the retention interval across studies may account for some of the contradictions in the flashbulb-memory literature. Metamemory errors and source memory difficulties are a likely basis of poor memory performance after long retention intervals. The results highlight the marked qualitative changes in recollections that can occur between 1 and 3 years after information has been acquired.
[show abstract][hide abstract] ABSTRACT: We address the recent suggestion that the "hippocampal system" is important for understanding ambiguities in language (MacKay et al., J Cogn Neurosci 1998;10:377-394). Seven amnesic patients and 11 controls first decided whether a sentence was ambiguous and then tried to explain the ambiguity. Three amnesic patients with damage limited to the hippocampal formation and one amnesic patient with primarily diencephalic damage performed like the controls in all respects. Thus, the ability to comprehend ambiguity is independent of the hippocampal formation. By contrast, three patients with larger temporal lobe lesions, which extended beyond the medial temporal lobe, were impaired to about the same degree as the noted amnesic patient H.M. (as reported by Lackner, Neuropsychologia 1974;12:199-207; MacKay et al., J Cogn Neurosci 1998;10:377-394). Patient H.M., like our 3 impaired patients, has some damage outside the medial temporal lobe. However, patient H.M. also had additional difficulties on these and other language tests that the patients with larger temporal lobe lesions did not exhibit. Accordingly, it is possible that H.M.'s impairment has a different basis.
[show abstract][hide abstract] ABSTRACT: The hippocampus is part of a system of structures in the medial temporal lobe that are essential for memory. One influential view of hippocampal function emphasizes its role in the acquisition and retrieval of spatial knowledge. By this view, the hippocampus constructs and stores spatial maps and is therefore essential for learning and remembering places, including those learned about long ago. We tested a profoundly amnesic patient (E.P.), who has virtually complete bilateral damage to the hippocampus and extensive damage to adjacent structures in the medial temporal lobe. We asked him to recall the spatial layout of the region where he grew up, from which he moved away more than 50 years ago. E.P. performed as well as or better than age-matched control subjects who grew up in the same region and also moved away. In contrast, E.P. has no knowledge of his current neighbourhood, to which he moved after he became amnesic. Our results show that the medial temporal lobe is not the permanent repository of spatial maps, and support the view that the hippocampus and other structures in the medial temporal lobe are essential for the formation of long-term declarative memories, both spatial and non-spatial, but not for the retrieval of very remote memories, either spatial or non-spatial.
[show abstract][hide abstract] ABSTRACT: Exposure to members of a category facilitates later categorization of similar but novel instances of the category. Past studies have suggested that category knowledge can be acquired implicitly and independently of declarative memory. However, these studies have relied on dot pattern stimuli that, unlike most real-world objects, are difficult to verbalize and cannot be broken into component features. It is therefore unclear how relevant such studies are to an understanding of everyday categorization. In the present studies, category learning in amnesic patients was tested with stimuli that both exhibit discrete features and are easy to describe (namely, cartoon animals). Amnesic patients were as competent as healthy volunteers in learning to categorize these animals, despite their impairment in recalling the animals' features. The results suggest that the implicit acquisition of category knowledge is a common process in everyday experience, and that it can occur whenever individuals encounter a large group of related items.
[show abstract][hide abstract] ABSTRACT: Patients with Parkinson's disease (PD) have been shown to be impaired on some nondeclarative memory tasks that require cognitive skill learning (perceptual-motor sequence learning, probabilistic classification). To determine what other skill-based tasks are impaired, 13 patients with PD were tested on artificial grammar learning, artificial grammar learning with transfer to novel lettersets, and prototype learning. Patients with PD performed similarly to controls on all 3 tests. The intact learning exhibited by PD patients on these tests suggests that nondeclarative cognitive skill learning is not a single entity supported by the neostriatum. If learning the regularities among visual stimuli is the principal feature of artificial grammar learning and prototype learning, then these forms of skill learning may be examples of perceptual learning, and they may occur in early visual cortical processing areas.
[show abstract][hide abstract] ABSTRACT: Three amnesic patients with damage limited to the hippocampal formation, a severely amnesic patient with extensive medial temporal lobe damage, and 9 controls were tested on the transverse patterning problem (A + B-, B + C-, and C + A-) and also on 2 control problems. One of the control problems was matched to the transverse patterning problem with respect to the number of pairwise decisions that were required. The 2nd control problem was matched to the transverse patterning problem with respect to the number of trials needed by controls to learn the task. The amnesic patients were impaired at solving both the transverse patterning problem and the control problems. The findings suggest that impaired learning of the transverse patterning problem by amnesic patients derives from their general impairment in declarative memory, which affects performance on most 2-choice discrimination tasks.