Index of content:
Volume 120, Issue 3, September 2006
- SPEECH PERCEPTION 
120(2006); http://dx.doi.org/10.1121/1.2221390View Description Hide Description
Previous psychophysical studies have shown that the perceptual distinction between voiceless fricatives and affricates in consonant-vowel syllables depends primarily on frication duration, whereas amplitude rise slope was suggested as the cue in automatic classification experiments. The effects of both cues on the manner of articulation between /ʃ/ and /tʃ/ were investigated. Subjects performed a forced-choice task (/ʃ/ or /tʃ/) in response to edited waveforms of Japanese fricatives /ʃi/, /ʃu/, and /ʃɑ/. We found that frication duration, onset slope, and the interaction between duration and onset slope influenced the perceptual distinction. That is, the percent of /ʃ/ responses increased with an increase in frication duration (experiments 1–3). The percent of /ʃ/ responses also increased with a decrease in slope steepness (experiment 3), and the relative importance between slope portions was not even but weighted at onset (experiments 1 and 2). There was an interaction between the two cues of frication duration and steepness. The relative importance of the slope cue was maximum at a frication duration of (experiment 3). It is concluded that the frication duration and amplitude rise slope at frication onset are acoustic cues that discriminate between /ʃ/ and /tʃ/, and that the two cues interact with each other.
120(2006); http://dx.doi.org/10.1121/1.2221405View Description Hide Description
The simple up-down adaptive procedure is a common method for measuringspeech reception thresholds. It is used by the Dutch speech-in-noise telephone screening test [National Hearing test; Smits and Houtgast Ear Hear.26, 89–95 (2005)]. The test uses digit triplets to measure the speech reception threshold in noise by telephone. About people took this test within four months of its introduction and details were stored of all individual measurements.Analyses of this large volume of data have revealed that the standard deviation of estimates increases with hearing loss. This paper presents a calculation model which—using an intelligibility function as input—can determine the standard deviation of estimates and the bias for the simple up-down procedure. The effects of variations in the slope of the intelligibility function, the guess rate, the starting level, the heterogeneity of the speechmaterial, and the possibilities of optimizing measurements were all explored with this model. The predicted decrease in the standard deviation of estimates as a result of optimizing the speechmaterial was confirmed by measurements in 244 listeners. The paper concludes by discussing possibilities for optimizing the development of comparable tests.