Alpha asymmetry as a function of cognitive mode: the role of lateral eye movements

Conjugated lateral eye movements and EEG: a study on schizophrenic and depressive patients

Lateral gaze aversions which follow reflective or thought provoking questions are called conjugated lateral eye movements (CLEMs). This response was studied in 20 schizophrenic patients, 20 depressive patients and 20 healthy controls. Frontal and parietal EEG measures were recorded simultaneously with the question/answer task. There were no differences in CLEMs among the 3 groups. Schizophrenic and depressive patients demonstrated a significantly reduced EEG-power on the left and an increased power on the right in comparison with healthy controls. This may point to a functional interhemispheric ‘disconnection’ in patients. Comparative correlations revealed EEG-power increase during the occurrence of contralateral CLEMs in the whole 10 min task.

Influence of lateral gaze on electroencephalographic spectral power

The effects of maintaining lateral gaze (as opposed to looking straight ahead) on electroencephalographic spectral power were tested in 12 right handed male subjects during eye opening (EO) and eye closure (EC). Our working hypothesis, based on Kinsbourne's paradigm, was that maintaining right lateral gaze activates the left hemisphere while maintaining left lateral gaze activates the right hemisphere, this activation resulting in a reduction in the spectral power over the hemisphere in question. Results showed that the variations in spectral power involved mainly the alpha frequency band. In the EC condition, the results were consistent with our working hypothesis: right lateral gaze produced a marked reduction in left hemispheric spectral power. In the EO condition, alpha power was constantly higher in the right hemisphere whether lateral gaze was maintained to the right or to the left. This can possibly be due to an attentional effect. Results are discussed with regard of the type of alpha rhythm and of the activation of cortical oculomotor centres. They shed light on the controversy concerning the existence of specific EEG correlates of cognitive activity, which preferentially involve each of the cerebral hemispheres.

Lateral preference and neuropsychological correlates of schizotypy

A battery of 11 schizotypy questionnaires was administered to 316 male undergraduates. The scores of the 266 white subjects were subjected to a principal components analysis, and 73 subjects scoring at the upper and lower ends of the factor score distribution based on the first unrotated component were recalled for neuropsychological testing. The battery of neuropsychological tests consisted of four tests of motoric performance, four subtests from the Wechsler Adult Intelligence Scale-Revised, the conjugate lateral eye movement test, and a lateral preference questionnaire. Subjects high on schizotypy did not differ from low scorers on overall neuropsychological performance or performance asymmetries. High scorers did show a sinistral shift in hand and foot preference and more crossed dominance compared with controls. Asians scored significantly higher than whites on several schizotypy scales, raising the question of a possible ethnic bias in these measures.

Oculomotor activity and the alpha rhythm

From the beginning of clinical use of the EEG until now a close connection with oculomotor activity was assumed and empirically proven. After giving a sketch of the historical development, the issue is extended to the question of a connection between task-related alpha asymmetries and oculomotor activity. In doing so, the concepts of attention and cognition/emotion have to be dealt with. Referring to Kinsbourne, a conceptual framework is outlined which allows a mediation of the different methodical perspectives and thereby the formulation of testable hypotheses.

Conjugate lateral eye movements: a second look

It has been suggested that conjugate lateral eye movements (CLEM) are related to cerebral lateralization. Two types of research have developed: studies examining individual differences (hemisphericity) and studies examining the type of questions used to elicit eye movements (hemispheric specialization). In a 1978 review, Ehrlichman and Weinberger questioned the notion that CLEM is related to cerebral lateralization, particularly with regard to individual differences. However, since their review, a substantial number of studies have been published which are pertinent to the validity of CLEM. The following paper reviewed the validity of CLEM through three avenues, neurophysiological evidence, relationships with other measures of laterality and relation to spatial and verbal stimuli. Overall, it was concluded that there is sufficient evidence to support the CLEM model. Converging evidence from studies on EEG, electrical stimulation, ablation, brain damage, sodium amytal testing, blood flow, positron emission tomography, dichotic listening, and visual half fields was found to be, for the most part, supportive. The results for verbal and spatial task performance were mixed. Studies examining verbal abilities or a verbal to spatial comparison were generally supportive. The findings for spatial abilities alone were more equivocal. Evidence on question-type was found to be weak but positive, with about half the studies showing the predicted asymmetry and the other half reporting nonsignificant results. The implications of an interaction between hemisphericity or characteristic arousal and hemispheric specialization were also discussed.

Adults' mental rotation of spatial information: effects of age, sex and cerebral laterality

The mental rotation ability of young (mean age = 25.3) and elderly adults (mean age = 65.3) was assessed. Preferred cerebral hemisphere for information processing was determined by asking subjects questions designed to elicit lateral eye movements. Subjects were classified as preferring the right hemisphere, the left hemisphere, or neither hemisphere (mixed dominance). Participants were then given a task requiring them to match rotated blocks used in the Shepard and Metzler [13] experiment. Young subjects were more accurate than elderly subjects and males were more accurate than females at both age levels. There was no difference in accuracy as a function of preferred hemisphere for information processing. It was concluded that: (1) there may be no relationship between preferred hemisphere for processing and accuracy on a mental rotation task (2) there are age-related changes in the accuracy of mental rotation, and (3) males perform more accurately than females throughout adulthood on mental rotation tasks.