Measurement of the dichotic listening ear advantage for intersubject and interstimulus comparisons.

Conventional dichotic listening techniques can unquestionably be used for nominal (left vs. right) categorization of ear or hemispheric differences. These techniques cannot, however, be used for ordinal comparisons of the size of ear advantages among different subjects or different tasks if the measure of the size of the lateral asymmetry is confounded with effects of varying overall performance, attentional bias, or choice of laterality index. A psychophysical procedure is described which is designed to avoid these confounds by measuring discrimination ability, in decibels, as the interaural intensity difference (IID) required for a specific accuracy. Results from two experiments with right-handed subjects showed an average right-ear advantage of about 3 db for phoneme discrimination and an average left-ear advantage of the same size for intonation discrimination.