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Detection in noise by spectro-temporal pattern analysis
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1984
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Nonsimultaneous masking and across‑frequency temporal pattern analysis provide the theoretical backdrop for the study. The study aims to investigate how comodulation masking release enables signal detection at low signal‑to‑noise ratios. The authors tested a 400‑ms, 1000‑Hz tone in band‑limited noise with coherent envelopes, attributing improved detectability to use of energy outside the critical band when envelope characteristics match. In random noise, detection thresholds rise with bandwidth up to a critical bandwidth and then plateau, whereas with envelope‑coherent noise thresholds fall when bandwidth exceeds the critical band, and the position of coherent flanking bands does not affect the unmasking magnitude.
Detectability of a 400-ms, 1000-Hz pure-tone signal was examined in bandlimited noise where different spectral regions were given similar waveform envelope characteristics. As expected, in random noise the threshold increased as the noise bandwidth was increased up to a critical bandwidth, but remained constant for further increases in bandwidth. In the noise with envelope coherence however, threshold decreased when the noise bandwidth was made wider than the critical bandwidth. The improvement in detectability was attributed to a process by which energy outside the critical band is used to help differentiate signal from masking noise, provided that the waveform envelope characteristics of the noise inside and outside the critical band are similar. With flanking coherent noise bands either lower or higher in frequency than a noise band centered on the signal, it was next determined that the frequency relation and remoteness of the coherent noise did not particularly influence the magnitude of the unmasking effect. An interpretation in terms of nonsimultaneous masking was reconciled with some aspects of the data, and with an interpretation in terms of across-frequency temporal pattern analysis. This paradigm, in which detection is based upon across-frequency temporal envelope coherence, was termed ‘‘comodulation masking release.’’ Comodulation offers a controlled way to investigate some of the mechanisms which permit signals to be detected at adverse signal-to-noise ratios.