Volume 103, Issue 3, March 1998
Index of content:
- SPEECH PERCEPTION 
Effects of local speaking rate context on the perception of voice-onset time in initial stop consonants103(1998); http://dx.doi.org/10.1121/1.421297View Description Hide Description
This study explored the prediction that local speaking rate context affects the perception of voice-onset time (VOT) in initial stop consonants not only for ambiguous stimuli at the category boundary, but also for good exemplars from the category center [Volaitis and Miller, J. Acoust. Soc. Am. 92, 723–735 (1992)]. Naturally produced exemplars of the voiceless phonetic category were presented in the context of syllables produced at fast or slow speaking rates in a series of perceptual tasks, including phonetic discrimination, identification, and goodness rating. The results from all three tasks revealed no effects of speaking rate context on the perception of VOT in initial stop consonants. Rather, it appears that listeners perceive longer VOTs as better exemplars of the voiceless phonetic category, irrespective of the rate context. Further, an additional condition, in which the instructions and familiarization tasks presented prior to the administration of the perceptual tests were similar to those used by Volaitis and Miller [J. Acoust. Soc. Am. 92, 723–735 (1992)], revealed that the previous results may have been influenced by the experimental design.
103(1998); http://dx.doi.org/10.1121/1.421264View Description Hide Description
Thresholds for formantdiscrimination of female and male vowels are significantly elevated by two stimulus factors, increases in formant frequency and fundamental frequency [, J. Acoust. Soc. Am. 100, 2462–2470 (1996)]. The present analysis systematically examined whether auditory models of vowel sounds, including excitation patterns, specific loudness, and a Gammatone filterbank, could explain the effects of stimulus parameters on formant thresholds. The goal was to determine if an auditory metric could be specified that reduced variability observed in the thresholds to a single-valued function across four sets of female and male vowels. Based on -Port [J. Acoust. Soc. Am. 99, 3770–3781 (1996)], four critical bands around the test formant were selected to calculate a metric derived from excitation patterns. A metric derived from specific loudness difference (ΔSone) was calculated across the entire frequency region. Since analyses of spectra from Gammatone filters gave similar results to those derived from excitation patterns, only the 4-ERB (equivalent rectangular bandwidth) and ΔSone metrics were analyzed in detail. Three criteria were applied to the two auditory metrics to determine if they were single-valued functions relative to formant thresholds for female and male vowels. Both the 4-ERB and ΔSone metrics met the criteria of reduced slope, reduced effect of fundamental frequency, although ΔSone was superior to 4-ERB in reducing overall variability. Results suggest that the auditory system has an inherent nonlinear transformation in which differences in voweldiscrimination thresholds are almost constant in the internal representation.