This paper presents a review of the main results of an application of discourse analysis in aphasics with the left hemisphere damages, and in the damaged (RHD) patients. Research findings indicate that aphasics have marked deficits on the level of microstructure, especially cohesion of discourse, whereas the coherence and superstructure of their texts are relatively well preserved. RHD patients show difficulties at the microstructure of discourse but not so marked as that of subjects. The main impairments of RHD patients' discourse can be observed at the level of text coherence. The both populations have also preserved cognitive representation concerned with script knowledge. Discourse processing at macrostructural level of discourse is affected in aphasics as well as in RHD patients. These results suggest that both hemispheres are necessary for normal discourse processes.
Cerebral lateralization in visual perception was investigated in 9 severe stuttering, 11 mild stuttering and 48 fluent speakers. The subjects were asked to identify words presented in the left or right visual field for 20 ms. Children responded by pointing to the exposed test word on a response card which contained four different words. Errors commited in the left and right visual fields were analyzed. The data showed a left hemisphere superiority in the processing of words in both the mild stutterers and the fluent speakers, but a right hemisphere advantage in the severe stutterers. The results suggest a close relationship between the severity of stuttering and functional brain organization.
The variability of simple actions with response to auditory stimuli was studied under different delay conditions. Subjects reacted as fast as possible or with a defined time delay (from 250 to 750 ms) to a tone switching off by pressing a response-key with the left index finger (controlled by the right hemisphere) or with the right one (left hemisphere). For short delays (requested response times below 350 ms) variability of responses was much larger then for longer delays (above 350 ms), especially for the right hand. Thus, precise temporal control on consciously mediated actions sets only in after a rather long delay (in some cases after half a second). Neuronal mechanisms underlying conscious temporal control of actions appear to be different for the two hemispheres.
Sex differenes in human brain lateralization are documented by studies on normal subjects, patients with the unilateral brain damage, and individuals with atypical level of hormones. However, there is no agreement as to the specific role of gender in the development of hemispheric asymmetry. This experiment was designed to examine whether gender identity plays an important role in the formation of brain lateralization, as some recent data seem to suggest. A group of subjects showing gender dysphoria transsexuals and two groups of control male and female subjects were presented with verbal and visual-spatial tasks. Results show that neither biological sex nor gender identity are sufficient factors to determine the pattern of hemispheric asymmetry.
In the present study a possible hemispheric asymmetry in size evaluation was tested. Subjects were presented with geometrical Vanderplas type figures of various sizes and shapes. The stimuli were exposed in paris, for 100 ms, one after another. The subject's task was to decide (by pressing one of three buttons) whether the second stimulus was the same as, smaller or bigger than the first one. The first stimulus in each pair was exposed unilaterally (randomly in the left or right visual field), and the second in the centre of the screen. Three different interstimulus intervals (ISI) were used: 50 ms, 500 ms, and 2,000 ms. The results showed shorter reaction times for left visual field presentation than for right visual field presentation at the 50 ms and 500 ms interstimulus interval. No laterality effect occured at the 2,000 ms ISI. The results indicate a right hemisphere predominance in stimulus size evaluation. Moreover, the suggest that hemispheric asymmetry is not a stable feature of the brain but is a synamic process that may change in the course of information processing.
JavaScript is turned off in your web browser. Turn it on to take full advantage of this site, then refresh the page.