Background: Conjugate Lateral Eye Movements (CLEMs) may determine the extent of the relative activity of the two cerebral hemispheres during an on­going cognitive task. Several studies have documented more rightward CLEMs for verbal questions with left hemispheric activity and more leftward CLEMs for spatial questions with right hemispheric activity, while others have suggested CLEMs to be individualspecific independent of the questions. Thus previous findings are mixed and uncertain. This study questions the validity of CLEMs as a measure of functional laterality. Methods: The subjects were 400 healthy students in the age group 10­19 years. The subjects were required to orally respond to 10 verbal and 10 spatial questions. During each on­going cognitive process, the first observable CLEM direction was noted and categorised into rightward or leftward CLEM. Then whether this dependent on the type of question or was it an individual­specific stable trait was established. Results: In this study, majority of the subjects exhibited CLEMs pattern independent of the type of question (indicating subjects as either right­ or left­movers) and was statistically significant. There was no statistical significant difference between genders for the CLEMs pattern. Discussion: This suggests that the direction of gaze shift when people are thinking during different types of questions does not reflect the lateralization of underlying cerebral activity. This reflects that during an on­going cognitive task, CLEMs do not depend on preferential hemispheric activation, are independent of question type and is subjectspecific stable trait. Thus concluding that though CLEMs may have other neurophysiological implications, is not a valid index of functional laterality. The CLEMs pattern in future studies should be evaluated along with cerebral blood flow, positron emission tomography, etc.
Keywords: Conjugate Lateral Eye Movements; CLEMs; Functional Laterality; Verbal Questions; Spatial Questions; Cerebral Hemispheric Activation.