Dichotic speech recognition in noise using reduced spectral cues

It is generally accepted that the fusion of two speech signals presented dichotically is affected by the relative onset time. This study investigated the hypothesis that spectral resolution might be an additional factor influencing spectral fusion when the spectral information is split and presented dichotically to the two ears. To produce speech with varying degrees of spectral resolution, speech materials embedded in +5 dB S/N speech-shaped noise were processed through 6-12 channels and synthesized as a sum of sine waves. Two different methods of splitting the spectral information were investigated. In the first method, the odd-index channels were presented to one ear and the even-index channels to the other ear. In the second method the lower frequency channels were presented to one ear and the high-frequency channels to the other ear. Results indicated that spectral resolution did affect spectral fusion, and the effect differed across speech materials, with the sentences being affected the most. Sentences, processed through six or eight channels and presented dichotically in the low-high frequency condition were not fused as accurately as when presented monaurally. Sentences presented dichotically in the odd-even frequency condition were identified more accurately than when presented in the low-high condition.