Effects of spectral resolution and smearing on gated word recognition

Abstract

In a word gating task, listeners are presented with increasing amounts of word-onset information (a series of increasingly longer temporal “gates”), and following each gate, they are asked to indicate what they think the target word is. Listeners with normal hearing (NH) typically recognize a target word well before they “hear” the entire word. Listeners with cochlear implants (CIs), however, need to hear almost the entire target word (require a greater amount of word-onset information) to recognize it. Here, we hypothesized that the poor spectral resolution, due to the limited number of channels and interactions between adjacent channels, may have a negative impact on gated word recognition performance. We manipulated spectral resolution by using: (1) a noise-band vocoder with a variable number of spectral channels; and (2) a vocoder with variable carrier filter slopes to simulate channel interaction. We determined the minimum amount of word-onset information required to recognize spoken words. Initial results suggest that the gated word recognition performance remained roughly unchanged as the amount of spectral degradation applied increased up to some extent, beyond which it deteriorated. With eight channels, which resemble the spectral resolution available to most CI users, even the most focused stimulation yielded poorer results.