Learning to discriminate reduced-channel /bɑ/–/wɑ/ syllables in normal-hearing adults

Abstract

Acoustic information delivered to individuals with cochlear implants differs in many ways from the same information delivered via a normally functioning cochlea. One difference is that the number of frequencies that can be distinguished is sharply reduced in implanted listeners. This results in poor frequency selectivity where only sounds that fall into different frequency bands are distinguishable (all other things being equal). Shannon [Science 270, 303–304 (1995)] used an electrical filtering and rectification system to simulate this aspect of cochlear implant function in normal-hearing listeners. In the present study software filtering was combined with envelope-shaped-noise (ESN) processing to accomplish the same end. The immediate goal was to examine the efficacy of a simple technique in training listeners to distinguish between reduced-channel versions of syllables. The stimuli tested were synthetically produced /bɑ/ and /wɑ/ syllables, identical in every aspect except for their onset duration. These syllables were filtered into eight frequency bands and ESN processed. Following this they were once-again filtered at the same frequencies to create reduced-channel versions of the original syllables. The resulting stimuli were presented to 16 normal-hearing adult subjects in behavioral and electrophysiological tasks. Results demonstrated that the training rapidly improved listeners’ abilities to identify reduced-channel /bɑ/ and /wɑ/.