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 focused attention conditions. In addition to an age-related general decrease in performance, we observed in the focused attention condition increased asymmetry in the elderly group: the decrease of recall performance was stronger for the left ear (LE) then for the right ear (RE), while the increase of localisation errors were greater for the RE than for LE. Identifying and localising digits appear to be different process 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 finding may be ascribed to decline of corpus callosum functioning resulting in decrease interhemispheric interaction rather than to a selective decline of right hemisphere functions.