Hemispheric Dominance Shifts in Processing a Varying Complexity Spatial Task.

Abstract

Physiological differences have been thought to account for the left hemisphere's superiority at verbal, sequential processing while the right hemisphere is better at visuospatial, holistic processing. However, when task complexity and resulting strategy changes are taken into account such a strict definition of function appears overly simplistic. The task chosen for this experiment was hypothesized to quantitatively vary the amount of spatial processing involved. With such a task the relationship between right and left hemispheric performance can be assessed at varying levels of task difficulty. This allows the comparison of two models which explain differential hemispheric reaction times. According to the interhemispheric transfer time explanation one hemisphere is dominant and the non-dominant hemisphere always transfers information to the dominant hemisphere causing increased reaction time. The other model hypothesizes bilateral processing of unequal efficiency with the less efficient hemisphere taking longer. Subjects were 22 familial right h and ed males from introductory psychology classes. Lateralized pairs of patterns, which were displayed on a video monitor for 25 msec, were judged as being identical or mirror images of each other. The pair elements were rotated either 0(DEGREES), 60(DEGREES), 120(DEGREES) or 180(DEGREES) from each other, thus varying the amount of spatial processing involved. Reaction times, accuracy and confidence ratings were recorded by an Apple computer. The hypothesis for this task that subjects would rotate mental representations of stimuli until they are in the same orientation was supported by increasing reaction times associated with increasing degrees of rotation for "same" judgments. An overall right visual field superiority was observed for "same" judgments. The reverse finding at 180(DEGREES) suggests that as stimuli are rotated by increasing amounts there is apparently a quantitative change, but in addition a qualitative difference in processing at 180(DEGREES). This was probably due to the subject selecting an alternate strategy for making his judgment. Visual field reaction time differences were found to increase significantly for 0(DEGREES) to 60(DEGREES) and from 60(DEGREES) to 120(DEGREES), thus supporting a bilateral processing of unequal efficiency interpretation of the findings. An interhemispheric transmission time explanation of differential hemispheric reaction times would predict constant differences for increased rotations.