Relationship of lateral eye movements recorded in the dark to verbal and spatial question types

The role of the cerebellum in 'real' and 'imaginary' line bisection explored with 1-Hz repetitive transcranial magnetic stimulation

The role of the cerebellum is well characterized for many motor processes and for some cognitive tasks, although its contribution to lateralized spatial judgement has never been probed directly. To address this omission, we investigated the effects of cerebellar disruption on two different line bisection tasks in eight healthy subjects. Based on previous evidence of crossed cerebellar-cortical connections we predicted a shift in the perceived midline that would occur in opposite directions depending on the cerebellar hemisphere targeted. Repetitive transcranial magnetic stimulation (rTMS), given at 1-Hz (600 pulses), was used as a non-invasive way to interfere with processing in the cerebellar cortex. Performance was assessed for both 'physical' line bisection using a newly developed Landmark variant task and for 'mental' line bisection using number pairs. The effects for number line bisection were lateralized--left but not right cerebellar rTMS increased rightward errors, whereas for physical line bisection rTMS to either hemisphere did not affect performance. Effects due to neck muscle contraction and changes in eye position were ruled out with appropriate control stimulation sites, and eye-tracking. The results confirm the role of the cerebellum in spatial judgement, and, for the first time, demonstrate direct cerebellar involvement in the generation of the midline in 'imaginal' (number) space. The difference between number line and physical line bisection effects is discussed with reference to pre-existing models of cerebellar hemispheric specialization and functional topography.

Cognitive consequences of asymmetrical visual distraction

The authors explored whether manipulating the location of distraction in the participants' visual field influences the degree of competition between visual and other cognitive processes. If a cognitive task is lateralized to a particular hemisphere, visual distraction directed toward that same hemisphere should impair performance on that task more than should visual distraction directed toward the other hemisphere. Consistent with this hypothesis, the authors found in Experiments 1 and 2 that participants better recalled words of high imageability in a verbal memory task when the examiner was in the participant's left visual field (right hemisphere) than when the examiner was in the participant's right visual field (left hemisphere). In Experiment 3, the authors found that this effect reversed for performance on a right-hemisphere spatial task.

Lateral motion bias associated with reading direction

We found that when Americans view ambiguous lateral long-range apparent motion, they exhibit a robust bias to experience leftward movement. In successive experiments, right-handers and left-handers, and left-side drivers from Japan equally manifested this leftward bias. However, bilingual viewers whose first language reads from right to left exhibited no lateral bias. Furthermore, the bilingual sample produced a significant correlation between exposure to English and extent of leftward motion bias. The findings provide strong evidence that reading habits can influence directionality in motion perception.

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.