Effect of hemispherectomy on frequency difference limens for the two ears

Abstract

Hemispherectomized subjects display a strong ear dominance for the pitch mixture of dichotic chords: The tone presented to the ear ipsilateral to the removed hemisphere is less salient in the dichotic sound image than is the contralateral ear tone [R. Efron, M. Dennis, and J. E. Bogen, J. Acoust. Soc. Am. 60, Suppl. No. 1, 550 (1976)]. Two possible causes for similar ear dominance seen in normal subjects are an asymmetry in the transducer properties of the two ears or an asymmetry in the way two basically symmetrical inputs are combined centrally [E.W. Yund and R. Efron, J. Acoust. Soc. 62, 607–617 (1977)]. Evidence for the former derives from the finding that the dominant ear tends to have a superior frequency resolving capacity [P.L. Divenyi, R. Efron, and E.W. Yund, J. Acoust. Soc. Am. 62 624–632 (1977)]. Evidence for the latter derives from the present experiments which show that, in hemispherectomized subjects, there is no difference between the frequency dl in the two ears. The results suggest the existence of an efferent pathway from the cortex which can influence the way pitch information from the two ears is combined (weighted). [Work supported by the Veterans Administration.]