Biomedical subjects

S Chokron

Publications and source records attributed to S Chokron.

30 records · Page 2Linked to original sources

PubMed1997

Length representation in normal and neglect subjects with opposite reading habits studied through a line extension task.

In the first part of this paper, 45 French (left-to-right readers) and 30 Israeli (right-to-left readers) normal dextrals were given half a line and requested to construct the missing other with the same length (either the left one or the right one). Using this line extension task, a significant effect of reading habits on the performance was found, with no significant bias for Israeli subjects, and a significant underconstruction when building the left half from the right one for French subjects. In the second part, two patients with opposite reading habits (one French, one Israeli) suffering from left unilateral neglect were submitted to the same protocol. Both patients were found to under-construct the right half of the line from the left given half, and to over-construct the left half from the right given one, hence reproducing the well-known line bisection bias. Results are discussed with regard to enhancement and activation hypotheses, and current theories of the neglect syndrome.

Adult↗

PubMed1997

Patterns of dissociation between left hemineglect and deviation of the egocentric reference.

Sixteen control subjects and six right brain-damaged patients with left hemiparesis (three showing signs of left unilateral neglect, three with no signs of neglect) performed a straight-ahead pointing task with their right hand while blindfolded. The aim was to test the hypothesis that the egocentric reference shows significant ipsilesional deviation in left neglect patients. We found no correlation between the position of the egocentric reference and the presence of neglect signs. Neglect patients, like non-neglect patients, showed leftward, rightward or no significant deviation when pointing straight ahead. Results are discussed with reference to egocentric hypotheses of neglect and experimental remission of neglect.

Adult↗

PubMed1995

Variations of the egocentric reference among normal subjects and a patient with unilateral neglect.

Thirty normal subjects and a patient with a left unilateral neglect were submitted to a straight-ahead pointing task in the three following trunk orientations: head and trunk aligned at 0 degree, and trunk rotated 15 degrees to the left or to the right relative to the head. The position of the egocentric reference was found to be dependent upon the trunk orientation, lateralization of the motor response and starting position, and thus on motor direction. The results are discussed with regard to egocentric hypotheses of neglect, spatio-motor cueing and scanning direction.

Adult↗

PubMed1995

Reading habits and line bisection: a developmental approach.

120 normal right-handed subjects, children and adults, with opposite reading habits (60 French, left-to-right readers, 60 Israeli, right-to-left readers) and 60 pre-school children (30 French and 30 Israeli), were submitted to a visuo-motor bisection task. Bisection is found to be dependent upon reading habits with a leftward deviation of the subjective middle for left-to-right readers, and a rightward bias for right-to-left readers. Even before formal reading learning, French and Israeli pre-school children differ significantly in bisecting a line. Results are discussed with respect to hemispheric activation theories and directional hypotheses.

Adolescent↗

PubMed1995

[Influence of post-infarction myocardial revascularization on the prevalence of delayed potentials].

It has been shown that the presence of ventricular late potentials is a predictive factor of ventricular tachycardia and sudden death after myocardial infarction. The value of thrombolysis in the reduction of the prevalence of ventricular late potentials is now well established. However, the effects of other modes of revascularisation is less well known and more controversial. The authors undertook a retrospective study of 139 consecutive patients undergoing coronary angiography after primary myocardial infarction. The presence of ventricular late potentials fulfilling two of the three usual criteria was sought after a revascularisation procedure. The overall prevalence of ventricular late potentials was 30.9%. This was not affected either by the site of infarction of by the single or multiple character of the coronary artery disease. In addition, the left ventricular ejection fraction was not significantly different in patients with positive ventricular late potentials compared with the others. On the other hand, revascularisation of the culprit lesion responsible for the infarction was strongly correlated with a lower incidence of ventricular late potentials (p < 10 (-5)). In particular, the different incidence of positive late potentials between the dilated (9.3%) and non-dilated group (49.2%) was statistically significant (p < 10 (-6)) without any correlation to the single or multiple character of the coronary disease. The authors discuss the different reports in the literature concerning the effects of angioplasty and coronary bypass surgery on the incidence of ventricular late potentials. Conclusion; the review of the literature shows that thrombolysis significantly reduces the incidence of late potentials after myocardial infarction and the present study suggests that angioplasty and coronary bypass surgery may also be effective.

Arrhythmias, Cardiac↗

PubMed1993

Egocentric reference and asymmetric perception of space.

Normal dextrals performed tactilo-kinesthetic bisection tasks in a median position, at three directions of gaze: 30 degrees to the left, 30 degrees to the right, 0 degree. Instead of pseudoneglect phenomenon, a deviation of the subjective middle to the side opposite to the direction of gaze and hand use was found, whichever hand was used. The results are interpreted in terms of displacement of the position of the egocentric reference and are discussed with respect to activation theory. It is argued that pseudoneglect is part of a more general asymmetric perception of space phenomenon which depends on the position of the egocentric reference.

Adult↗

PubMed1993

Influence of reading habits on line bisection.

The effect of scanning direction on perception of space is studied with a visuo-motor bisection task, among 120 normal dextrals with opposite reading habits (60 French subjects, 60 Israeli subjects). Bisection is found to depend upon subject's reading habits. Israeli bisected the line to the right of the objective centre, while French subjects placed their subjective middle to the left of the objective one. Results are discussed with respect to hemispheric activation theories, directional hypotheses and the neglect syndrome.

Adolescent↗

PubMed1992

Pseudoneglect and reversed pseudoneglect among left-handers and right-handers.

Two experiments were carried out to examine specific hand contribution to pseudoneglect and reversed pseudoneglect phenomena in dextrals and sinistrals when bisection tasks were conducted exclusively in the midline spatial condition. Both dextrals and sinistrals showed the same overall pattern deviation: in the tactile scanning task, both right and left hands deviated to the left of the midpoint and in the kinesthetic scanning tasks, the right hand deviated to the left and the left hand to the right of the midpoint. However, when these deviations were tested against zero (i.e. the objective midpoint) clear differences appeared related to hand, task and handedness. These results were discussed with respect to "enhancement theory".

Adult↗

PubMedDate not supplied

Is the optimal viewing position in reading influenced by familiarity of the letter string?

An optimal viewing position (OVP) for word recognition has been proposed by several authors. The location of this position would be located at the center of the word or just left of it. Several hypotheses ranging from perceptual to hemispheric factors have been proposed to explain this phenomenon. In the experiment presented here, the effect of the nature of the stimulus was tested: word, pseudo-word, or nonword on the existence and location of this position. Little research has investigated this issue. Five-letter words, pseudo-words, and non-words were presented, with the subject fixating initially on one of the five possible letter positions. The number of letters correctly identified and reading performance were recorded for each stimulus. Results show that an initial fixation on the third letter entails better letter identification for all kinds of stimuli. However, in terms of reading, only word reading benefit from a fixation on the third letter. These results are discussed in relation to the different hypotheses of OVP in reading. These are (1) hemispheric specialization, (2) reading habits, and (3) lexical constraints.

Adolescent↗

PubMedDate not supplied

Unilateral neglect: the effect of competing stimuli on estimated line length.

Normal subjects and patients with right hemisphere lesions with or without signs of left unilateral neglect judged the length of a horizontal line presented on the left or on the right side of space. In half of the trials, the line was presented with a centrally located square or diamond, and subjects had to identify the central stimulus before performing the judgment of length. The presence of the central stimulus improved accuracy of performance in controls and in patients without neglect; neglect patients, however, produced more overestimations of left-sided lines when these was presented with a central stimulus than when the lines occurred in isolation. This finding underlines the importance of attentional factors in length estimates performed by neglect patients in their neglected space.

Adult↗

PubMedDate not supplied

Position of the egocentric reference and performance in line bisection and subjective vertical estimation tasks.

Egocentric body coordinates such as the sagittal midline have been proposed to act as a reference for ballistic movements in extracorporeal space. Symmetrical functioning of the multiple neural structures processing sensory information would account for the normal sagittal position of the egocentric reference. According to this hypothesis a unilateral parietal lesion would induce a ipsilesional deviation which would prevent neglect patients from responding to stimuli that occur on that side. In this line of reasoning, an experimental manipulation of the position of the egocentric reference by way of a postural perturbation should have an effect on visuospatial tasks performance in normal subjects. Seventeen right-handed subjects were submitted in the dark to two visuomotor tasks: the adjustment of a luminescent rod to the vertical and the bisection of a luminescent line, either with the trunk and the head aligned at 0 degrees or with a 30 degrees trunk rotation to the right or to the left. Results revealed no significant effect of trunk rotation on the performance in both tasks. We discuss these findings and their implication for the understanding of the neglect syndrome.

Adult↗

PubMedDate not supplied

Correlation between the position of the egocentric reference and right neglect signs in left-brain-damaged patients.

Fourteen control subjects and thirty left-brain-damaged (LBD) patients with or without neglect performed a straight-ahead pointing task with their left hand while blindfolded. Results showed a significant correlation between the position of the egocentric reference and the presence of right neglect signs. We discuss here the egocentric hypotheses of spatial bias.

Adult↗