Spatial release from aerial masking in a harbor seal

Abstract

Spatial release from masking (SRM) occurs when a signal and masker are spatially separated, resulting in improvement of signal detection relative to when they are spatially coincident. Harbor seals feed in the water but haul out on land for a variety of activities. There have been no SRM investigations conducted on harbor seals in air. In this study, SRM was measured at 1, 8, and 16 kHz in a harbor seal (Phoca vitulina) who had to detect an aerial tone in the presence of an octave band of white noise centered at the tone frequency. While the masker always occurred in front of the subject (0 deg), the tone occurred at 0, 45, or 90 deg in the horizontal plane. Absolute thresholds were also measured at these angles to account for differences in hearing sensitivity based on source azimuth. Current data show that the largest masking level differences (MLDs) of 7 dB occurred at 1 kHz when the signal was projected at 90 deg. MLDs reported here on an amphibious carnivore are larger than those measured under water, are consistent with measurements collected on terrestrial animals, and have important implications for noise effects on free-ranging animals.