A Cardiac Measure of Cerebral Asymmetries in Infant Auditory Perception.

The utility of cardiac habituation/response recovery as a method for assessing infant cerebra! asymmetries in auditory perception on a dichotic listening test was studied. In a within-subjects design 12 3-month-old infants were given a series of four 10 trial tests during which their cardiac responses were habituated to a pair of dichotic speech syllables or music notes. The 10th trial in each test was a test trial on which one ear received its habituation stimulus while the other ear received a novel stimulus of the same type as the habituation pair (speech or music). Both stimulus type and ear receiving the novel stimulus were counterbalanced across tests. Overall, infants' cardiac responses habituated during the tests and in addition showed differential recovery to the novel stimuli. Specifically, greater response recovery occurred when a novel speech syllable was presented to the right ear than to the left ear. Conversely, greater response recovery was found when a novel music note was presented to the left ear than to the right ear. These results were taken as indicative that young infants show a pattern of auditory perceptual asymmetries much like that found in older children and adults and consistent with the theory that in man the left hemisphere is superior at processing speech and the right hemisphere superior with nonspeech sounds,