Hemispheric differences for feature detection.

The role of hemispheric processing for visual features was explored by tachistoscopically presenting subjects with stimulus displays composed of the letter I, displays in which a single T was embedded in an array of I's, or displays in which the letter O was embedded in an array of I's. The number of array elements was also manipulated (4, 16, or 36) to assess the effects of display size on featural detection for each visual field. Subjects verbally indicated whether array elements were all the same, or whether a T or O was present. Hemispheric error rates varied as a function of the type of letter to be detected, with left-hemisphere presentations producing superior performance for the detection of T's, right-hemisphere presentations yielding superior performance for the detection of O's, and Same displays demonstrating hemispheric patterns consistent with these results. The findings suggest that the analysis of perceptual features during visual stimulus processing may determine hemispheric outcomes in a variety of task situations.

Hemispheric differences for orthographic and phonological processing.

The role of hemispheric differences for the encoding of words was assessed by requiring subjects to match tachistoscopically presented word pairs on the basis of their rhyming or visual similarity. The interference between a word pair's orthography and phonology produced matching errors which were differentially affected by the visual field/hemisphere of projection and sex of subject. In general, right visual field/left hemisphere presentations yielded fewer errors when word pairs shared similar phonology under rhyme matching and similar orthography under visual matching. Left visual field/right hemisphere presentations yielded fewer errors when word pairs were phonologically dissimilar under rhyme matching and orthographically dissimilar under visual matching. Males made more errors and demonstrated substantially stronger hemispheric effects than females. These patterns suggested visual field/hemispheric differences for orthographic and phonological encoding occurred during the initial stages of word processing and were more pronounced for male compared to female subjects.