Perception of dichotic chords by split-brain subjects

Abstract

An ear dominance for pitch information has been described for dichotic chords [R. Efron and E. W. Yund, Neuropsychologia 12, 249–256 (1974); 13, 137–150 (1975); 13, 151–161 (1975); Brain and Lang. 2 (1976) (in press)]. This work has shown that a subject's ear dominance for pitch has no correlation with his ear dominance for dichotic consonant-vowel (CV) syllables or his handedness. In addition, the ear dominance is unaffected by attempts to attend to one or the other ear and the subject's performance is characterized by unusually low variance. This array of characteristics suggests that the asymmetry is introduced at subcortical levels. Ear dominance for the pitch of dichotic chords in split-brain subjects was determined using a verbal response (testing the left hemisphere), a right-hand response (testing the left hemisphere), and a left-hand response (testing the right hemisphere). The psychometric curves in each subject were identical for the three modes of report indicating that each hemisphere displays the same ear dominance, i.e., if a subject was right-(or left-) ear dominant for dichotic chords both hemispheres were equally so. On the other hand, all the split-brain subjects had an overwhelming right-ear dominance for dichotic CV's , as previously described [B. Milner, L. Taylor, and R. W. Sperry, Science 161, 184–186 (1969). These results suggest that the same imbalance of pitch information is received by both hemispheres as a result of an asymmetry in a subcortical central pitch processor.