Biomedical subjects

J Blanc-Garin

Publications and source records attributed to J Blanc-Garin.

13 recordsLinked to original sources

PubMed1994

Right hemisphere semantic performance and competence in a case of partial interhemispheric disconnection.

Various forms of right hemisphere (RH)-spontaneous or provoked--performance changes were observed in a partial split-brain patient. Variations in hemispheric activation levels and their interhemispheric balance were retained as the most plausible mechanisms for accounting for these facts. This article presents our attempts to obtain higher RH lexical semantic performance than that observed in a preliminary study where RH performance was at chance level: two forms of the dual-task paradigm were used in order to improve the expression of an assumed RH potential for lexical semantics. Experiment 1 was aimed at activating the RH with a visuo-spatial task as a prior activity before each semantic decision trial. Experiment 2 was intended to overload LH processing systems with a concurrent verbal memory task and induce RH release from LH inhibition. As expected, better RH lexical semantic performance was obtained in these two conditions. Using pictures as stimuli, the aim of Experiment 3 was to observe the spontaneous temporal course of RH implementation in a semantic decision task devoid of written words. These results are discussed along with the issues of performance/competence and the dynamics of neurocognitive function.

Aphasia↗

PubMed1993

Right hemisphere performance and competence in processing mental images, in a case of partial interhemispheric disconnection.

The objective of this study was to analyze dynamic aspects of right hemisphere implementation in processing visual images. Two tachistoscopic, divided visual field experiments were carried out on a partial split-brain patient with no damage to the right hemisphere. In the first experiment, image generation performance for letters presented in the right visual field (/left hemisphere) was undeniably optimal. In the left visual field (/right hemisphere), performance was no better than chance level at first, but then improved dramatically across stimulation blocks, in each of five successive sessions. This was interpreted as revealing the progressive spontaneous activation of the right hemisphere's competence not shown initially. The aim of the second experiment was to determine some conditions under which this pattern was obtained. The experimental design contrasted stimuli (words and pictures) and representational activity (phonologic and visuo-imaged processing). The right visual field (/left hemisphere: LH) elicited higher performance than the left visual field (/right hemisphere, RH) in the three situations where verbal activity was required. No superiority could be found when visual images were to be generated from pictures: parallel and weak improvement of both hemispheres was observed across sessions. Two other patterns were obtained: improvement in RH performance (although LH performance remained superior) and an unexpectedly large decrease in RH performance. These data are discussed in terms of RH cognitive competence and hemisphere implementation.

Attention↗

PubMed1989

Spatial performance and perceptual asymmetries in beginning readers: shift of hand advantage in dichhaptic tasks.

The stability of perceptual asymmetries was studied in two groups of 6-year-old, right-handed children (normal, NL, and poor, PL) learning reading, by means of two experiments occurring at a year's interval (Experiment I and Experiment II). A dichhaptic procedure derived from S. F. Witelson's method (1974, Cortex, 10, 3-17) was used. With group data, perceptual asymmetries were stable over time, whereas with individual data, perceptual asymmetries were highly variable. NL children demonstrated a left-hand advantage at the group level in both Experiment I and Experiment II, with relatively little individual evolution over time. No significant hand advantage was found in PL children in Experiment I, but dramatic alterations occurred in Experiment II where all PL children shifted to a left-hand advantage. This shift was accompanied by an improvement in spatial performance. Such changes in perceptual asymmetry might be of an adaptive nature. Individual changes across time may be related to developmental plasticity (cerebral maturation) and/or neurocognitive flexibility (differential activation of cerebral subsystems).

Attention↗

PubMed1987

Tactual laterality effects and the processing of spatial characteristics: dichaptic exploration of forms by first and second grade children.

Tactual laterality effects (T.L.E.) were examined in first- and second-grade children when performing a dichaptic task. Our procedure, a modified version of Witelson's standard dichaptic task, emphasized the type of errors made, so that we could construct a weighted index (W.I.) for scoring rather than a strictly dichotomous one. The same data were compared using the two types of scoring indexes stated above. T.L.E. occurred consistently with the W.I. scores only, both in two independent groups or in the same group at a year's interval, suggesting (1) that a strictly dichotomous index might lead to loss of information, (2) that the results are reliable at least at the group level. Results are discussed in terms of possible applications of such a procedure to investigating the relationship between performance (spatial processing) and brain organization (hemispheric balance).

Child↗

PubMed1983

Elaboration of representations in a left-handed subject with callosal damage.

Four experiments were carried out in a familial left-handed patient who, following a vascular accident, underwent a callosal lesion and had a right hemianopia. Previous observations by Poncet et al. (1978) demonstrated that both hemispheres controlled expressive language. In the first experiment haptic unimanual exploration showed that each system (right hand/left hemisphere; left hand/right hemisphere) elaborated very different mental representations of the stimulus and gave different types of verbal report of it (naming and talking about). In the second experiment, manual exploration of a maze in the search of a target was performed randomly with the right hand and following a competent spatial strategy with the left hand. The third experiment investigated the ability of the right hemisphere to discriminate the phonetic features of the names of objects that were identified but not named. In the fourth experiment, recognition memory of objects was shown to be better when information was processed by the left hand - right hemisphere system than by the right hand - left hemisphere system. Findings are discussed in terms of verbal vs. non-verbal processes and of perceptual awareness.

Adolescent↗

PubMed1980

Visual evoked potentials and sensory dimensions.

Concomitant variations of physical stimulus characteristics and variations of responses elicited in the human adult subject were studied under conditions of adaptation to darkness or light in order to stimulate the B or the D sub-system described by Jung. Temporal processing in these two systems was compared by analysing output variables (VEPs and sensory ratings) in response to a range of electrophysiological and perceptual responses run in parallel: the temporal summation law, which is a basic code in the nervous system, is found to be obeyed in both B and D subsystems. But asymmetries are also observed, indicating specific characteristics of B and D functioning.

Adult↗

PubMed1976