Tactile discrimination of direction of lines in relation to hemispheric specialization

Hemispheric Asymmetry in Olfaction on a Category Judgement Task

An olfactory experiment using a category-judgement paradigm is reported. Right-handed women showed a right-nostril superiority in identifying five intensity levels of n-butanol. The results are seen as supporting Pendse's (1978) hypothesis that hemispheric specialization for language and visuospatial functions can be accounted for in terms of an information transmission model.

The Finger-Tip Numberwriting Test: Practice Effects versus Lateral Asymmetry

By counterbalancing hand order, both practice effects and lateral asymmetry were measured on the Finger-tip Numberwriting test together with 5 other tactile tests of finger-tip writing and finger identification administered to 32 right-handed adults averaging 41 yr. of age. Under counterbalanced hand-order conditions, the Finger-tip Numberwriting test showed no lateral asymmetry, but a significant practice effect. In contrast, the same subjects showed a left-hand advantage on nonverbal detection of tactile line direction, indicating normal right-hemispheric superiority. Normal Finger-tip Numberwriting performance likely involves integration of specialized processing capacities in both cerebral hemispheres. The results do not invalidate the standardized Finger-tip Numberwriting test as a clinical tool but demonstrate the value of manipulating independent variables when standardized clinical neuropsychological tests are applied to questions in experimental research.

The contributions of vision and haptics to reaching and grasping

This review aims to provide a comprehensive outlook on the sensory (visual and haptic) contributions to reaching and grasping. The focus is on studies in developing children, normal, and neuropsychological populations, and in sensory-deprived individuals. Studies have suggested a right-hand/left-hemisphere specialization for visually guided grasping and a left-hand/right-hemisphere specialization for haptically guided object recognition. This poses the interesting possibility that when vision is not available and grasping relies heavily on the haptic system, there is an advantage to use the left hand. We review the evidence for this possibility and dissect the unique contributions of the visual and haptic systems to grasping. We ultimately discuss how the integration of these two sensory modalities shape hand preference.

Stress-level cortisol treatment impairs inhibitory control of behavior in monkeys

Most studies of cortisol-induced cognitive impairments have focused on hippocampal-dependent memory. This study investigates a different aspect of cognition in a randomized placebo-controlled experiment with monkeys that were treated with cortisol according to a protocol that simulates a prolonged stress response. Young adult and older adult monkeys were assigned randomly to placebo or chronic treatment with cortisol in a 2 x 2 factorial design (n = 8 monkeys per condition). Inhibitory control of behavior was assessed with a test shown previously in primates to reflect prefrontal cortical dysfunction. Failure to inhibit a specific goal-directed response was evident more often in older adults. Treatment with cortisol increased this propensity in both older and young adult monkeys. Age-related differences in response inhibition were consistent across blocks of repeated test trials, but the treatment effects were clearly expressed only after prolonged exposure to cortisol. Aspects of performance that did not require inhibition were not altered by age or treatment with cortisol, which concurs with effects on response inhibition rather than nonspecific changes in behavior. These findings lend support to related reports that cortisol-induced disruptions in prefrontal dopamine neurotransmission may contribute to deficits in response inhibition and play a role in cognitive impairments associated with endogenous hypercortisolism in humans.

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.

Cerebral and sex differences in the categorization of haptic information

This study investigated the extent to which each cerebral hemisphere categorizes stimuli varying in texture and shape. Eighteen right-handed subjects, nine males and nine females, rated the perceived dissimilarity between pairs of stimuli presented to both hands and to the right or left hand, with haptic noise in the contralateral hand. Results suggest a right hemisphere competence in the categorization of both texture and shape information. Furthermore, males showed better separation of categories for stimuli presented to both hands only.

Neuropsychological assessment of a case of early right hemiplegia: qualitative and quantitative analysis

Evidence for normal development of linguistic but poor visuo-perceptual skills has been obtained with the neuropsychological assessment of a case of early left-brain injury. Data suggest the transfer of linguistic functions from the left to the right hemisphere at the expense of visuo-perceptual capacities for which the right hemisphere is potentially specialized.