Auditory sensitivity of seals and sea lions in complex listening scenarios

Abstract

Standard audiometric data, such as audiograms and critical ratios, are often used to inform marine mammal noise-exposure criteria. However, these measurements are obtained using simple, artificial stimuli-i.e., pure tones and flat-spectrum noise-while natural sounds typically have more complex structure. In this study, detection thresholds for complex signals were measured in (I) quiet and (II) masked conditions for one California sea lion (Zalophus californianus) and one harbor seal (Phoca vitulina). In Experiment I, detection thresholds in quiet conditions were obtained for complex signals designed to isolate three common features of natural sounds: Frequency modulation, amplitude modulation, and harmonic structure. In Experiment II, detection thresholds were obtained for the same complex signals embedded in two types of masking noise: Synthetic flat-spectrum noise and recorded shipping noise. To evaluate how accurately standard hearing data predict detection of complex sounds, the results of Experiments I and II were compared to predictions based on subject audiograms and critical ratios combined with a basic hearing model. Both subjects exhibited greater-than-predicted sensitivity to harmonic signals in quiet and masked conditions, as well as to frequency-modulated signals in masked conditions. These differences indicate that the complex features of naturally occurring sounds enhance detectability relative to simple stimuli.

Auditory object perception: A neurobiological model and prospective review

“…deer, elk) (Lingle and Riede, 2014) and even aquatic mammals such as pinnipeds (e.g. walruses, seals) (Cunningham et al, 2014; Reichmuth and Casey, 2014). Note, however, that some emotional calls, especially distress vocalizations, appear to reflect evolutionary conserved mechanisms underlying both production and behavioral responses (Lingle et al, 2012).…”

Source level measurements for harbor seals and implications for estimating communication space

“…Furthermore, conventional methods for predicting masking are often based on average noise levels over the duration of the target signal, which may not be appropriate for noises that vary significantly in time. Prior work has shown that the classic application of critical ratio data to predict masking in realistic listening scenarios is valid in some cases and inaccurate in others (see, e.g., Erbe and Farmer, 2000;Erbe, 2002;Jensen et al, 2009;Branstetter et al, 2013;Dooling et al, 2013;Cunningham et al, 2014). The extent to which this conventional method can be reasonably applied to evaluate hearing in marine mammals in the presence of impulsive noise remains unclear.…”

Shipping noise in a dynamic sea: a case study of grey seals in the Celtic Sea

“…Calculations were carried out for 125Hz since it is one of two 1/3-octave bands (63 and 125Hz) proposed to be monitored by MSFD and is believed to be within the hearing range of pinnipeds such as grey seals (Kastak & Schusterman, 1998;Cunningham et al, 2014).…”