Letter memory loads change more than visual-field advantage: interhemispheric coupling effects.

A derivation from Denenberg's (Denenberg, 1980. American Journal of Physiology, 238, R3-R13) model of brain organization is that significant correlations between left-hemisphere (LH) and right-hemisphere (RH) measures indicate that the hemispheres are coupled together in a general system. Two formally similar visual-field (VF) reaction-time (RT) tasks, one a LH-right (R) VF and the other a RH-left (L) VF advantage task, were performed by 30 female and 30 male right-handers under single-task (zero load) and dual task (three or six consonants in memory) conditions. Expected letter load effects upon VF performances were obtained. Particularly for RT variability, correlations of measures lateralized to different hemispheres (i.e., LVF-RVF, LH and RH tasks) increased linearly as load increased, while correlations of measures lateralized to the same hemisphere (i.e., two LH tasks) did not. Bihemispheric cortical activation may play a role in this general system coupling caused by complexity or load. Females demonstrated greater interhemispheric coupling.

The effects of voluntary lateral orienting on positive manifold for lateralized cognitive tasks.

As an extension of previous studies (Urbanczyk, Angel, & Kennelly, Brain and Cognition, 8, 206-226) examining the effects of unimanual tapping on lateralized cognitive tasks, lateral body orienting was added to an established dual task paradigm to generate differential hemispheric activation and shifts of attention. One hundred twenty right-handed university students retained sequences of digits or spatial locations for 20 sec either alone or during finger tapping. By turning head and eyes left or right, the hemisphere congruent with the sequences (LH for digits, RH for locations) or incongruent (vice versa) was activated. Activation had little effect on retention means but greatly affected resource composition, supporting task performance. Congruent orientation produced significantly higher positive correlations between digit and location tasks than incongruent orientation. Females showed higher sequence retention correlations than males across both orienting groups. For females, congruent activation enhanced tapping rates and tapping-retention task correlations. For males, activation affected neither of these. These results suggest that congruent attentional orienting may couple or integrate regions of the less activated hemisphere into networks of the more activated hemisphere. Greater inter- and intrahemispheric connectivity in the female cortex may produce a greater dependence upon a general attentional "resource."

Fatigue, depression, and cognitive performance among aged persons.

Previous research by the authors has suggested that older persons who are depressed may be especially susceptible to the effects of fatigue in situations where multiple skills are assessed. The impact of fatigue and the effects of depression on cognitive performance have long been recognized as impediments to the accurate assessment of competence in the aged. To investigate such influences, data were gathered from 72 aged persons who had been screened for depression and assigned to one of three conditions varying in effort and the fatigue-inducing nature of the tasks to be solved. Results suggested depressed persons were more prone to fatigue. For measures of both active and passive short-term memory, depression and task effort impacted on performance. Such effects were considerably weaker for measures of intelligence.

Hemispheric activation increases positive manifold for lateralized cognitive tasks: an extension of Stankov's hypothesis.

Stankov (1983a, Journal of Educational Psychology, 75, 471-490) suggests that the dual task paradigm, requiring the division of attention, increases positive manifold (i.e., positive intercorrelations) for cognitive tasks relative to the single task paradigm. Two dual task studies are reported. Unimanual finger-tapping served as the primary task and the short-term retention (20 sec) of digit or spatial-location sequences served as the secondary tasks. When both tasks were lateralized to the same hemisphere (digits and right-hand tapping or spatial locations and left-hand tapping), highest memory task intercorrelations (Experiment 1) and better retention of sequences (Experiments 1 and 2) resulted. Left-hand tapping produced more leftward looking and right-hand tapping more rightward looking (Experiment 2). Overflow from lateralized finger-tapping may shift the gradient of attentional activation toward the contralateral hemisphere, producing the homolateral gaze direction, the increase in positive manifold, and the better retention of sequences lateralized to that hemisphere.

Laterality of cerebral function: relations with anxiety, repression, and perception.

Based on two factor analyses of data from 67 right-handed undergraduates, a laterality quotient based on forward memory spans, spatial minus digit, divided by their sum, was devised. The hemispheric balance factor for which this quotient served as the principal marker had significant positive loadings by the laterality quotient for the Edinburgh Handedness Questionnaire and by a measure of repressive tendencies, the Marlowe-Crowne Social Desirability Scale. Scores from this factor were positively related to global as opposed to analytic perception as measured by the Navon tachistoscopic task. This factor was unrelated to the trait anxiety and working short-term memory factors which also emerged. Trait anxiety was negatively related to global perception. The results raise the possibility that greater degrees of right-handedness may be related to the release of the nondominant right hemisphere from inhibition and that working short-term memory may not be lateralized.

Depression and helplessness-induced cognitive deficits in the aged.

Sixty-six community-residing elderly (mean age = 72.5) were categorized as depressed (mean = 11.3) or nondepressed (mean = 3.9) based on Beck Depression Inventory scores. After a pre-test battery measuring short-term memory and crystallized/fluid intelligence, the subjects responded to a word association task, disguised as a test of interpersonal empathy, under response dependent or response independent reinforcement conditions, or were assigned to a no treatment control. A post-test battery of alternate forms followed. Four of seven measures showed significant pre- to post-test declines in performance. For two of these four, response dependent reinforcement prevented otherwise significant declines. With pre-test differences statistically controlled, depression produced significant post-test deficits in three measures. Response dependent reinforcement eliminated this depression deficit in one measure. The results indicate that depression may exacerbate fatigue effects for the elderly and response dependent reinforcement may prevent fatigue-caused deficits in short-term memory.