Dolphins (Tursiops truncatus) use multiple auditory mechanisms for detecting tonal signals in natural and anthropogenic noise

Abstract

The dolphin's ability to detect a 10 kHz tone masked by a variety of noise types was measured using a standard band-widening paradigm. Maskers included natural noise (rain, snapping shrimp, and ice squeaks), anthropogenic noise (pile saw and boat propeller cavitation) and statistical noise (Gaussian and comodulated noise). For most noise types, detection thresholds increased as noise bandwidth increased up to 1 kHz (the dolphin's critical bandwidth at 10 kHz). Masking patterns for narrow-band maskers were similar regardless of the masker type. However, for noise bandwidths greater than 1 kHz, masking patterns diverged by as much as 23 dB depending on the noise type. The power spectrum model provided reasonable predictions for Gaussian, rain, pile saw, and boat noise masking patterns. Additional experiments suggested that mechanisms related to temporal envelope processing (across-channel envelope comparison and within-valley listening) determined masking patterns for snapping shrimp and comodulated noise. Thresholds in ice squeak noise, which proved to be the most effective masker, were related to the dolphin's inability to discriminate the signal from the background noise rather than inability to detect the signal. These results suggest that the dolphin auditory system uses multiple mechanisms for signal detection in complex noise [Work supported by the ONR.]