Age effects in identifying and localising dichotic stimuli: a corpus callosum deficit?

In the present study, dichotic listening performance of 31 older adults was compared with performance of 25 younger adults under free and focussed attention conditions. In addition to an age-related general decrease in performance, we observed in the focussed attention condition increased asymmetry in the elderly group: the decrease of recall performance was stronger for the left ear (LE) than for the right ear (RE), while the increase of localisation errors was greater for the RE than for the LE. Identifying and localising digits appear to be different processes mediated predominantly by the left and right hemisphere, respectively. Since age-related reduced performance is strongest for the ear ipsilateral to the hemisphere dominant to that particular function, these findings may be ascribed to decline of corpus callosum functioning resulting in decreased interhemispheric interaction rather than to a selective decline of right hemisphere functions.