Relative Processing Demands Influence Cerebral Laterality for Verbal-Motor Integration in Persons with Down Syndrome

The study of cerebral specialization in the Down syndrome (DS) population has revealed an anomalous pattern of organization. In particular, dichotic-listening studies have suggested a left-ear/right hemisphere dominance for speech perception, whereas motor control research has revealed a left hemisphere dominance for executive-motor control. In the present investigation, we employed a recent adaptation of the dichotic listening procedure to examine interhemispheric integration during the performance of a lateralized verbal-motor task. Specifically, using the selective dichotic-listening procedure, participants were required to complete a rapid left or right hand pointing movement to one of two pictorial icons corresponding to the word presented to their precued ear. We observed that persons with DS (N = 17) and age-matched controls (N = 35) exhibited a right-ear advantage (REA) for our dichotic-aiming task. While these results appear to contradict previous dichotic listening studies, we propose that the manifestation of a lateral ear advantage in the DS population may have more to do with the response requirements of the task than with the characteristics or complexity of the stimulus material.