Sound localization in large mammals: localization of complex sounds by horses

The idea that large mammals localize sounds more accurately than small mammals has been noted frequently and is usually explained by reference to their large interaural distance and the correspondingly broad binaural time (delta t) and spectral (delta fi) differences between their two ears. Sound-localization thresholds for single clicks and 100-ms noise bursts were determined for horses, and the magnitude of the binaural time (delta t) and spectral (delta fi) cues for sound direction were measured on a horse. Although horses have relatively large interaural distances and physically broad binaural-localization cues available to them, their sound direction thresholds were markedly poorer than those of other large mammals--averaging 22 degrees for noise and 30 degrees for clicks. It appears that sound-localization acuity is not determined simply by the physical availability of binaural cues.