High-frequency auditory filter shapes in an Atlantic bottlenose dolphin

Abstract

High-frequency auditory filter shapes were calculated for a 20-year-old female Atlantic bottlenose dolphin (Tursiops truncatus). Thresholds were determined for tones of 40, 60, 80, and 100 kHz masked by notched noise. Auditory filter shapes were determined by fitting the integral of the roex(p,r) filter shape to the functions relating masked tonal threshold to notch width. Filter shapes were found to be approximately symmetric at the moderate noise level used. Equivalent rectangular bandwidths of the auditory filters ranged from 16% of center frequency at 40 kHz to 11% of center frequency at 100 kHz. There was very little change in the bandwidths of the filters between 60 and 100 kHz, indicating that relative tuning sharpness increases as a function of frequency in this range. Efficiency of processing after the periphery was found to be maximal at 40 and 60 kHz (better than 12-dB SNR) and to decrease gradually above 60 kHz. The efficiency estimates allowed for the reanalysis of critical ratio data collected previously for the same animal; the bandwidth estimates from the present and earlier study were found to be in good agreement.