Perception of dichotic chords by hemispherectomized subjects

Abstract

The phenomenon of ear dominance for the pitch of dichotically presented tones has been described in previous publications [Efron and Yund, Neuro-psychologia 12, 249–256 (1974); 13, 137–150 (1975); 13, 151–161 (1975); Brain and Language 3, 246–254 (1976); J. Acoust. Soc. Am. 59, 889–898 (1976)]. In these studies on more than 100 normal subjects, the pitch mixture of the perceived dichotic chord was strongly dominated by the frequency presented to the right ear in 10% and by the left ear frequency in another 10%. The remaining subjects (80%) had either a weak or a nonsignificant ear dominance. Subsequent studies on subjects with forebrain commissurotomy [J. Acoust. Soc. Am. 59, S53(A) (1976)] indicated that the pitch minute of the dichotic chord was determined by a functional asymmetry in a subcortical pitch processor. The present study with three subjects hemispherectomized in infancy and one at age 13 reveal a strong ear dominance for the ear contralateral to the existing hemisphere in all four subjects. These results suggest that there is efferent control, from the cerebral cortex, on the hypothesized subcortical pitch processor.