Sex-related differences in functional human brain asymmetry: verbal function - no; spatial function - maybe

Somatoperceptual asymmetry for cognitive stimuli: support from experimental and clinical observations

Two studies, one experimental with intact-brain subjects (Study I), and one clinical with left or right hemisphere-damaged and non-neurological general medical patients (Study II), were conducted to examine somatolateral asymmetry in the recognition of verbal (letter) and visuospatial (nonsense shapes) stimuli. Blindfolded subjects were required to explore two stimuli dichhaptically, and were instructed to haptically identify the target stimulus in a set of test stimuli. The findings of Study I indicated that fewer trials were required to recognise nonsense shapes when they were presented to the left hand, whereas fewer trials were required for letters when they were presented to the right hand. The findings of Study II indicated that performance of the hand ipsilateral to the damaged left hemisphere was better for nonsense shapes than for letters, and performance of the hand ipsilateral to the damaged right hemisphere was better for letters than for nonsense shapes.

Perceptual asymmetries in the somatosensory system: a dichhaptic experiment and critical review of the literature from 1929 to 1986

Dichhaptic matching of 3-D nonsense shapes was used to assess sex-specific differences in haptics. In an initial object exploration/description phase, strategy was manipulated with instructions to encode each object using either a visual image (which was drawn) or verbal description (tape recorded). These drawings or tape recordings were subsequently used on their own to identify each object. Attempts were made to maintain similarity between the verbal and spatial procedures, to avoid methodological biasing of hand superiorities (e.g., the same number of alternatives and the same presentation times were used). Differences in hand superiority did not, however, result. To obtain a broader perspective, a critical review table was compiled of the entire somatosensory asymmetry literature. Clear patterns emerged for all types of task when results potentially stemming from methodological biases and those based on only certain levels of samples were excluded. Somatosensory perceptual asymmetries are not robust, although hand superiorities are in the predicted direction when they do occur; nevertheless, we find little support for sex-specific asymmetries in these studies. Dichhaptic presentations lack the efficacy of other somatosensory (as well as tachistoscopic) tasks overall, possibly because of the time scale necessary for free haptic exploration.

Sex differences in the cognitive effects of unilateral brain damage: comparison of stroke patients and normal control subjects

Our original paper on the influence of the sex of the patients on the cognitive effects of unilateral brain damage mainly described the differences found between the various lesion groups (left/right, male/female) and said little about comparisons between these groups and our control subjects. Such comparisons are examined here; they confirm that the major sex differences after such brain damage appear in tasks intended to involve nonverbal processing. This evidence supports the hypothesis that women, to a greater extent than men, may employ verbal, left hemisphere processing to solve ostensibly nonverbal problems.