IMPLICIT MEMORY IN AMNESIC PATIENTS:

Abstract— Previous observations of spared priming in amnesic patients have been based almost entirely on data from visual implicit memory tests Our research examined perceptual priming.in amnesic patients and control subjects on an auditory identification task in which previously spoken words and new words were presented in white noise We manipulated type of encoding task (semantic vs nonsemantic) and speaker's voice at study and test (same vs different) Priming was little affected.by either manipulation, and amnesic patients exhibited normal priming in all experimental conditions On an explicit test of recognition memory, by contrast, amnesic patients exhibited.severely impaired performance following the semantic study task, all subjects showed poor explicit memory following the nonsemantic study task Results are consistent with the idea that auditory priming depends largely on a presemantic auditory perceptual representation system     

Semantic, episodic, and autobiographical memory in a postmeningitic amnesic patient

This study is concerned with the semantic and episodic memory performance of a highly intelligent and intellectually unimpaired patient, K.J., who became amnesic following meningitis. Although densely amnesic he showed unimpaired performance on tests of vocabulary and verbal fluency, while both speed and accuracy on semantic category judgment and sentence verification tests are unimpaired. It is concluded that semantic memory performance may be intact despite dense amnesia. However, this does not necessarily imply separate semantic and episodic memory systems. K.J. showed an impaired capacity for registering new material in semantic memory, and apparently normal autobiographical memory for events occurring well before his illness. The simplest interpretation of our results would therefore appear to be in terms of the sparing of old and overlearned memories rather than the specific preservation of semantic memory.     

Priming of semantic autobiographical knowledge: a case study of retrograde amnesia

The case of a 36-year-old man who suffers dense retrograde and anterograde amnesia as a result of closed-head injury that caused extensive damage to his left frontal-parietal and right parieto-occipital lobes is described. Patient K.C. has normal intelligence and relatively well-preserved perceptual, linguistic, short-term memory, and reasoning abilities. He possesses some fragmentary general knowledge about his autobiographical past, but he does not remember a single personal event or happening from any time of his life. He has some preserved expert knowledge related to the work he did for 3 years before the onset of amnesia, although he has no personal recollections from that period. Some features of K.C.'s retrograde amnesia can be interpreted in terms of the distinction between episodic and semantic memory, and in terms of the distinction between episodic and semantic autobiographical knowledge. K.C.'s semantic knowledge, but not his episodic knowledge, showed progressive improvement, or priming, in the course of the investigation.     

Perceptual priming enhances the creation of new episodic memories

In recent years, most studies of human memory systems have placed the emphasis on differences rather than on similarities. The present study sought to assess the impact of perceptual priming on the creation of new episodic memories. It was composed of three distinct experimental phases: (1) an initial study phase, during which the number of repetitions of target words was manipulated; (2) a perceptual priming test phase, involving both target and new control words, which constituted the incidental encoding phase of (3) a subsequent Remember/Know/Guess recognition task. Results showed that the greater the perceptual priming at encoding, the more the episodic memory performance was enhanced, whereas no such relation was found for know judgments or feeling of familiarity. Furthermore, the words that were associated with the creation of new episodic memories had been perceptually primed to a greater extent during the incidental encoding phase than the words that were subsequently judged to be known or forgotten. These results suggest that the perceptual contents of episodic memories are constituted by the very perceptual representations that generate priming effects. Potential mechanisms linking perceptual priming to the creation of episodic memories are discussed.     

Intact and long-lasting repetition priming in amnesia.

In 2 experiments, we evaluated the ability of amnesic patients to exhibit long-lasting perceptual priming after a single exposure to pictures. Ss named pictures as quickly as possible on a single occasion, and later named the same pictures mixed with new pictures. In Experiment 1, amnesic patients exhibited fully intact priming effects lasting at least 7 days. In Experiment 2, the priming effect for both groups was shown to depend on both highly specific visual information and on less visual, more conceptual information. In contrast, recognition memory was severely impaired in the patients, as assessed by both accuracy and response time. The results provide the first report of a long-lasting priming effect in amnesic patients, based on a single encounter, which occurs as strongly in the patients as in normal Ss. Together with other recent findings, the results suggest that long-lasting priming and recognition memory depend on separate brain systems.     

右侧基底节损伤遗忘症患者的知觉性启动效应与语义性启动效应的分离与定位

采用偏好、自由联想、字根补笔和字辨认等4项任务观察一例单纯性右侧基底节损伤遗忘症患者和两组正常对照的启动效应。结果发现：（1）该患者知觉性启动效应障碍,而语义性启动效应正常。认为知觉性启动效应的神经学基础可能在基底节。（2）该患者知觉性启动效应与语义性启动效应分离。认为神经组织的损伤可导致不同形式启动效应的分离,提出内隐记忆或启动效应的不同形式可能存在不同的神经学基础。     

Neuropsychological dissociations between priming and recognition: a single-system connectionist account

A key claim of current theoretical analyses of the memory impairments associated with amnesia is that certain distinct forms of learning and memory are spared. A compelling example is that amnesic patients and controls are indistinguishable in repetition priming but amnesic patients are impaired at recognizing the study items. The authors show that this pattern of results is predicted by a single-system connectionist model of learning in which amnesia is simulated by a reduced learning rate. They also demonstrate that the model can reproduce the converse pattern in which priming but not recognition is impaired if the input is assumed to be additionally degraded in a priming test. The authors conclude that dissociations between priming and recognition do not require functionally or neurally distinct memory systems.     

Modeling memory and perception

I present a framework for modeling memory, retrieval, perception, and their interactions. Recent versions of the models were inspired by Bayesian induction: We chose models that make optimal decisions conditioned on a memory/perceptual system with inherently noisy storage and retrieval. The resultant models are, fortunately, largely consistent with my models dating back to the 1960s, and are therefore natural successors. My recent articles have presented simplified models in order to focus on particular applications. This article takes a larger perspective and places the individual models in a more global framework. I will discuss (1) the storage of episodic traces, the accumulation of these into knowledge (e.g., lexical/semantic traces in the case of words), and the changes in knowledge caused by learning; (2) the retrieval of information from episodic memory and from general knowledge; (3) decisions concerning storage, retrieval, and responding. Examples of applications include episodic recognition and cued and free recall, perceptual identification (naming, yes–no and forced‐choice), lexical decision, and long‐term and short‐term priming.     

A role for the perceptual representation memory system in category learning

There is growing evidence that working memory, episodic/semantic memory, and procedural memory all play important roles in at least some types of category learning. Little is known, however, about the role of the perceptual representation memory system (PRS). Two experiments are reported that provide evidence that under certain conditions, the PRS, by itself, is sufficient to mediate category learning. Both experiments compared performance in (A, not A) and (A, B) prototype distortion category-learning tasks, in which category exemplars are created by randomly distorting one category prototype in the (A, not A) conditions or two prototypes in the (A, B) conditions. Results showed that (A, not A) performance was more sensitive to prototype similarity and less affected by the removal of feedback than (A, B) performance. These results support the hypothesis that (A, not A) performance was mediated by the PRS, but that (A, B) performance recruited other memory systems.     

Automatic Priming Effects for New Associations in Lexical Decision and Perceptual Identification

Information storage in semantic memory was investigated by looking at automatic priming effects for new associations in two experiments. In the study phase, word pairs were presented in a paired-associate learning task. Lexical decision and perceptual identification were used to examine priming effects during and after the study phase. There was automatic priming for new associations. The priming effect was greatly reduced when different semantic tasks were used at study and test compared to when identical tasks were used at study and test. The results show that new associations in semantic memory can be accessed automatically but are still context dependent. This suggests that rather than being abstract and static, retrieval from semantic memory interacts dynamically with the context.     

Altering access to autobiographical episodes with prior semantic knowledge

Within autobiographical knowledge, semantic and episodic memory are traditionally considered separate, but newer models place them along a continuum, which raises the possibility of an intermediate form of knowledge - personal semantics. This study tested how different types of semantics – general semantics and two forms of personal semantics – impact access to personal episodic memories. In two experiments, participants made a series of true/false judgments about a prime statement, which reflected a general semantic fact, a context-dependent (e.g., repeated event) or context-independent (e.g., trait), personal semantic fact and then retrieved a specific past episodic memory. There was a significantly stronger priming effect for accessing specific episodic memories after judging personal semantic facts versus general facts. We also found that context-dependent and -independent personal semantic facts had separable priming effects on episodic memory. These findings support a continuum model of memory and verifies that there are multiple forms of personal knowledge.     

In what sense is implicit memory "episodic"? The effect of reinstating environmental context

We consider three aspects of the term episodic. Previous literature shows implicit memory does not make conscious autobiographical reference but does code an item's intrinsic context (e.g., perceptual detail). Here, we consider extrinsic context--namely, that not directly processed as part of item identification and not overtly relevant to the task. Study-test mismatch in environmental context (outdoors vs. indoors) reduced memory in an explicit stem-cued recall task but had no effect on repetition priming in an implicit stem completion task. This was true even for very low frequency words. We support the view that implicit memory reflects traces within perceptual (or semantic) knowledge-based systems that are instance specific but do not code the full spatiotemporal context information necessary to support conscious recollection. We also interpret our results as consistent with differences in environmental context specificity between free recall and recognition.     

右侧脑发育不全遗忘症患者的启动效应与右侧皮层的分离

采用ＷＭＳ－ＣＲ、ＷＩＳＣ－ＣＲ和４项内隐记忆任务（偏好、自由联想、字根补笔和字辨认）观察一例右侧大脑发育不全患者和两组正常对照的知觉性启动效应和语义性启动效应。发现该患者智力发育迟滞、记忆功能严重障碍,但两种启动效应正常。显示右侧大脑皮层发育不全不影响两种启动效应任务操作,启动效应与右侧大脑皮层分离。不支持Ｋｅａｎｅ等人认为知觉性启动效应的神经学基础在大脑皮层的结论。结合先的研究结果认为知觉性启动效应可能与基底神经节有关,语义性启动效应可能与左侧大脑皮层有关。     

遗忘症患者外显与内隐记忆实验研究:语义性启动效应任务

采用ＷＭＳ—ＣＲ和ＭＭＳＥ对临床脑损伤患者进行了认知功能与记忆功能两方面的筛选,获得９名遗忘症患者。然后采用偏好和自由联想两项语义性启动效应任务进行测验,发现遗忘症患者在外显记忆受损情况下,的确存在语义性启动效应,且与正常对照相近。推论语义性启动效应任务与遗忘患者损伤的颞叶或间脑结构无关。同时还讨论了启动效应任务,认为偏好任务采用言语性材料不是理想的方法。     

Abstraction and perceptual individuation in primed word identification are modulated by distortion and repetition: a dissociation

One experiment investigated the effects of distortion and multiple prime repetition (super-repetition) on repetition priming using divided-visual-field word identification at test and mixed-case words (e.g., goAT). The experiment measured form-specificity (the effect of matching lettercase at study and test) for two non-conceptual study tasks. For an ideal typeface, super-repetition increased form-independent priming leaving form-specificity constant. The opposite pattern was found for a distorted typeface; super-repetition increased form-specificity, leaving form-independent priming constant. These priming effects did not depend on the study task or test hemifield for either typeface. An additional finding was that only the ideal typeface showed the usual advantage of right hemifield presentation. These results demonstrate that super-repetition produced abstraction for the ideal typeface and perceptual individuation for the distorted typeface; abstraction and perceptual individuation dissociated. We suggest that there is a fundamental duality between perceptual individuation and abstraction consistent with Tulving's (1984) distinction between episodic and semantic memory. This could reflect a duality of system or process.     

On the contribution of perceptual fluency and priming to recognition memory

Repetition priming has been shown to be independent of recognition memory. Thus, the severely amnesic patient E.P. has demonstrated intact stem completion priming and perceptual identification priming, despite at-chance performance on recognition memory tasks. It has also been shown that perceptual fluency can influence feelings of familiarity, in the sense that items perceived more quickly tend to be identified as familiar. If studied items are identified more fluently, due to perceptual priming, and fluency leads to familiarity, why do severely amnesic patients perform no better than chance on recognition memory tasks? One possibility is that severely amnesic patients do not exhibit normal fluency. Another possibility is that fluency is not a sufficiently strong cue for familiarity. In two experiments, 2 severely amnesic patients, 3 moderately amnesic patients, and 8 controls saw words slowly clearing from a mask. The participants identified each word as quickly as possible and then made a recognition (old/new) judgment. All the participants exhibited fluency, in that old responses were associated with shorter identification times than new responses were. In addition, for the severely amnesic patients, priming was intact, and recognition memory performance was at chance. We next calculated how much priming and fluency should elevate the probability of accurate recognition. The tendency to identify studied words rapidly (.6) and the tendency to label these rapidly identified words old (.6) would result in 36% of the studied words being labeled old. Other studied words were identified slowly (.4) but were still labeled old (.4), resulting in an additional 16% of studied words labeled old. Thus, the presence of fluency increases the probability of accurate recognition judgments to only 52% (chance = 50%). This finding explains why amnesic patients can exhibit both priming and fluency yet still perform at chance on recognition tests.     

Long-term follow-up of a childhood amnesic syndrome

In attempting to explain observed dissociations between impaired and preserved memory functioning in amnesia, various dichotomous memory systems (e.g., procedural versus declarative, episodic versus semantic, working versus reference memory) have often been employed. In such cases, the assumption has been that memory subserved by one system is preserved, while that of the other system is impaired. Cohen and Squire have suggested that in amnesia, declarative memory is impaired, although procedural memory is preserved. Long-term follow-up of a densely amnesic patient refutes this view by demonstrating significant anterograde learning of school subjects including reading, vocabulary, spelling, and arithmetic, all of which include some component of declarative memory. It appears that the procedural/declarative dichotomy is not adequate to explain preserved memory in amnesia.     

Psychobiological evidence for the distinction between episodic and semantic memory

The evidence for discrete neurobiological mechanisms that underlie episodic and semantic memory is reviewed. Published data from three separate lines of research are considered: studies of human amnesic patients, psychopharmacological studies of normal human subjects, and studies of working and reference memory in rodents, a distinction that is arguably analogous to the episodic/semantic dichotomy. It is concluded that the available evidence does not indicate that episodic and semantic memory are mediated by discrete neural subsystems. An alternative model of human memory is discussed, based on the concept of parallel distributed processing.An earlier version of this paper was submitted as part of the author's qualifying examination at Emory University.     

Semantic memory disorders

Semantic memory encompasses knowledge of objects, facts and words. A number of brain regions are probably involved, but the left infero-lateral temporal lobe appears to play a key role. The separability of semantic memory from episodic (or autobiographical) memory is a focus of current debate. Impaired semantic memory is a common feature of Alzheimer's disease but is invariably overshadowed by a profound deficit in episodic memory. In semantic dementia, a rarer disorder associated with focal temporal-lobe atrophy, there is selective loss of semantic memory, characterized by preservation of superordinate knowledge of words, and objects, but loss of finer-grained information. This pattern can be interpreted as a degradation of features from a distributed network of semantic representations. Following Herpes simplex encephalitis, patients sometimes show disproportionate loss of knowledge for natural kinds (e.g. animals) with relative preservation of knowledge about artefacts, this may reflect differential damage to neural systems critical for perceptual as opposed to functional features, perceptual properties being more salient in knowledge about natural kinds.     

Posthypnotic amnesia for recently learned material: Interactions with “episodic” and “semantic” memory

In two experiments, posthypnotic amnesia was suggested for a word list memorized during hypnosis. After an initial test of amnesia the subjects gave word associations (Experiment 1) or category instances (Experiment 2) to stimuli intended to elicit the critical (word list) items covered by the amnesia. The extent of initial amnesia observed was strongly associated with measured hypnotic susceptibility. Even among the most hypnotizable subjects, however, the dense amnesia did not prevent the critical items from being elicited by the semantic memory tasks, nor did it modulate the priming which these associations received by virtue of the prior learning experience. Moreover, production of the critical items did not, in general, remind the amnesic subjects of those items which they had previously learned, but could not now remember. Full memory was restored after the amnesia suggestion was canceled by a prearranged cue. Posthypnotic amnesia appears to represent a temporary dissociation of episodic features from memory traces, so that the subject has difficulty in reconstructing the context in which the target events occurred.