Role of binaural hearing in speech intelligibility and spatial release from masking using vocoded speech

Abstract

A cochlear implant vocoder was used to evaluate relative contributions of spectral and binaural temporal fine-structure cues to speech intelligibility. In Study I, stimuli were vocoded, and then convolved through head related transfer functions ͑HRTFs͒ to remove speech temporal fine structure but preserve the binaural temporal fine-structure cues. In Study II, the order of processing was reversed to remove both speech and binaural temporal fine-structure cues. Speech reception thresholds ͑SRTs͒ were measured adaptively in quiet, and with interfering speech, for unprocessed and vocoded speech ͑16, 8, and 4 frequency bands͒, under binaural or monaural ͑right-ear͒ conditions. Under binaural conditions, as the number of bands decreased, SRTs increased. With decreasing number of frequency bands, greater benefit from spatial separation of target and interferer was observed, especially in the 8-band condition. The present results demonstrate a strong role of the binaural cues in spectrally degraded speech, when the target and interfering speech are more likely to be confused. The nearly normal binaural benefits under present simulation conditions and the lack of order of processing effect further suggest that preservation of binaural cues is likely to improve performance in bilaterally implanted recipients.

The influence of non-spatial factors on measures of spatial release from masking

“…However, their results are in the opposite direction to those reported here-they found that progressively coarser vocoding increased SRM in their task, which involved the identification of spondaic words against sentence maskers. This discrepancy between the two studies may reflect the fact that the targets used by Garadat et al (2009) were not confusable with the maskers, and thus task performance was not limited by IM. Consistent with this speculation, their listeners achieved extremely low thresholds even in the colocated configuration, with the group mean thresholds reported to be lower than À 20 dB TMR for unprocessed stimuli.…”

“…Thus, we strongly doubt that the measured SRM would be similar, as observed by Garadat et al (2009) and Drennan et al (2007) under their experimental conditions.…”

The effect of tone-vocoding on spatial release from masking for old, hearing-impaired listeners

“…The effect of noise vocoding on SRM was predominantly driven by the interaural correlation of the noise carriers below 1.5 kHz. On the other hand, Garadat et al (2009) conducted a similar study to Andersen et al (2010), but found that greater SRM was achieved with the TVC than without, and that there was no difference in performance between applying vocoding before or after HRIRs. However, Garadat et al (2009) only used a single masker sentence lateralized to one side, allowing the listeners to take advantage of the improved SNR at the other ear.…”

Development of Spatial Release From Masking in Mandarin-Speaking Children With Normal Hearing

“…To the best of our knowledge, the effect of energetic and informational masking has not been systematically investigated in the same group of children using repeated measures. In future developmental studies on SRM, the effect of the energeticinformational masking spectrum should be systematically investigated to reveal the maturation of bottom-up peripheral auditory processing versus top-down central auditory executive control through the use of different numbers of talker babbles or noise-excited vocoded speech with different numbers of bands (Garadat, Litovsky, Yu, & Zeng, 2009). It is anticipated that maskers with a higher degree of informational masking could reveal a longer developmental time for SNR-50% for NS and SRM measures, as it involves more top-down central auditory executive control at the cortical level that requires a longer developmental period to reach adult performance levels.…”