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K A Paller

Publications and source records attributed to K A Paller.

26 records · Page 2Linked to original sources
PubMed1991

Indirect measures of memory in a duration-judgement task are normal in amnesic patients.

Nine amnesic patients of mixed aetiology were studied in a duration-judgement task that allowed three measures of memory to be obtained. On each trial of the task, subjects attempted to read a briefly flashed word and to estimate the duration of the flash. Both word identification and duration estimation differed as a function of prior study. Words that were previously studied were identified more often and were estimated to have been flashed for a longer duration than were words not previously studied. These priming effects were found in young subjects in Experiment 1 and in amnesic patients and age-matched control subjects in Experiment 2. Priming effects were normal in the amnesic patients, whereas these patients were severely impaired at recognizing the same words. Previous results have also shown that amnesic patients can perform normally on certain memory tests, including priming of word identification. These results show that priming of duration judgements can also be included in the category of indirect measures of memory that are spared in amnesia.

Adult↗
PubMed1990

Recall and stem-completion priming have different electrophysiological correlates and are modified differentially by directed forgetting.

The notion that different aspects of memory are assessed by explicit and implicit memory tests was supported by behavioral and electrophysiological results. In a study-test procedure, 24 subjects were instructed to remember some words and to forget other words. Free recall and cued recall were better for words associated with the remember instruction, whereas directed forgetting did not influence stem completion (an implicit memory test). Event-related brain potentials elicited during study differed as a function of subsequent memory performance for free recall and cued recall, but not for stem completion. These results implicate encoding differences in the distinction between the 2 types of memory test. Factors governing whether explicit retrieval affects performance on an implicit memory test, mechanisms that may underlie directed-forgetting effects, and the importance of electrophysiological correlates of memory are also discussed.

Adolescent↗
PubMed1988

ERPs predictive of subsequent recall and recognition performance.

By exploiting measures of information processing complementary to those obtained from behavioral studies, electrophysiological studies of human memory may provide insights into the cognitive processes associated with encoding. In the present experiment, subjects viewed words under incidental learning conditions in which each word required a two-choice decision based on semantic criteria (interesting/uninteresting or edible/inedible). Memory for those words was subsequently assessed by a free recall test and then a recognition test. Event-related brain potentials elicited in response to the original presentation of each word were found to differ as a function of later memory performance. Over the 400-800 ms latency range, responses to remembered words were positive relative to responses to forgotten words, especially for recall. These electrophysiological differences are interpreted as reflections of processes that correlated with encoding.

Adult↗
PubMed1988

P3-like brain waves in normal monkeys and in monkeys with medial temporal lesions.

The human brain produces a characteristic electrical response to relevant events that occur unexpectedly. Recent reports have suggested that a prominent part of this event-related brain potential--the P3 wave--may be related to memory functions and may arise from activity within the medial temporal lobe, especially the hippocampus. The latter idea was tested by means of epidural recordings of brain waves in monkeys. Responses to deviant auditory stimuli bore a close resemblance to P3 waves recorded from human subjects under comparable conditions. Monkeys with bilateral lesions of the medial temporal lobe still produced P3-like brain waves, which indicates that medial temporal brain structures are not critical for their generation.

Acoustic Stimulation↗
PubMed1987

Neural correlates of encoding in an incidental learning paradigm.

Event-related brain potentials (ERPs) were recorded during an incidental learning paradigm. Recall and recognition were better for words initially presented in tasks requiring semantic decisions (i.e., 'is it living?' or 'is it edible?') than for words in tasks requiring non-semantic decisions. ERPs elicited during performance of these tasks were predictive of subsequent memory performance. A late positive ERP elicited by words later recalled or recognized was larger than that elicited by words later forgotten. This enhanced positivity for to-be-remembered words could be accounted for, in part, by the fact that words in semantic tasks were remembered better and elicited larger ERPs than did words in non-semantic tasks. Similarly, words followed by affirmative rather than negative decisions were associated both with better recognition and with larger ERPs. However, ERPs were sensitive to processes that influenced later memory performance even within an individual semantic task and within the affirmative decision condition. In addition, results showed that the ERP differences based on later memory performance did not necessarily arise from amplitude variation in P3 waves that occurred at the same time.

Adolescent↗
PubMedDate not supplied

Potentials evoked in human and monkey medial temporal lobe during auditory and visual oddball paradigms.

Event-related potentials (ERPs) were recorded from epileptic patients with electrodes chronically implanted in the medial temporal lobe (MTL) and other intracranial locations, and from monkeys with epidural, transcortical, and MTL electrodes. For both humans and monkeys, the eliciting events consisted of trains of auditory or visual stimuli in which a random 10-20% deviated in pitch or pattern from the remaining stimuli. The distribution of ERPs elicited by the rare (oddball) stimuli in both species was similar, consisting of a P3 recorded from the scalp or cortical surface and a slightly later, but temporally overlapping, focal negativity in the hippocampus and nearby MTL structures. The similarity between the patterns of ERPs in humans and monkeys establishes the feasibility of studying the electrogenesis of P3-like activity with detailed intracranial recordings in an animal model. The data also establish that the MTL ERPs in human patients represent a normal neurophysiological process unrelated to epilepsy.

Acoustic Stimulation↗
PubMedDate not supplied

Consolidating dispersed neocortical memories: the missing link in amnesia.

Consolidation is often conceptualised as a general process by which memory traces can be strengthened in the brain. An alternative idea, developed here, is that a particular sort of consolidation is required for establishing memories belonging to a neurobiologically defined category-memories dispersed across multiple distinct neocortical zones. These memories are consolidated via the formation of a neocortical cell assembly that confers coherence to the set of scattered neocortical memory traces. A set of memory traces linked in this manner can subsequently serve as the basis for conscious recollection. A disruption of this neocortical consolidation process is held to be responsible for the patterns of preserved and impaired memory observed in amnesic patients. A suitable strategy for empirically testing this sort of theory requires an examination of evidence from neuropsychological studies of amnesia and from studies of the neural substrates of memory functions in normal subjects.

Amnesia↗