Subjects made timed manual responses in judging whether laterally presented four-letter words were identical to targets. In Experiment 1, nontargets differed by a single letter from targets. A right-field superiority occurred only for targets (which were detected fastest of all) and for nontargets where a letter changed at Position 2 or Position 3. Changes at initial and final positions were detected faster than the two middle positions, and there were no significant field differences. In Experiment 2, ascenders and descenders were controlled and changes were made in nontargets at all four letter positions, at Positions 1 and 4, at Positions 2 and 3, or at 2 alone. Response times for nontargets varied inversely with the number of differing letters, regardless of position. Significant field differences again only appeared for changes in the two middle positions. Letters at the beginning and end of a word seem to be processed faster than and differently from those within, where field differences are strongest. Vowel-consonant differences probably do not account for these effects, which are more compatible with some form of parallel, rather than either serial or holistic, processing.

Many species have difficulty in discriminating between mirror-image stimuli, especially those about a vertical axis, and when identificatory rather than purely perceptual processes are involved. Various theories are reviewed. In two experiments involving same-different judgments for pairs of stimuli, triangles or semicircles, these were simultaneously presented either unilaterally or bilaterally, and in mirror or aligned orientations with respect to each other. Mirror oriented stimuli presented to opposite cerebral hemispheres were no more readily matched than those possessing the same orientations (aligned), thus suggesting that at the perceptual level there is no interaction between mirror-corresponding points in the two visual cortices. Foreknowledge of stimulus orientations failed differentially to affect the findings. Two other studies were performed involving manual identification of single letters, correct or mirror oriented, in either visual field. Here, for most subjects, mirror reversal proved either less disruptive or even advantageous when in the visual field which is normally inferior with correctly oriented material. It was concluded that mirror-image confusion at the level of memory is almost certainly a consequence of reversed coding, in some form, in the opposite sides of the brain. A number of incidental findings were made with respect to visual field effects.

No abstract

The dichotomies verbal/visuospatial, serial/parallel and analytic/holistic are reviewed with respect to differences in hemispheric processing. A number of experimental parameters may be varied in such tasks, and together with certain frequently-occurring weaknesses of experimental design may account for the often discrepant results hitherto reported. The above factors are systematically reviewed, and three further experiments are reported which attempt to fill in the missing designs. Further evidence is given in support of the hypothesis that right-hemisphere superiority is most apparent in processes leading to identity matching. It is quantitative rather than qualitative, and may depend upon operations on the entire gestalt, such as holistic matching, mental rotation, reflection, distortion, etc., rather than, e.g., simultaneous (parallel) processing of discretely analysed or isolated features or elements. On the other hand left-hemisphere involvement in visuospatial processing is thought to reflect analysis of the configuration into its separable components; such processing may be either serial or parallel, and may frequently lead to a judgement different.

Pairs of outline profiles were successively presented in a tachistoscope either to the same or opposite visual fields and in the same or mirror-reversed orientations. Reaction times and errors were recorded for both same and different judgments. Mirror-reversed material was not processed as readily as sameoriented material. However, the decrement resulting from mirror reversal was not nearly as great when the faces went to opposite, as compared with same, hemispheres. This was considered as partial support for the theory of symmetrization of interhemispheric traces. Separate input to each hemisphere was found to result in performance as good as when both stimuli went to the same one. Same judgments were faster as found in similar studies; a possible explanation is considered.