Biomedical subjects

M Verfaellie

Publications and source records attributed to M Verfaellie.

At least 37 records · Page 2Linked to original sources

PubMed1996

Spatial location memory in amnesia: binding item and location information under incidental and intentional encoding conditions.

Items located within an array were presented to alcoholic Korsakoff and nonalcoholic mixed-etiology amnesics and to alcoholic and normal controls. Recognition memory for the locations of items was tested after incidental and intentional encoding. When equated on item recognition, neither Korsakoff amnesics nor alcoholic controls benefited from intentional, relative to incidental, encoding instructions. Furthermore, Korsakoff amnesics showed neither disproportionately impaired incidental nor intentional location recognition memory relative to alcoholic controls. In contrast, mixed-etiology amnesics profited significantly from intentional location acquisition relative to incidental instructions, and were impaired somewhat in incidental, but not intentional, location memory relative to normal controls. We discuss these data in relation to Mayes' (1992) contextual memory deficit hypothesis and Hirst's (1982) automatic encoding deficit account, and propose an alternative framework in which the location memory deficit observed in mixed-etiology amnesics is interpreted as a disruption to the ability to bind item and location information.

Alcohol Amnestic Disorder↗

PubMed1996

Verbal memory function in mild aphasia.

Verbal material may be processed by semantic and phonologic systems. Damage to these language systems may also impair memory. We classified 16 mildly aphasic patients according to phonologic and lexicosemantic abilities, tested them on a variety of short- and long-term memory measures, and correlated behavioral deficits with lesion location. Aphasia impaired both short- and long-term memory. Phonologic impairment affected only digit span performance. Lexicosemantic deficits impaired self-organized encoding of word lists. Memory impairment was not associated with specific lesion locations. Persistent verbal-memory impairments accompanying even mild residual aphasia may be responsible for much of the difficulty mildly aphasic patients experience returning to vocational, academic, and social life. Co-occurrence of these deficits probably reflects their underlying dependence on similar processing systems.

Adult↗

PubMed1995

Knowledge of New English vocabulary in amnesia: an examination of premorbidly acquired semantic memory.

To assess if amnesics have intact remote memory for general semantic information, we examined memory for vocabulary words with known dates of entry into the language between 1955 and 1989. Amnesics of mixed etiology with acute onset performed normally on both a recall and a recognition task. Korsakoff patients, in contrast, were impaired on both tasks and demonstrated a gradient such that their knowledge of words acquired during more recent time periods was worse than that of words acquired during more remote time periods. The improvement in performance associated with recognition testing was larger for Korsakoff patients than for control subjects and correlated significantly with a composite measure of frontal dysfunction. These findings suggest a deficit in the controlled search and retrieval of semantic information in Korsakoff patients. The implications of the differential performance of Korsakoff and mixed etiology amnesics for explanations of temporally graded retrograde amnesia are discussed.

Adult↗

PubMed1995

Comparison of figural intrusion errors in three amnesic subgroups.

To examine the contribution of memory deficits and executive dysfunction to the production of prior-item intrusion errors, Korsakoff, mesial temporal amnesic, and anterior communicating artery aneurysm (ACoA) patients' performance on the Visual Reproduction subtest of the Wechsler Memory Scale-Revised (WMS-R) was assessed. The Korsakoff patients were matched to the mesial temporal group in terms of severity of amnesia, while the ACoA group, which was less severely amnesic, was matched to the Korsakoff group in their performance on executive tests. Results indicated that at immediate recall, Korsakoff patients made significantly more intrusions than mesial temporal and ACoA patients. Conversely, after a delay, ACoA patients tended to make more intrusions than the other groups. Findings suggest that intrusions are due to a combination of deficient memory and executive dysfunction. A further comparison of a subgroup of ACoA patients matched to the Korsakoff patients in terms of severity of amnesia, however, revealed differences in the pattern of intrusions of these two groups, suggesting that different mechanisms may underlie Korsakoff and ACoA patients' susceptibility to interference.

Adult↗

PubMed1995

Amnesia following traumatic bilateral fornix transection.

There is controversy regarding the effect of isolated fornix damage on human memory. We report a patient who suffered a traumatic penetrating head injury that resulted in a significant and persistent anterograde amnesia. CT revealed a lesion that involved the region of the proximal, posterior portion of both fornices without evidence of damage to other hippocampal pathways or to other structures known to be critical for memory, such as the hippocampus, thalamus, or basal forebrain. The unique location of the lesion in this patient provides evidence supporting the role of isolated fornix lesions in amnesia.

Adult↗

PubMed1994

Acquisition of generic memory in amnesia.

Amnesic patients' ability to acquire generic, semantic information was assessed relative to their own level of episodic memory. Patients studied a list of words in which some items were presented twice and others once. Upon each presentation, the words were tagged episodically by presenting them in a unique color. Recall of the colors in which words were presented suggested that individual presentations of repeated items were less likely to be recalled than presentations of nonrepeated items; however, actual recall of repeated items exceeded that of nonrepeated items. This outcome demonstrated that amnesics can recall some items generically without recalling either of their individual presentations. However, amnesics' recall of twice-presented items remained far below that of the control group, even when their recall of once-presented items was matched by testing the control group after a delay. This finding suggests that amnesic patients can acquire new generic knowledge but do so much less efficiently than do normal individuals. Furthermore, this deficit occurs independently of the amnesics' episodic memory impairments, reflecting instead a disruption in semantic learning per se.

Adult↗

PubMed1994

Lateralization of memory for the visual attributes of objects: evidence from the posterior cerebral artery amobarbital test.

We used the posterior cerebral artery amobarbital test to examine how each temporal lobe mediates memory for objects. Temporal lobectomy candidates were presented with four objects while one hemisphere was anesthetized. We assessed recall and recognition following recovery from the drug. Verbal recall was significantly better following object presentation to the left hemisphere when the left hemisphere was not the seizure focus. Recognition memory, tested with two identical objects, two objects that shared the same name but had different physical characteristics, and two foils, was superior following object presentation to the right hemisphere. Only the right hemisphere could discriminate identical objects from same-name foils. These data confirm that the left temporal lobe has an advantage in encoding the verbal representation of an object and suggest that the right temporal lobe is critical for memory of specific visual attributes of objects.

Adult↗

PubMed1993

Episodic effects on picture identification for alcoholic Korsakoff patients.

Experience with degraded pictures produces better subsequent identification of these pictures in amnesic patients. To examine the contribution of episodic memory to this facilitation, we compared identification of pictures that were identical to a studied picture, pictures that shared the same name with a studied picture, and new, unstudied pictures. In an initial phase of the experiment, patients clarified each picture until they could name it. During a second phase, they again clarified each picture and judged whether it was identical, similar (same-name), or different from pictures identified in the first phase. Korsakoff patients, as well as alcoholic controls, identified identical pictures faster than same-name pictures, and these in turn were identified faster than new pictures. The Korsakoff patients did show less facilitation than the alcoholic controls, but this difference was eliminated by testing the alcoholics after a week delay. The smaller facilitation in performance shown by amnesics and by alcoholics tested after a delay was accompanied by impaired recognition memory as well as by qualitative differences in recognition performance. The Korsakoff patients tended to label same-name pictures as different while alcoholic controls tested immediately called them identical, a tendency which disappeared when alcoholics were tested after a delay. These findings suggest that Korsakoff patients are influenced by specific episodic information even more than are alcoholic controls.

Aged↗

PubMed1993

Dissociable cognitive and neural mechanisms of unilateral visual neglect.

We administered two experimental tasks to 16 patients with neglect following unilateral right hemisphere strokes, designed to probe processing of information in the neglected left visual field. A semantic priming/lexical decision task examined implicit processing of stimuli presented to the neglected field, and a discrimination task required explicit recognition of the same stimuli. We grouped patients according to three patterns of performance: (1) poor discrimination in the left visual field but intact priming, (2) normal priming and discrimination in both fields, and (3) normal priming but poor discrimination in both fields. Although patients in group 1 had posterior lesions, patients in groups 2 and 3 had extensive deep anterior lesions. These results suggest that the clinical phenomenon of unilateral visual neglect can be the surface manifestation of deficits in two different and interacting processes--attentional processes (group 1) and intentional processes (group 2)--or it may be a global attentional disturbance superimposed on these deficits (group 3).

Adult↗

PubMed1992

Fluency versus conscious recollection in the word completion performance of amnesic patients.

To examine the relative contribution of fluency and recollection to the word completion performance of amnesics, we administered a task in which patients were told specifically not to utilize previously presented words during stem completion (an Exclusion condition). This condition was contrasted with a standard word completion task in which patients were encouraged simply to complete the stem with the first word that came to mind (an Inclusion condition). Since the exclusion condition necessitated controlled respecification of the initial presentation, it was hypothesized that amnesics would be less able than controls to exclude study list items. Consistent with this hypothesis, the results indicated that the amnesics' performance, unlike that of the alcoholic controls, did not significantly differ as a function of task condition. To examine whether amnesics' conscious recollection could be enhanced, Experiment 2 presented the study list five times. The amnesics now were able to exclude a significant number of items from the study list; however, they still did so considerably less frequently than alcoholic controls. For the alcoholic controls, increasing the number of study trials had little additional effect on their exclusion performance, but it significantly enhanced their inclusion performance. Taken together, these findings suggest that for control subjects, word completion performance is likely mediated by a combination of fluency and recollection, while for amnesic patients, performance is almost exclusively based on the fluency with which an item comes to mind.

Alcohol Amnestic Disorder↗

PubMed1992

Priming of spatial configurations in alcoholic Korsakoff's amnesia.

To examine priming for novel, nonverbal patterns, a modification of the paradigm 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.

Aged↗

PubMed1991

Frontal verbal amnesia. Phonological amnesia.

Although aphasic patients with frontal lobe damage may demonstrate impaired retention of verbal material, significant anterograde memory disturbances have not, to our knowledge, been reported with a minor Broca's aphasia. We describe a patient with minor Broca's aphasia who exhibited an unusual and profound anterograde memory disturbance, especially for phonologically specified stimuli. We suggest that this disturbance is attributable to an impairment in the volitional, controlled search of stored phonological information.

Amnesia↗

PubMed1991

Changing attentional demands in left hemispatial neglect.

Seven variations of a letter cancellation test were used to examine how varying attentional demands affect hemispatial neglect in patients with right hemisphere lesions. While the 14 targets always remained in the same location, the number of distractors (zero, nine, 28, or 82) as well as their complexity (one letter or nine different letters) were varied. The percentage of targets canceled in the left hemispace was linearly related to the number of distractors. There were no differences between the complexity conditions. In a second study, the same 14 targets were presented but the distractors (zero, 14, or 41) were all placed on the right. Increasing the number of distractors on the right increased neglect on both sides of the space. Taken together, these results suggest that, while the limited attentional resources of the left hemisphere are biased toward the right hemispace, the absence of contralateral attentional demands allows these resources to be directed ipsilaterally.

Aged↗

PubMed1991

A further analysis of perceptual identification priming in alcoholic Korsakoff patients.

Alcoholic Korsakoff patients have been shown to have normal repetition priming for words, but impaired priming for pseudowords, on perceptual identification tasks. Because real words, but not pseudowords, have semantic representations, successful priming of real words has been attributed to semantic activation. Alternatively, however, priming might reflect the perceptual, i.e. orthographic and phonological familiarity associated with real words in comparison with pseudowords. In order to examine which of these factors accounts for normal priming by amnesics, Experiment 1 was designed to contrast perceptual identification priming for words, pseudowords and pseudohomonyms (e.g. "phaire"). On this task, Korsakoff patients showed normal priming for real words and for pseudohomonyms, but significantly impaired priming for pseudowords. It was felt that since pseudohomonyms are orthographically unfamiliar but could access semantics through their phonological route, activation of a semantic representation rather than perceptual familiarity might be the critical factor underlying successful priming. Experiment 2 was then designed to further explore the robustness of this semantically mediated priming by presenting different word types within the same study list. Under these conditions, Korsakoffs' pseudohomonym priming was consistently below normal. This suggests that priming in Korsakoff patients depends upon the conceptual salience of the stimuli and not solely on semantic activation.

Alcohol Amnestic Disorder↗

PubMed1991

Repetition effects in a lexical decision task: the role of episodic memory in the performance of alcoholic Korsakoff patients.

To examine the contribution of episodic memory to the successful verbal priming performance of Korsakoff patients, we adapted a lexical decision task which holds constant the processing demands during study and testing. Words and nonwords were repeated at a lag of 0, 1, 3, 8 and 15 items and the decrease in response latency was taken as a measure of priming. In Experiment 1, Korsakoff patients showed repetition priming of a magnitude similar to that obtained by alcoholic controls, even at a lag of 15 intervening items. Experiment 2 explored the effect of word frequency on repetition priming. Korsakoff patients again showed normal priming up to lags of 15, and, as expected, these repetition effects were larger for low frequency than for high frequency words. This outcome was felt to be more consistent with an episodically based familiarity account than with a semantic activation account. Finally, Korsakoff patients were found to be impaired in their ability to use episodic memory in an explicit memory task that used the same material under comparable presentation conditions (Experiment 3). Contemporary processing models of episodic memory are discussed as possible explanations for the successful implicit memory performance by amnesic patients on this task.

Adult↗

PubMed1991

Autonomic and behavioral evidence of "implicit" memory in amnesia.

A profoundly amnesic patient with a left retrosplenial-fornix lesion was tested on a recognition task that evaluated both verbal and electrodermal aspects of new learning. In addition, "implicit memory" tasks (mirror reading and perceptual identification) were given. The patient displayed strong evidence of learning on all tasks although the results of this learning were not represented in explicit recall or recognition. These findings suggest that autonomic as well as behavioral evidence can index spared memory functions in amnesia. The specific meaning of electrodermal recognition and its possible place in the distinction between implicit and explicit memory is discussed.

Adult↗

PubMed1991

Autobiographical memory: influence of right hemisphere damage on emotionality and specificity.

This study investigated the ability of right hemisphere damaged (RHD) patients to recall autobiographical material in response to emotional versus nonemotional cues. A modified Crovitz paradigm was used in which patients were asked to recall a specific episode from their own life that related to a cue word. These episodes were rated for emotionality and specificity by independent raters. Patients also rated the emotionality of their own episodes. Independent raters judged the reports of the RHD patients as less specific and less emotional than those of matched nonneurologic control subjects. This was true for episodes in response to emotional as well as nonemotional cue words. RHD patients' own ratings of these episodes, however, did not differ from those of controls. These findings are discussed in terms of RHD patients' overall difficulties in processing emotional material and in terms of the nature of autobiographical memory.

Aged↗

PubMed1990

Impaired shifting of attention in Balint's syndrome.

We assessed the efficiency of attentional shifts across the horizontal and vertical axes of the visual field in a patient with Balint's syndrome caused by bilateral parieto-occipital infarctions. This was performed using an adaptation of Posner's peripheral cueing paradigm. In contrast to normal controls and patients with unilateral parietal lesions previously reported, this patient did not benefit from cues directing attention to the left or right visual field. She appeared to benefit only when the cues directed attention to the upper visual field. This suggests a defect in shifting attention that may occur following bilateral parietal lesions. We discuss the implications of these findings for the role of the parietal lobes in attentional processes and for our understanding of the behavioral abnormalities observed in Balint's syndrome.

Adult↗