Lateralized speech perception with small interaural time differences in normal-hearing and hearing-impaired listeners

Spatial release from masking (SRM) elicited by interaural timing differences (ITDs) only can be almost normal for listeners with symmetrical hearing loss. This study investigated whether elderly hearing-impaired (HI) listeners still achieve similar SRMs as young normal-hearing (NH) listeners, when SRMs are elicited by small ITDs.

Speech reception thresholds (SRTs) and SRM due to ITDs were measured over headphones for 10 young NH and 10 older HI listeners, who had normal or close-to-normal hearing below 1.5 kHz. Diotic target sentences were presented in diotic or dichotic speech-shaped noise or two-talker babble maskers. In the dichotic conditions, maskers were lateralized by delaying the masker waveforms in the left headphone channel.

Multiple magnitudes of masker ITDs were tested in both noise conditions. Although deficits were observed in speech perception abilities in speechshaped noise and two-talker babble in terms of SRTs, HI listeners could utilize ITDs to a similar degree as NH listeners to facilitate the binaural unmasking of speech.

A slight difference was observed between the group means when target and maskers were separated from each other by large ITDs, but not when separated by small ITDs. Thus, HI listeners do not appear to require larger ITDs than NH listeners do in order to receive a benefit from binaural unmasking.