Localization of noise bands by Old World monkeys.

The acuity of auditory localization in Old World monkeys (Macaca) was determined psychophysically for 44 noise bands graded in bandwidth and center frequency. The acuity of localization was assessed through the method of constant stimuli under free-field conditions in an anechoic chamber. Monkeys were trained through positive-reinforcement operant-conditioning procedures to report a change in azimuth of the signal by releasing a response disk. The results show that localization thresholds are dependent upon the bandwidth of the signal over much of the macaque's range of audibility. Thresholds for the detection of a change in location varied from 18 degrees (for a signal 250 Hz in bandwidth centered at 11 200 Hz) to 4 degrees (for a signal 8000 Hz in bandwidth centered at 8000 Hz). The results suggest that the localization of spectrally complex signals is determined by a mechanism sensitive to periodicity (time-domain) information across the monkey's range of audibility.