Changes in masked thresholds of a harbour seal ( Phoca vitulina ) associated with angular separation of signal and noise sources

• Published in: Canadian Journal of Zoology
• Main Author: Turnbull, S. D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1994
• Subjects: Animal Science and Zoology; Ecology, Evolution, Behavior and Systematics; harbour seal; Phoca vitulina
• Online Access: http://dx.doi.org/10.1139/z94-253; http://www.nrcresearchpress.com/doi/pdf/10.1139/z94-253

The masked pure tone thresholds of a harbour seal (Phoca vitulina) were measured at various angles using a white noise masker. The white noise source was placed at 0°, 30°, 60°, and 90° relative to the midline of the seal's head (0°). The masked pure tone thresholds for each angle were determined at 2, 4, 8, and 16 kHz. As the angle separating the signal and noise sources increased from 0° to 90°, the critical ratios of the harbour seal decreased by 1–4 dB. This shift in masked thresholds from a reference point of 0° azimuth was significant (H = 10.374, df = 3,16, p < 0.05). No significant difference was found in masked thresholds between 0° and 30° or between 60° and 90°. This indicates that if a noise source is separated by more than 30° relative to the location of a vocalizing seal, signal detection thresholds will be enhanced and communication distances increased.