Release from auditory masking with complex signals and complex noise in the bottlenose dolphin ( Tursiops truncatus )

Dolphins are social animals that rely heavily on passive and active acoustics for communication, navigation, foraging, and detecting predators. Auditory masking, from both natural and anthropogenic noise sources, may adversely affect these fitness-related capabilities. The dolphin's ability to detect a variety of complex signals (both dolphin phonations and tonal signals) masked by Gaussian, comodulated, snapping shrimp, and ice squeaks noise was tested. Detection thresholds were measured using a go/no-go adaptive staircase procedure. Masking patterns were similar for all signals (whistles, burst-pulse, and pure tones) except for click signals. Masking from ice squeaks resulted in the largest masked thresholds, while snapping shrimp and comodulated noise resulted in a release from masking relative to thresholds from Gaussian noise. Click signals were most difficult to detect when masked by snapping shrimp. Recognition thresholds were estimated for whistle-like signals using a cross-modal, matching-to-sample procedure. Recognition thresholds were on average 4 dB greater than detection thresholds for all noise types. The auditory mechanisms governing the results are discussed. [Work supported by the ONR.]