Multitask investigation of individual differences in hemispheric asymmetry.

Abstract

Right-handed subjects (N = 120) participated in four different laterality tasks designed to measure aspects of cerebral hemisphere asymmetry: identification of dichotically presented consonant-vowel syllables (CVs), examination of the effects of concurrent repetition of CVs and concurrent anagram solution on finger-tapping by the right and left hands, lateralized identification of CVs presented tachistoscopically to the left and right visual fields, and left/right biases on a free-vision face task involving judgments of emotion. Ear differences in the dichotic listening task were related to the pattern of lateralized interference in the dual-task finger-tapping paradigm. There were no other significant relations between pairs of tasks, but when the present results are considered in the light of other recent experiments, there appears to be a relation between lateral bias on the free-vision face task and visual field differences in tachistoscopic identification. The pattern of results has implications for hypothesized individual differences among right-handers in cerebral dominance for verbal processes, input pathway dominance, and asymmetric arousal of the two cerebral hemispheres.

Categorization versus distance: Hemispheric differences for processing spatial information

“…Although there is more variability in cerebral laterality (including laterality for verbal processes) among righthanders than was once suspected (e.g., Hellige, Bloch, & Taylor, 1988;Levineet al, 1987;Levyet al, 1983aLevyet al, , 1983b, the inclusion of left-handed subjects would increasethe variation significantly. For this reason, it would alsobe useful to include left-handers in subsequent studies of individual differences.…”

“…When investigating such individual differences, it is desirable to order tasks in the same way for all subjects so as to hold any order and carryover effects constant (cf. Hellige, Bloch, & Taylor, 1988). To minimize such effects, the testing sessions were separated by 48 h. Note that the task performed second might benefit from practice with the task performed first or might suffer from fatigue or negative transfer for those stimuli assigned to different response keys in the two tasks.…”

“…Furthermore, recent studies (e.g., Hellige, Bloch, & Taylor, 1988;Levine, Banich, & Kim, 1987;Levy, Heller, Banich, & Burton, 1983a, 1983b suggest considerable individual variation among right-banders in the direction and magnitude of cerebral laterality for a variety of verbal and nonverbal tasks. In view of this variability and in view of Kosslyn' s (1987) results for right-handed versus ambidextrous subjects, the present experiment tests the hypothesis that right-handers who show a relatively large laterality effect for one task also show a relatively large laterality effect in the opposite direction for the other task.…”

Interhemispheric transfer and the processing of foveally presented stimuli

“…allocation, reading habits, and the like [ 11,24,31,34]. So, it might be argued that the findings with foveal and parafoveal vision correlated for reasons unrelated to cerebral dominance and interhemispheric transfer.…”

“…Each subject finished two series of 288 stimuli. The clock face reading test was included to assert that the VHF asymmetries of the first two tasks were not due to attentional biases of the subjects in favor of one or the other VHF, and/or to differences in the speed between the afferent pathways of the two hemifields [31,34]. A positive lambda, which can vary from -oo to + oc, just like a positive point-biserial correlation index, indicates a RVF superiority, a negative lambda index represents a LVF superiority.…”