Bilateral field interactions, hemispheric specialization and evoked potential interhemispheric transmission time

Abstract

The interrelationship between bilateral visual field processing, hemispheric specialization and interhemispheric transmission time (IHTT) was examined in two experiments in order to test two theories regarding callosal function and lateralized visual processing. Contrary to both theoretical speculations [Braun, Neuropsychology Review, Vol. 3, pp.321–365, 1992] and a recent report [Nowicka et al. Neuropsychologia, Vol. 34, pp. 147–151, 1996], the directional asymmetry in evoked potential measures of IHTT did not vary with task differences in indices of hemispheric specialization. IHTT was faster from right to left hemispheres regardless of visual field advantage for the task. Similarly, patterns of correlation between IHTT and bilateral field advantage did not change between verbal and spatial matching tasks, despite differences in visual field advantage. Since the latter data did not consistently support the Brown and Jeeves [ Neuropsychologia, Vol. 31. pp. 1267–1281, 1993] hypothesis, an alternative hypothesis involving hemispheric asymmetries in attention rather than processing specialization was proposed.