Individual differences in perceptual closure at the phoneme level

Abstract

The amount of acoustic information available from the speech signal was reduced by removing all regions of the waveform in which the rms amplitude fell below a threshold value. This removal was accomplished by envelope center clipping followed by attenuation and envelope expansion. The processing was carried out independently in three-frequency bands, which were then recombined. The result was intended to simulate the effects of hearing loss with recruitment. Phoneme recognition in consonant–vowel–consonant words was measured in eight normally hearing subjects as a function of threshold. Subjects, essentially, heard the top x dB of the speech signal, where x varied from 3–30 dB. Significant individual differences of performance were found, covering a range of ±3.6 dB when measured in terms of the threshold required for a score of 50%. Because all subjects in this experiment had access to the same sensory evidence, the findings support a perceptual closure explanation of individual differences. It may be, therefore, that some of the individual differences of phoneme-level speech perception by the hearing impaired, or by normals listening in noise, also reflect differences in the ability to complete perceptual closure. [Research supported by NIDCD.]