Spectral contrast effects in vowel categorization by listeners with sensorineural hearing loss

Abstract

The auditory system is highly sensitive to changes in acoustic input. This is especially true for sounds with relatively stable (reliable) spectral properties across time. Over a limited range, changes to the spectrum (e.g., spectral peak location upon introduction of a new sound) are perceptually enhanced in proportion to the property's long-term reliability, producing spectral contrast effects (SCEs). For example, a neutral vowel between /i/-/e/ is more likely to be labelled /e/ (high-F1) when preceded by sounds with a reliable low-frequency peak in the F1 range for /i/, and vice versa. Yet, it is unknown how SCEs affect speech perception by hearing-impaired (HI) listeners because research has only examined normal-hearing (NH) listeners. Here, listeners with mild-to-moderate HI identified target vowels varying from /i/-/e/ that followed a precursor sentence. Reliability of precursor spectral peaks was manipulated using low-F1 or high-F1 bandpass filters with +5 to +20 dB gain. SCE magnitude was proportional to precursor filter gain (like NH listeners), and surprisingly, to the amount of low-frequency hearing loss. Thus, mechanisms responsible for SCEs are not dependent on healthy hearing, and are magnified by auditory filter broadening associated with sensorineural hearing loss. Implications of these findings for speech perception will be discussed.