The effect of interaural differences of time on speech intelligibility in simulated electric-acoustic hearing

Abstract

Individuals with residual hearing restricted to frequencies below about 500–750 Hz have recently been implanted with a relatively short electrode array designed to preserve as much of the residual hearing as possible. Those who also have some low-frequency hearing in the non-implanted ear have the potential to benefit from interaural time differences (ITD). The goal of the current experiments was to determine whether such benefit exists in simulations of implant listening and how it is influenced by sensation level (SL) in the low frequencies. Presentation was via headphones. Target and distractor speech were low-pass filtered at 500 Hz. The target was presented diotically and the distractor was presented with a 0-s (spatially centered image) or 600-s (image to the right) ITD. The target and distractor were also processed by a four-channel vocoder and presented to the left ear only. The SL of the low-frequency speech was varied both symmetrically and asymmetrically. In the symmetric conditions (15–60 dB SL), intelligibility improved by as much as 40% when the target and distractor were spatially separated. In the asymmetric conditions (60 dB in one ear, 20–50 dB in the other), approximately 15%–20% improvement was observed in all conditions. [Work supported by NIH and NOHR.]