Consonant identification under maskers with sinusoidal modulation: Masking release or modulation interference?

Abstract

The present study investigated the effect of envelope modulations in a background masker on consonant recognition by normal hearing listeners. It is well known that listeners understand speech better under a temporally modulated masker than under a steady masker at the same level, due to masking release. The possibility of an opposite phenomenon, modulation interference, whereby speech recognition could be degraded by a modulated masker due to interference with auditory processing of the speech envelope, was hypothesized and tested under various speech and masker conditions. It was of interest whether modulation interference for speech perception, if it were observed, could be predicted by modulation masking, as found in psychoacoustic studies using nonspeech stimuli. Results revealed that masking release measurably occurred under a variety of conditions, especially when the speech signal maintained a high degree of redundancy across several frequency bands. Modulation interference was also clearly observed under several circumstances when the speech signal did not contain a high redundancy. However, the effect of modulation interference did not follow the expected pattern from psychoacoustic modulation masking results. In conclusion, (1) both factors, modulation interference and masking release, should be accounted for whenever a background masker contains temporal fluctuations, and (2) caution needs to be taken when psychoacoustic theory on modulation masking is applied to speech recognition.

Sentence recognition in noise promoting or suppressing masking release by normal-hearing and cochlear-implant listeners

“…This is not surprising as modulation interference rarely occurs in NH listeners unless there is substantially decreased redundancy in the speech signal such as restrictions or manipulation of spectral or temporal information (Kwon and Turner, 2001). On the other hand, CI listeners are subject to modulation interference due to reduced spectral representations of speech signals and their increased reliance on envelope modulation cues, which could potentially be disrupted by fluctuating maskers.…”

“…Furthermore, in cochlear implant (CI) users, masking release is largely absent (Nelson et al, 2003;Stickney et al, 2004;Loizou et al, 2009). In fact, the possibility for the opposite phenomenon has been suggested (Kwon and Turner, 2001). In this "modulation interference," performance is poorer in fluctuating than in steady backgrounds.…”

Masking Release and Modulation Interference in Cochlear Implant and Simulation Listeners

“…Without fine-grained spectral information in speech, listeners might rely more on temporal cues to process consonants and vowels. In the presence of modulated noise, such temporal information in speech is obscured by the noise modulations, and NH-Sim and CI listeners may experience modulation interference rather than (or in addition to) masking release (Kwon & Turner, 2001). As a result, little to no masking release has been observed from these groups of listeners.…”

“…We hypothesized that, if NHSim and CI listeners rely more on the temporal envelope cues of speech, then masking interference may be strongest when the noise is amplitude modulated at these rates. Although studies on both NH-Sim and CI listeners (Ihlefeld et al, 2010;Kwon & Turner, 2001;Nelson et al, 2003;Qin & Oxenham, 2003) examined the effect of modulation rate on speech perception, no clear answers were reported. We hypothesized that NH-Sim and CI listeners would show no masking release but might show masking interference when the noise is amplitude modulated at a rate approaching the syllable rate.…”

“…One thing in common found from the previous studies of speech perception in noise was the positive SNRs used for CI or NH-Sim listeners (e.g., Fu & Nogaki, 2004;Kwon & Turner, 2001;Nelson et al, 2003;Qin & Oxenham, 2003;Stickney et al, 2004). Because these listeners were listening to impoverished spectral speech cues, they were tested at favorable (positive) SNRs in which the signal and noise are more similar in level in order to avoid a floor effect (Nelson et al, 2003).…”