Abstract
Spatial release from masking (SRM) occurs when spatial separation between a signal and masker decreases masked thresholds. The mechanically-coupled ears of Ormia ochracea are specialized for hyperacute directional hearing, but the possible role of SRM, or whether such specializations exhibit limitations for sound source segregation, is unknown. We recorded phonotaxis to a cricket song masked by band-limited noise. With a masker, response thresholds increased and localization was diverted away from the signal and masker. Increased separation from 6° to 90° did not decrease response thresholds or improve localization accuracy, thus SRM does not operate in this range of spatial separations. Tympanal vibrations and auditory nerve responses reveal that localization errors were consistent with changes in peripheral coding of signal location and flies localized towards the ear with better signal detection. Our results demonstrate that, in a mechanically coupled auditory system, specialization for directional hearing does not contribute to source segregation.
Highlights
Natural soundscapes are composed of numerous biotic and abiotic sound sources (Brumm and Slabbekoorn, 2005; Theunissen and Elie, 2014)
Test stimuli consisted of a 76 dB SPL 4 s burst of band-limited masker in combination with a 2 s target signal broadcast at different intensities to result in varied signal-to-noise ratios (SNRs) (Figure 1B)
Ormia ochracea responded with greater walking distances, consistent response latencies, and localized the target signal with improved accuracy in the absence of a masker
Summary
Natural soundscapes are composed of numerous biotic and abiotic sound sources (Brumm and Slabbekoorn, 2005; Theunissen and Elie, 2014). Coherent representations of various sources are derived from the composite waveform and signals of interest are segregated from other competing sound sources (McDermott, 2009) In humans, this sensory challenge is known as the ‘cocktail party problem’ and it describes difficulties encountered in perceiving speech in noisy social settings (Bregman, 1990; Bronkhorst, 2000; Brumm and Slabbekoorn, 2005; Cherry, 1953; Hulse, 2002; McDermott, 2009). Some insect choruses are known to produce sustained levels of background noise (Gerhardt and Huber, 2002; Romer, 2013) These choruses are often composed of mixed species with communication signals that may share spectral, temporal, and spatial overlap. Such background noises have the potential to negatively impact the performance of auditory systems in perceiving relevant signals (Brumm, 2013; Brumm and Slabbekoorn, 2005; Wiley, 2015)
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