Spatial release from masking for noise-vocoded speech

Abstract

Spatially separating a speech target from interfering masker(s) generally improves target intelligibility; an effect known as spatial release from masking (SRM). This study assessed the contribution of envelope cues to SRM. Target speech was presented from the front (0° azimuth) and speech maskers were either colocated or symmetrically separated from the target in azimuth (±15°, ±30°, ±45° and ±90°) using KEMAR head-related transfer functions. The target and maskers were presented either as natural speech or as noise-vocoded speech. For the vocoded speech, intelligibility was conveyed only by the envelopes from M frequency bands. Experiment 1 examined the effects of varying the number of frequency bands for the vocoder, and the degree of target-masker spatial separation, on SRM. Experiment 2 examined the effects of low-pass filtering the envelopes of the vocoded speech bands on SRM. Preliminary results for Experiment 1 indicated that SRM improved as the number of spectral channels providing independent envelope cues increased for all spatial separations. Preliminary results for Experiment 2 showed no difference in SRM between low and high envelope-frequency cutoffs. Potential implications for studying hearing-impaired and cochlear-implant subjects will be discussed.