On sound localization cues in the median plane

In order to make it clear which is more important for sound localization in the median plane, SP cues (spectral cues) or ID cues (interaural difference cues), two localization tests of sound sources simulated by a digital computer using measured individual head-related transfer functions (M. Morimoto et al., 9th ICA, H47 (1977)] were carried out. First, SP cues were presented to the subjects keeping interaural differences of all stimuli constant. Second, to the contrary, ID cues were presented to them keeping all spectra at one ear constant. The results of those tests are the following. (1) All subjects can localize stimuli with only SP cues. but they cannot localize so accurately as stimuli with the both cues. (2) They cannot localize stimuli with only ID cues at all. Those results show that SP cues are far more important than ID cues for sound localization in the median plane, however, that ID cues should not be neglected.