Are hemispheric strategy differences independent of the level of performance?

Studies requiring identification of consonant-vowel-consonant (CVC) nonwords have suggested that attention is distributed more slowly or sequentially across the letters when they are presented to the right hemisphere than to the left hemisphere. Two experiments investigated whether hemispheric differences in processing strategy would be reduced with reductions of hemispheric differences in accuracy. The magnitude of visual field differences in accuracy was controlled by manipulating exposure duration, and the effect was observed on visual field differences in processing strategy. For both CVC identification (Experiment 1) and identification of nonletter symbols (Experiment 2), hemispheric strategy differences were independent of differences in accuracy. Both quantitative and qualitative hemispheric differences in processing visual displays appear to depend on the nature of the stimuli and the nature of the processes they invoke.

Effects of bilateral stimulation and stimulus redundancy on interhemispheric interaction.

Recent visual laterality studies have included trials in which critical stimulus information is presented simultaneously in both visual half-fields and, thereby, simultaneously to both cerebral hemispheres. To investigate interhemispheric interaction, researchers compare performance on bilateral redundant trials with performance on unilateral trials in which a single copy of the target is presented to one hemisphere or the other. The authors used the identification of nonword letter trigrams to examine the relationship between unilateral and bilateral performance when the 2 types of trials were equated for the number of locations stimulated (Experiment 1) and the number of redundant copies of the target (Experiment 2). Results suggest that when the number of stimulated locations is held constant, each of 2 copies of a target stimulus can be processed with the same efficiency and the same strategy as it would have been had it been the only copy.

Behavior of adult and aged mice before and after central injection of interleukin-1beta.

The level of locomotor activity, body temperature (T(B)), and feeding for adult (3-5-month old) and aged (22-24-month old) male BALB/c mice was determined and the sensitivity of the two age groups to the anorectic, febrile, and behavioral properties of interleukin-1beta (IL-1beta) in the brain was examined. Baseline locomotor activity and T(B) were markedly lower in aged mice than in adults and the circadian rhythm for both activity and T(B) were disrupted in the aged. Adult and aged mice consumed similar amounts of food during the daytime and nighttime, but aged mice made longer, less frequent visits to the feed cup. To determine if aging affects the responsiveness to central IL-1beta, adult and aged mice were injected intracerebroventricularly with PBS or IL-1beta. Compared to age-matched PBS controls, IL-1beta increased T(B) in both adult and aged mice. The peak deltaT(B) was greater in aged mice than in adults, but because of a lower baseline T(B) in aged mice, peak T(B) after IL-1beta was not different between groups. Locomotor activity of aged mice receiving PBS was about half that of PBS-injected adults and was not depressed further by IL-1beta. However, compared to age-matched PBS controls, centrally administered IL-1beta depressed food intake more in aged mice than in adults. These data indicate that even though feeding, locomotor activity, and T(B) are affected by aging, the central component of the inflammatory response mediated by IL-1beta is retained.