SOUND LOCALIZATION IN CHINCHILLAS .2. FRONT BACK AND VERTICAL LOCALIZATION/

The ability of chinchillas to make front/back and vertical locus discr iminations was examined behaviorally using a conditioned avoidance pro cedure. Their minimum audible angle for localizing single broadband no ise bursts was 36 degrees for front/back localization and 23 degrees f or vertical localization. Sound localization tests using filtered nois e demonstrated that the signal must contain high frequencies in order for chinchillas to make front/back and vertical locus judgements and t hat frequencies in their highest audible octave (i.e., above 16 kHz) c ontribute to localization. These results support the view that a major selective advantage of high-frequency hearing in mammalian evolution was its utility for monaural as well as binaural sound localization.