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Abstract
The auditory system creates a neuronal representation of the acoustic world based on spectral and temporal cues present at the listener's ears, including cues that potentially signal the locations of sounds. Discrimination of concurrent sounds from multiple sources is especially challenging. The current study is part of an effort to better understand the neuronal mechanisms governing this process, which has been termed “auditory scene analysis”. In particular, we are interested in spatial release from masking by which spatial cues can segregate signals from other competing sounds, thereby overcoming the tendency of overlapping spectra and/or common temporal envelopes to fuse signals with maskers. We studied detection of pulsed tones in free-field conditions in the presence of concurrent multi-tone non-speech maskers. In “energetic” masking conditions, in which the frequencies of maskers fell within the ±1/3-octave band containing the signal, spatial release from masking at low frequencies (∼600 Hz) was found to be about 10 dB. In contrast, negligible spatial release from energetic masking was seen at high frequencies (∼4000 Hz). We observed robust spatial release from masking in broadband “informational” masking conditions, in which listeners could confuse signal with masker even though there was no spectral overlap. Substantial spatial release was observed in conditions in which the onsets of the signal and all masker components were synchronized, and spatial release was even greater under asynchronous conditions. Spatial cues limited to high frequencies (>1500 Hz), which could have included interaural level differences and the better-ear effect, produced only limited improvement in signal detection. Substantially greater improvement was seen for low-frequency sounds, for which interaural time differences are the dominant spatial cue.
Highlights
The everyday acoustic environment is complex, in that multiple independent sound sources may be active at any given moment in time
Asynchronous, synchronous, all-pass, and band-pass conditions are shown in the various panels, low and high frequency ranges are indicated by colors, and all other energetic and informational masking conditions are indicated with various symbols
If we first focus on data obtained in the asynchronous timing condition for the all-pass and band-pass maskers (Fig. 5AB) we see that as before the all-pass informational masker (iR) masker resulted in little spatial release for either signal frequency since masked thresholds in the S0M0 configuration were already close to TQ
Summary
The everyday acoustic environment is complex, in that multiple independent sound sources may be active at any given moment in time. Since the number of individual sources is a priori unknown, segregation of sources in a mixture is a computationally ill-posed problem with infinite solutions. To solve this problem, the auditory system must employ heuristics in order to constrain the space of possible solutions. When two acoustic sources share some of these properties (cues) they tend to be grouped together and to be perceived as one auditory object (perceptual fusion). On the other hand, sources differ sufficiently from each other along the cue dimensions they will be segregated and will be perceived as distinct auditory objects (perceptual fission)
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