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Journal of Speech and Hearing Research Vol.39 4-18 February 1996.
© American Speech-Language-Hearing Association
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Labelling and Discrimination of a Synthetic Fricative Continuum in Noise

A Study of Absolute Duration and Relative Onset Time Cues

Craig Formby 1
Donald G. Childers 2

Ajit L. Lalwani 2
1 Division of Otolaryngology-HNS Department of Surgery University of Maryland School of Medicine Baltimore
2 Department of Electrical Engineering University of Florida Gainesville

Categorical perception was evaluated for a nine-token voice onset time (VOT) continuum with endpoint tokens /feil/-/veil/. The synthetic speech continuum was presented in a random-level noise masker at different signal-to-noise ratios (SNR=0, +6, +12 dB) and overall presentation levels (50 and 70 dB HL). Overall labelling performance deteriorated as the SNR was reduced. Labelling results for the +12-dB-SNR condition reflected a category boundary at 87 ms for listeners with normal hearing sensitivity. The companion two-step discrimination function revealed better-than-chance performance between pairs of tokens labelled fail, chance performance between pairs of tokens labelled vail, and a slight performance peak at the labelling boundary between fail and vail. Listeners with high-frequency audiometric deficits produced labelling results for the +12-dB-SNR condition that were similar to normal functions measured for the 0-dB-SNR condition. These listeners were unable to discriminate two-step differences in voicing duration, but they produced a normal temporal labelling boundary. To try to understand the noncategorical discrimination data, a psychoacoustic analog for the speech continuum was evaluated. Relative onset time (ROT) difference limens (DLs) were measured as a function of the temporal onset delay of a low-frequency sawtooth waveform relative to the onset of a high-frequency noise burst. The ROT cue was used only when absolute stimulus duration could not be relied upon as a consistent cue, under conditions where a large range of random overall duration was presented to the listener. The ROT DLs were relatively invariant over a range of standard delays from 50 to 110 ms. The average DL was about 30 ms, which is consistent with the small performance peak in the synthetic speech discrimination function.

KEY WORDS: synthetic speech perception, masking, fricatives, noise-induced hearing loss, temporal acuity

Submitted on June 29, 1994
Accepted on August 14, 1995


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