Biomedical subjects

M Verfaellie

Publications and source records attributed to M Verfaellie.

48 records · Page 3Linked to original sources

PubMed1990

Strategic and automatic priming of semantic memory in alcoholic Korsakoff patients.

To examine whether the organization of semantic memory is intact in alcoholic Korsakoff patients, three semantic memory tasks which do not require active search for stored information were administered to a group of Korsakoff patients and alcoholic controls. The first two tasks used a perceptual identification paradigm in which patients had to identify briefly presented targets preceded by associatively (experiment 1) or categorically (experiment 2) related primes. On both tasks, Korsakoff patients demonstrated intact priming effects. Because priming in these tasks was thought to reflect the operation of strategic processes, experiment 3 was designed to assess automatic spreading activation using a lexical decision task. Here as well, Korsakoff patients demonstrated intact priming. Taken together, these results support the view that the organization of semantic memory in Korsakoff patients has not been disrupted by their brain injury. The implications of these findings for understanding Korsakoff patients' impaired performance on semantic search tasks are discussed.

Aged↗

PubMed1990

Hemispheric asymmetries in attentional control: implications for hand preference in sensorimotor tasks.

Liepmann (1908) proposed that handedness reflects the greater capacity of one hemisphere to learn the execution of skilled movements. Although asymmetries in motor control are an important basis for hand asymmetries, recent studies have suggested that handedness may be determined by multiple factors. In the present study, we examine how attentional asymmetries may contribute to hand preferences. Right-handed subjects participated in a reaction time task in which they were given preliminary information about where a target stimulus would occur (selective attention) or which hand to use for responding (selective intention). Our findings indicate that these processes influence each other reciprocally and favor a state of optimal attentional and intentional preparation of the right hand. We suggest that these hemispheric asymmetries in attentional control contribute to hand preferences in certain sensorimotor tasks.

Adult↗

PubMed1990

Three-dimensional computergraphic analysis of apraxia. Neural representations of learned movement.

The left cerebral hemisphere in man contains anatomical structures specialized not only for language but also for higher-order motor programming. One method of studying the nature of these motor programs is by observing the type of errors made by patients who have left hemisphere damage. A major problem, however, in investigating the disorders that result from failure of this specialized left hemisphere system (the apraxias) has been the difficulty in obtaining objective measurement of movement in three-dimensional space. To this end, we provide the first three-dimensional analysis of the nature of movement errors in apraxia. Two apraxic subjects with lesions to the left hemisphere and 5 matched control subjects were studied. The apraxic subjects showed impairments in the control of movement timing and spatial relations, as well as decoupling in the normally tight relation between certain spatial and temporal aspects of their movement trajectories. Further, the use of the distal musculature by apraxic subjects was more impaired than their use of the proximal musculature, suggesting more distal representation in any space-time maps of learned movement. These data provide further insight into the nature of the representations of learned skilled movements in the left cerebral hemisphere.

Aged↗

PubMed1990

Effects of changes in stimulus contingency on visual extinction.

Left visual field (LVF) extinction during double simultaneous stimulation (DSS) is common in patients with right cerebral lesions. A postulate is that during DSS, the intact left hemisphere's limited attentional capacity is directed to right hemispace, resulting in LVF extinction. External cueing may help direct attention to the LVF and improve performance. In the present study, we varied patterns of unilateral stimulation preceding DSS in an attempt to redirect attention through expectancy. Nine patients (7 stroke, 2 tumor) with right hemisphere lesions each had 40 DSS trials with the distribution of unilateral stimulation trials systematically varied. Mean extinction percentages on DSS trials were 17% following 5 right unilateral trials, 30% following 1 right unilateral trial, 52% following 1 left unilateral trial, and 63% following 5 left unilateral trials. These findings indicate that the probability of extinction decreases following unilateral stimulation to the right visual field and increases following unilateral stimulation to the LVF. These results suggest that expectancy alters the attentional bias which mediates extinction.

Adult↗

PubMed1989

Selective attention in hemispatial neglect.

To determine how increasing demands on visual selective attention affect the symptoms of hemispatial neglect, we studied patients with right hemispheric lesions on a cancellation task requiring various degrees of focused attention. In the target only condition, the patients were to cancel all stimuli. In the target-nontarget condition, discriminating targets from nontargets did not require close scrutiny, whereas in the target-foil condition, discriminating targets from foils required greater attention to detail. Our findings indicate that increasing demands on visual selective attention adversely affect both exploration of the left side of space and visual discrimination.

Analysis of Variance↗

PubMed1989

Verbal and nonverbal right hemisphere processing by chronic alcoholics.

The theory that chronic alcoholism produces a right hemisphere deficit has generally been tested using visuospatial tasks. The present report tested the theory using three tasks that tap functions, other than visuospatial abilities, which have been failed by patients with right hemisphere damage. The first task assesses the ability to draw a correct inference by integrating information from two unrelated sentences. The second taps the patient's capacity to appreciate humor. The third requires the patient to interpret the emotion displayed in a face. On all three tasks, the pattern of responses of chronic alcoholics differed from that of patients with right hemisphere damage. Thus, the right hemisphere deficit theory fails to gain support from this investigation. On the other hand, the chronic alcoholics' performance was impaired relative to contemporary controls on the first two tasks, although not on the last. On the first two tasks, alcoholics' impairment approximated, and in one instance exceeded, that seen in normal elderly controls. Thus, a premature aging hypothesis received modest support from this study.

Aged↗

PubMed1988

Attentional factors in the occurrence of stimulus-response compatibility effects.

Two major hypotheses have been advanced to account for stimulus-response compatibility effects in the situation in which the location of the target is irrelevant for choosing the correct response. According to the attentional hypothesis, compatibility effects reflect a response bias, favoring the effector on the same side as the stimulus. According to the coding hypothesis, compatibility effects result from a correspondence between the spatial codes of the stimulus and effector. In the present study, two components of attention--selective attention and intention--were independently manipulated by providing selective preparatory information before onset of a target stimulus. Attentional information indicated where the target stimulus would occur; intentional information indicated which hand would have to be used to respond. Compatibility effects were observed only in the condition in which intentional information, but no attentional information, was provided. These findings support the attentional hypothesis and indicate that a specific aspect of attention, namely a selective readiness to respond to the stimulus, is a necessary condition for compatibility effects to occur.

Adolescent↗

PubMed1988

Hemispheric asymmetries in mediating intention, but not selective attention.

Heilman and Van Den Abell [Neuropsychologia 17, 315-321, 1979] reported a right hemisphere dominance for cerebral activation. In the present study, we further examined the nature of this finding in an experimental paradigm in which selective attention and intention (response readiness) were manipulated independently. Normal subjects were tested on a choice reaction time task in which they were given preliminary information about where a target stimulus would occur (selective attention) and which hand to use for responding (intention). Our findings indicate that at short foreperiod durations, the right hemisphere is superior for mediating intention. There was no evidence for a right hemisphere superiority for selective attention.

Adult↗

PubMed1988

Impaired acquisition of temporal information in retrosplenial amnesia.

In this paper we describe the performance of an amnesic with a left retrosplenial lesion on three memory tasks assessing his ability to judge when a previously learned event had occurred. This patient was dramatically impaired in acquiring temporal information about new stimuli, and this defect could not be attributed to recognition failures or to frontal lobe dysfunction. In contrast to his impaired acquisition of temporal information, he had no difficulty judging the temporal order of remote historical events. The pattern of performance displayed by this patient suggests a specific defect in "time-tagging" of new incoming information.

Adult↗

PubMed1988

Electrodermal discrimination of familiar but not unfamiliar faces in prosopagnosia.

It has been previously shown that prosopagnosics can electrodermally "recognize" faces they cannot verbally identify and with which they feel no familiarity. This study extended previous results by showing that electrodermal discrimination of faces exists only on a famous face identification task, and not on a matching-to-sample task involving unfamiliar faces. This suggests that electrodermal recognition reflects the activation of stored identity-specific information built up on the basis of past contact with faces, and provides a psychophysiological distinction between familiar and unfamiliar face processing. Implications for cognitive models of face recognition, and for understanding the nature of prosopagnosia, are discussed.

Agnosia↗

PubMed1987

Response preparation and response inhibition after lesions of the medial frontal lobe.

Two patients with chronic unilateral medial frontal lobe lesions, including the supplementary motor area, were given tasks of response preparation and response inhibition. Whereas the patient with a left-sided lesion, like normal controls, did benefit from preparatory information regarding a subsequent response, the patient with a right-sided lesion did not. On a task requiring the inhibition of an inappropriate response, the patient with a left-sided lesion again performed normally. Conversely, the patient with a right-sided lesion had significant problems inhibiting the extremity contralateral to the lesion. We postulate that the medial frontal lobe may participate in response preparation and response inhibition by modulating the levels of excitability of the motor systems. Our findings also suggest that the right hemisphere may have a dominant role in mediating these processes.

Aged↗

PubMed1987

Retrosplenial amnesia.

A 39-year-old man developed retrograde and anterograde amnesia following haemorrhage from an arteriovenous malformation situated near the splenium of the corpus callosum. MRI studies demonstrated damage to the splenium, and to a region containing the retrosplenial cortex and the cingulate bundle. The fornix was anterior and inferior to the site of maximal damage, but may have been involved; the stria terminalis was probably spared. Structures known to be important in memory but spared by the lesion included the hippocampus, thalamus, and basal forebrain. The retrosplenial cortex receives input from the subiculum and projects to the anterior thalamus, thus providing an alternative route between hippocampus and thalamus. Perhaps more importantly, medial temporal structures involved in memory receive anterior thalamic input directly via the cingulate bundle and indirectly through a relay in the retrosplenial cortex. We suggest that this thalamocortical portion of Papez' circuit may be important in memory, and that lesions of the cingulum and retrosplenial cortex may cause amnesia by disrupting this pathway.

Adult↗