It has been hypothesized that the brain computes two different kinds of spatial-relation representations: one used to assign a spatial relation to a category and the other used to specify metric distance with precision, The present visual half-field experiment offers support for this distinction by showing that the left and right cerebral hemispheres make more effective use of the categorization and metric distance representations, respectively. Furthermore, the inclusion of a bilateral stimulus presentation condition permits the computation of a reversed association that offers additional support for the distinction between two types of spatial-relation representation. Kosslyn (1987) has hypothesized that the human brain computes two different kinds of spatial-relation representations. One type of representation is used to assign a spatial relation to a category, such as "outside of' or "above," whereas the other type of representation preserves location information using a metric coordinate system in which distances are specified effectively. One way to obtain converging information about the plausibility of the distinction between these two processing subsystems is to show that they have different neurological substrata. With this in mind, Kosslyn has suggested that the left cerebral hemisphere makes more effective use of the categorization processing subsystem and that the right cerebral hemisphere makes more effective use of the metric distance processing subsystem. The present experiment was designed to provide tests of this lateralization hypothesis.On each trial of the present experiment, the subjects were shown a stimulus consisting of a horizontal line and a small dot in one of 12 possible locations (6 above the line and 6 below the line). During different experimental sessions, each subject performed a categorization task and a distance judgment task using these stimuli. Stimuli on different trials were presented to the right visual field-left hemisphere (RVF-LH) or the left visual field-right hemisphere (LVF -RH). It was of particular interest to determine whether or not there would be a task x visual field interaction (a processing dissociation, as discussed by Hellige, 1983, and Zaidel, 1983) and whether the interaction would be of the form predicted by Kosslyn's (1987) hypothesis. Because the stimuli and responses are identical for the categorization and distance-judgment tasks of the present experiment, any such interaction must The research reported here was supported in part by Research Grant BNS-8608893 from the National Science Foundation. The authors thank Alice Healy, Stephen Kosslyn, and two anonymous reviewers for helpful comments on an earlier draft of this manuscript. Correspondence may be sent to Joseph B. Hellige, Department of Psychology, University of Southern California, Los Angeles, CA 90089-1061. reflect differences in the processing subsystems required rather than other differences related to stimulus input (cf. .During the categorization task, the subjects were required to ind...

Corpus callosum abnormalities in psychopathic antisocial individuals may reflect atypical neurodevelopmental processes involving an arrest of early axonal pruning or increased white matter myelination. These findings may help explain affective deficits and previous findings of abnormal interhemispheric transfer in psychopathic individuals.

Right-handed Ss identified consonant-vowel-consonant (CVC) nonsense syllables presented tachistoscopically. The CVC on each trial was presented to the left visual field-right hemisphere (LVF-RH), to the right visual field-left hemisphere (RVF-LH), or the same CVC was presented to both visual fields (bilateral presentation). When recognition was incorrect, the pattern of errors was qualitatively different on LVF-RH and RVF-LH trials, suggesting that each cerebral hemisphere has its own preferred mode of processing the CVC stimuli. The qualitative pattern of errors on bilateral trials was identical to that obtained on LVF-RH trials. The bilateral results are described well by a model that assumes the mode of processing characteristic of the RH dominates on bilateral trials but is applied to both the LVF-RH and RVF-LH stimuli.

Functional hemispheric asymmetries were examined for right- or left-handed men and women. Tasks involved (a) auditory processing of verbal material, (b) processing of emotions shown on faces, (c) processing of visual categorical and coordinate spatial relations, and (d) visual processing of verbal material. Similar performance asymmetries were found for the right-handed and left-handed groups, but the average asymmetries tended to be smaller for the left-handed group. For the most part, measures of performance asymmetry obtained from the different tasks did not correlate with each other, suggesting that individual subjects cannot be simply characterized as strongly or weakly lateralized. However, ear differences obtained in Task 1 did correlate significantly with certain visual field differences obtained in Task 4, suggesting that both tasks are sensitive to hemispheric asymmetry in similar phonetic or language-related processes.

Two experiments examined the effect of concurrently holding 0, 2, 4, or 6 nouns in memory on the recognition of visual stimuli briefly presented to the left or right visual fields. When stimuli to be visually recognized were complex visuospatial forms it was found that a relatively easy memroy load of 2 or 4 nouns improved visual recognition accuracy on right visual field (left-hemisphere) trials relative to the no-memory condition; however, a more difficult memory load of 6 nouns decreased visual recognition accuracy to a level slightly below the no-memory condition. There were no effects of concurrent verbal memroy on visual form recognition on left visual field (right-hemisphere) trials. When the stimuli to be visually recognized were words it was found that a relatively easy memroy load of 2 or 4 nouns improved visual recognition accuracy and a more difficult load of 6 nouns decreased visual recognition accuracy on both left and right visual field trials. The complete pattern of results indicates that several factors including cerebral hemisphere specialization, stimulus codability, selective perceptual orientation, and selective cerebral hemisphere interference interact in systematic ways to produce overall visual laterality effects.