Measuring the auditory phase response based on interaural time differences

Abstract

Harmonic complexes are often used as maskers for measuring the cochlear phase response. The phase curvature can affect the masking in order of up to 20 dB, an effect known as the masker-phase effect. There is evidence that signals yielding peaky internal masker representations after passing the cochlear filter produce minimum masking, with the fast-acting cochlear compression as the main contributor to that effect. Thus, in hearing-impaired listeners showing reduced or absent compression, the estimation of phase response using the masking method may be difficult. Here, an alternative method is proposed, which is based on the effect of signal peakedness on the sensitivity to interaural time differences (ITD) in the signal envelope. With the two methods, ITD and masking thresholds were measured, respectively, in seven normal-hearing listeners. The stimuli were 300-ms Schroeder-phase harmonic complexes, ranging from 3400 to 4600 Hz with a 100-Hz fundamental frequency, with the signal phase curvature varied between −1 and 1. The lowest ITD thresholds were observed for phase curvatures that produced minimum masking. This suggests that the ITD method is a promising candidate for estimating the cochlear phase response in hearing-impaired listeners.