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Biomedical subjects

D L Schacter

Publications and source records attributed to D L Schacter.

11 recordsLinked to original sources
PubMed1992

Implicit knowledge: new perspectives on unconscious processes.

Recent evidence from cognitive science and neuroscience indicates that brain-damaged patients and normal subjects can exhibit nonconscious or implicit knowledge of stimuli that they fail to recollect consciously or perceive explicitly. Dissociations between implicit and explicit knowledge, which have been observed across a variety of domains, tasks, and materials, raise fundamental questions about the nature of perception, memory, and consciousness. This article provides a selective review of relevant evidence and considers such phenomena as priming and implicit memory in amnesic patients and normal subjects, perception without awareness and "blindsight" in patients with damage to visual cortex, and nonconscious recognition of familiar faces in patients with facial-recognition deficits (prosopagnosia). A variety of theoretical approaches to implicit/explicit dissociations are considered. One view is that all of the various dissociations can be attributed to disruption or disconnection of a common mechanism underlying conscious experience; an alternative possibility is that each dissociation requires a separate explanation in terms of domain-specific processes and systems. More generally, it is concluded that rather than reflecting the operation of affectively charged unconscious processes of the kind invoked by psychodynamic or Freudian theorists, dissociations between implicit and explicit knowledge are a natural consequence of the ordinary computations of the brain.

Amnesia↗
PubMed1992

Understanding implicit memory. A cognitive neuroscience approach.

Dissociations between implicit and explicit memory have attracted considerable attention in recent memory research. A central issue concerns whether such dissociations require the postulation of separate memory systems or are best understood in terms of different processes operating within a single system. This article presents a cognitive neuroscience approach to implicit memory in general and the systems-processes debate in particular, which draws on evidence from research with brain-damaged patients, neuroimaging techniques, and nonhuman primates. The article illustrates how a cognitive neuroscience orientation can help to supply a basis for postulating memory systems, can provide useful constraints for processing views, and can encourage the use of research strategies that the author refers to as cross-domain hypothesis testing and cross-domain hypothesis generation, respectively. The cognitive neuroscience orientation suggests a complementary role for multiple systems and processing approaches.

Animals↗
PubMed1992

Priming and recognition of transformed three-dimensional objects: effects of size and reflection.

In 2 experiments exploring memory for unfamiliar 3-dimensional objects, Ss studied drawings under conditions that encouraged encoding of global object structure. Implicit memory for objects was assessed by a judgment of structural possibility; explicit memory was assessed by recognition. The principal manipulation was the relationship between the sizes or the left-right parities of the studied and tested objects. Priming was observed on the possible-impossible object decision task despite transformations of size or reflection. Recognition, by contrast, was significantly impaired by the transformations. These results suggest that a structural description system constructs representations of objects invariant over size and reflection, whereas a separable episodic system encodes these transformations as properties of an object's distinctive representation in memory.

Adult↗
PubMed1992

Auditory priming: implicit and explicit memory for words and voices.

Five experiments explore priming effects on auditory identification and completion tasks as a function of semantic and nonsemantic encoding tasks and whether speaker's voice is same or different at study and test. Auditory priming was either unaffected by the study task manipulation (Experiments 2, 4, and 5) or was less affected than was explicit memory (Experiments 1 and 3). Study-to-test changes of speaker's voice had nonsignificant effects on priming when white noise masked target items on the identification test (Experiments 1 and 2) or the stem-completion test (Experiment 5). However, significant voice change effects were observed on priming of completion performance when stems were spoken clearly (Experiments 3 and 4). Results are consistent with the idea that a presemantic auditory perceptual representation system plays an important role in the observed priming. Alternative explanations of the presence or absence of voice change effects under different task conditions are considered.

Adult↗
PubMed1992

Implicit and explicit memory for novel visual objects in older and younger adults.

Two experiments examined effects of aging on implicit and explicit memory for novel visual objects. Implicit memory was assessed with an object decision task in which subjects indicated whether briefly exposed drawings represented structurally possible or impossible objects. Explicit memory was assessed with a yes-no recognition task. On the object decision task, old and young subjects both showed priming for previously studied possible objects and no priming for impossible objects; the magnitude of the priming effect did not differ as a function of age. By contrast, the elderly were impaired on the recognition task. Results suggest that the ability to form and retain structural descriptions of novel objects may be spared in older adults.

Adolescent↗
PubMed1992

Absence of explicit or implicit memory in patients anesthetized with sufentanil/nitrous oxide.

Verbal paired associates were presented to 25 surgical patients from initial incision to closure of the incision during general anesthesia. Sufentanil with nitrous oxide and oxygen was administered; intravenous morphine (0.05 mg/kg) was administered when the skin suturing was completed; no volatile anesthetic agents or benzodiazepines were administered. When ready for discharge from the postanesthesia care unit, and again 2 weeks later by telephone, patients were tested for free recall, cued recall, recognition, and free association. No evidence of explicit memory for the word list was demonstrated by patients on tests of free recall, cued recall, or recognition, nor did a free-association test of implicit memory demonstrate a significant priming effect, in contrast to previous results obtained with isoflurane. The precise conditions under which surgical events can be processed, and retained in the form of implicit memory outside of conscious awareness, remain to be determined.

Adult↗
PubMed1991

Implicit memory for possible and impossible objects: constraints on the construction of structural descriptions.

Four experiments examined implicit memory or priming effects on an object decision task in which subjects decided whether structurally possible or impossible novel objects could exist in three-dimensional form. Results revealed equivalent levels of priming for possible objects after 1 vs. 4 5-s exposures to the same structural encoding task (Experiment 1) and when objects were studied with a single structural encoding task or 2 different structural encoding tasks (Experiment 3). Explicit memory, by contrast, was greatly affected by both manipulations. However, priming of possible objects was not observed when Ss were given only a single 1-s exposure to perform a structural encoding task (Experiment 2). No evidence for priming of impossible objects was observed in any of the 4 experiments. The data suggest that object decision priming depends on a presemantic structural description system that is distinct from episodic memory.

Attention↗
PubMed1991

The relation between source memory and aging.

Previous research has shown that elderly adults have difficulty recalling the source of recently acquired facts but does not indicate whether source memory is more impaired than fact memory. This study examined old and young subjects' memory for novel facts that had been read to them by 1 of 2 experimental sources either in a random order or in a blocked order. When fact memory was equated in young and old at different levels of performance, the elderly exhibited disproportionate source memory deficits in the blocked condition but not in the random condition. Results suggest that the relation between fact and source memory in the elderly varies across experimental conditions.

Adult↗
PubMed1977

EEG theta waves and psychological phenomena: a review and analysis.

In this paper, studies which have explored the relation between EEG theta waves and psychological phenomena in normal human subjects are reviewed. It is noted that increases in theta activity occur in conjunction with several kinds of psychological processes. The importance of ocnsidering properties of theta activity, such as amplitude, rhythmicity and scalp topography when analyzing the relation between theta and psychological processes is emphasized. Although there is some evidence for a relationship between theta and psychological processes, it is concluded that the degree to which properties of theta activity are systematically related to specific psychological processes is not yet known.

Affect↗