Impact of Spectrally Asynchronous Delays on Consonant Voicing Perception

Background: A possible voicing cue used to differentiate voiced and voiceless cognate pairs is envelope onset asynchrony (EOA). EOA is the time between the onsets of two frequency bands of energy (in this study one band was high-pass filtered at 3000 Hz, the other low-pass filtered at 350 Hz). This study assessed the perceptual impact of manipulating EOA on voicing perception of initial stop consonants, and whether normal-hearing and hearing-impaired listeners were sensitive to changes in EOA as a cue for voicing.

Purpose: The purpose of this study was to examine the effect of spectrally asynchronous auditory delay on the perception of voicing associated with initial stop consonants by normal-hearing and hearing-impaired listeners.

Research Design: Prospective experimental study comparing the perceptual differences of manipulating the EOA cues for two groups of listeners.

Study Sample: Thirty adults between the ages of 21 and 60 yr completed the study: 17 listeners with normal hearing and 13 listeners with mild-moderate sensorineural hearing loss.

Data Collection and Analysis: The participants listened to voiced and voiceless stop consonants within a consonant-vowel syllable structure. The EOA of each syllable was varied along a continuum, and identification and discrimination tasks were used to determine if the EOA manipulation resulted in categorical shifts in voicing perception. In the identification task the participants identified the consonants as belonging to one of two categories (voiced or voiceless cognate). They also completed a same-different discrimination task with the same set of stimuli. Categorical perception was confirmed with a d-prime sensitivity measure by examining how accurately the results from the identification task predicted the discrimination results. The influence of EOA manipulations on the perception of voicing was determined from shifts in the identification functions and discrimination peaks along the EOA continuum. The two participant groups were compared in order to determine the impact of EOA on voicing perception as a function of syllable and hearing status.

Results: Both groups of listeners demonstrated a categorical shift in voicing perception with manipulation of EOA for some of the syllables used in this study. That is, as the temporal onset asynchrony between low- and high-frequency bands of speech was manipulated, the listeners' perception of consonant voicing changed between voiced and voiceless categories. No significant differences were found between listeners with normal hearing and listeners with hearing loss as a result of the EOA manipulation.

Conclusions: The results of this study suggested that both normal-hearing and hearing-impaired listeners likely use spectrally asynchronous delays found in natural speech as a cue for voicing distinctions. While delays in modern hearing aids are less than those used in this study, possible implications are that additional asynchronous delays from digital signal processing or open-fitting amplification schemes might cause listeners with hearing loss to misperceive voicing cues.

Key Words

Assistive listening devices - hearing aids - speech perception