No description available.

Much of the research on differential hemispheric activation as a function of age or the presence of depression suggests that a relative decrease in left hemisphere activation is associated with depression, while a decrease of right hemisphere activation is associated with age. Recent research, however, has demonstrated the role of the right hemisphere in maintaining general behavioral arousal. Pilot data suggest that elderly people experience behavioral over-arousal when presented with stressful or novel environmental stimuli. Equally interesting is the finding in a single-case study that ambient light and noise have a differential effect on behavior presumed to be representative of the left and the right cerebral hemispheres. The left hemisphere appears to be more responsive to ambient light level, with the right hemisphere being more responsive to ambient noise level. The present study sought to provide further support of selective hemispheric activation to bright light, and to examine the relationships among hemi-activation, age and depression by using behavioral measures of lateral anterior (finger tapping rate) and posterior (dichotic listening) cortical functioning. Two identical experiments were employed to evaluate old and young, and depressed and non-depressed sUbjects. Direct evidence of right herni-aging effects on laterality was not significant in the first experiment, but data suggested the possibility of a ceiling effect for behavioral arousal in the older group which was not seen in younger subjects. The second experiment yielded no significant results between depressed and non-depressed groups. Hypotheses of under and over arousal in subjects are proposed to explain findings. Possible implications for treatment and recommendations for further research are proposed. / Ph. D.

Classical Stroop stimuli and newly developed face/word Stroop analog stimuli were used to investigate hemispheric interactions in Stroop interference effects (SEs) and corresponding event-related potentials (ERPs). Lateralized stimuli were presented unilaterally and bilaterally as congruent or incongruent color strip-word or face-word pairs (to invoke right hemisphere (RH) and left hemisphere (LH) specialization, respectively, in the latter case). The common finding for such tasks is that responses for the congruent condition are faster and more accurate than for the incongruent condition (i.e., the SE). A primary prediction is that the SE will be maximized when both the distractor and target components, or distractor alone, are presented to the specialized hemisphere (i.e., LH for words and RH for faces). A total of 88 right-handed University of North Texas students participated in one of four experiments. Participants manually responded to one component of the stimuli (i.e., color, face, or word), while ignoring the other. Behaviorally, participants showed a robust SE across all experiments, especially for the face/word task with word targets. Findings from the face/word Stroop analog tasks also indicated that SEs were produced by selective attention to either faces or words, implicating a role for top-down (controlled) processes. Hemispheric asymmetries were observed only for bilateral presentations of the face/word Stroop analog stimuli and did not differ for word versus face targets. The results suggest that the LH is less susceptible to interference from the RH than vice versa. Electrophysiologically, anterior N1 and P1, posterior P1 and N1, N2, and P3 components were identified. A SE was found for P3 amplitudes, but not latencies, across all four experiments such that the congruent condition generated greater amplitudes than the incongruent condition, suggesting that the P3 is an index of task difficulty. Surprisingly, SEs were also observed for the early ERP components, albeit embedded in higher order interactions. Taken together, the ERP evidence suggests that there is no single locus of the SE, and instead, the SE appears to be distributed over several stages of information processing.

No description available.

Abstract not available

Thesis (M.Communication pathology)-Universiteit van Pretoria, 2001.

No description available.

The general purpose of this study was to investigate the relationship between neuropsychological tests scores and perfusion deficits, based upon measures of regional cerebral blood flow (rCBF) taken from the single photon emission computed tomography (SPECT) scans of patients suffering from dementia of the Alzheimer type (DAT). The study was designed to determine if DAT patients categorized as having left hemisphere, right hemisphere, diffuse, or an absence of perfusion deficits, as measured by SPECT, would be accurately grouped into their respective categories, and if they would exhibit the corresponding neuropsychological deficiencies usually associated with lateral hemispheric asymmetries.Selected subjects were 80 right handed, DAT patients from the North Broward Medical Center - Memory Disorder Center, in Pompono Beach, Florida, who had been administered a neuropsychological test battery, and a SPECT scan.Through several ANOVA's that were calculated for each of the neuropsychological variables, it was concluded that DAT patients who suffered from perfusion deficits exhibited significantly lower levels of neuropsychological functioning than DAT patients without perfusion deficits.These analyses revealed significantly lower levels of neuropsychological performance in the perfusion deficit group on the combination of left hemisphere WAIS-R subtests (Information, Similarities & Vocabulary), WMS - Logical Story (p < .01), WRAT-R Reading, WRAT-R Mathematics, WMS Paired Associates, and the Rey Complex Figure (p < .05).A separate step-wise discriminant function analysis indicated that a combination of the neuropsychological variables could not accurately classify the DAT patients into their respective right hemisphere, left hemisphere, diffuse, or absence of perfusion deficit groups. The discriminant function classified only 32.5% of the grouped cases accurately. Of the original thirteen neuropsychological variables, only Paired Associates immediate recall of the WMS entered the discriminant analysis equation. This accounted for only 23% of the total variability that could be explained by differences between the perfusion deficit groups. In several post hoc ANOVA's using the Bonferroni method of multiple comparisons, it was revealed that the absence of perfusion deficit group scored significantly higher than the other groups on the majority of the left hemisphere neuropsychological measures. However, none of the right hemisphere neuropsychological measures attained significance. / Department of Educational Psychology

No description available.

Three reaction time experiments were conducted to determine when and how memory for the normal left-right orientation of letters is mediated by the developing brain. In each experiment, participants identified forward and backward letters presented unilaterally to each visual field and thus to each hemisphere (VF-H). / The main findings were as follows: (1) For the five-year-olds, no VF-H differences were found in the speed of identifying either forward or backward letters or in the difference in speed between forward and backward letters. (2) The seven-year-olds identified forward letters faster than backward letters in the right visual field-left hemisphere (RVF-LH) with the contralateral, right hand, and the boys, unlike the girls, also showed this difference in the left visual field-right hemisphere (LVF-RH) independent of the responding hand. (3) Performance of the nine-year-olds was similar to that of the seven-year-olds. (4) Adults identified forward letters faster than backward letters in the RVF-LH with each hand, whereas in the LVF-RH this difference was found for the ipsilateral, right but not for the contralateral, left hand. / Support was provided for the Corballis-Beale (1976) hypothesis, and discussion centered on the implications of the results for the development of cerebral lateralization of memory for the normal left-right orientation of letters in normal and reading disabled children.