Contribution of Temporal Fine Structure Cues to Concurrent Vowel Identification and Perception of Zebra Speech.

Introduction The limited access to temporal fine structure (TFS) cues is a reason for reduced speech-in-noise recognition in cochlear implant (CI) users. The CI signal processing schemes like electroacoustic stimulation (EAS) and fine structure processing (FSP) encode TFS in the low frequency whereas theoretical strategies such as frequency amplitude modulation encoder (FAME) encode TFS in all the bands. Objective The present study compared the effect of simulated CI signal processing schemes that either encode no TFS, TFS information in all bands, or TFS only in low-frequency bands on concurrent vowel identification (CVI) and Zebra speech perception (ZSP). Methods Temporal fine structure information was systematically manipulated using a 30-band sine-wave (SV) vocoder. The TFS was either absent (SV) or presented in all the bands as frequency modulations simulating the FAME algorithm or only in bands below 525 Hz to simulate EAS. Concurrent vowel identification and ZSP were measured under each condition in 15 adults with normal hearing. Results The CVI scores did not differ between the 3 schemes (F (2, 28) = 0.62, p = 0.55, η 2 p = 0.04). The effect of encoding TFS was observed for ZSP (F (2, 28) = 5.73, p = 0.008, η 2 p = 0.29). Perception of Zebra speech was significantly better with EAS and FAME than with SV. There was no significant difference in ZSP scores obtained with EAS and FAME ( p = 1.00) Conclusion For ZSP, the TFS cues from FAME and EAS resulted in equivalent improvements in performance compared to the SV scheme. The presence or absence of TFS did not affect the CVI scores.

Effect of inter-aural temporal envelope differences on inter-aural time difference thresholds for amplitude modulated noise.

PURPOSE: The inter-aural time difference (ITD) and inter-aural level difference (ILD) are important acoustic cues for horizontal localization and spatial release from masking. These cues are encoded based on inter-aural comparisons of tonotopically matched binaural inputs. Therefore, binaural coherence or the interaural spectro-temporal similarity is a pre-requisite for encoding ITD and ILD. The modulation depth of envelope is an important envelope characteristic that helps in encoding the envelope-ITD. However, inter-aural difference in modulation depth can result in reduced binaural coherence and poor representation of binaural cues as in the case with reverberation, noise and compression in cochlear implants and hearing aids. This study investigated the effect of inter-aural modulation depth difference on the ITD thresholds for an amplitude-modulated noise in normal hearing young adults. METHODS: An amplitude modulated high pass filtered noise with varying modulation depth differences was presented sequentially through headphones. In one ear, the modulation depth was retained at 90% and in the other ear it varied from 90% to 50%. The ITD thresholds for modulation frequencies of 8 Hz and 16 Hz were estimated as a function of the inter-aural modulation depth difference. RESULTS: The Friedman test findings revealed a statistically significant increase in the ITD threshold with an increase in the inter-aural modulation depth difference for 8 Hz and 16 Hz. CONCLUSION: The results indicate that the inter-aural differences in the modulation depth negatively impact ITD perception for an amplitude-modulated high pass filtered noise.

Effect of inter-aural temporal envelope differences on inter-aural time difference thresholds for amplitude modulated noise

ABSTRACT Purpose The inter-aural time difference (ITD) and inter-aural level difference (ILD) are important acoustic cues for horizontal localization and spatial release from masking. These cues are encoded based on inter-aural comparisons of tonotopically matched binaural inputs. Therefore, binaural coherence or the interaural spectro-temporal similarity is a pre-requisite for encoding ITD and ILD. The modulation depth of envelope is an important envelope characteristic that helps in encoding the envelope-ITD. However, inter-aural difference in modulation depth can result in reduced binaural coherence and poor representation of binaural cues as in the case with reverberation, noise and compression in cochlear implants and hearing aids. This study investigated the effect of inter-aural modulation depth difference on the ITD thresholds for an amplitude-modulated noise in normal hearing young adults. Methods An amplitude modulated high pass filtered noise with varying modulation depth differences was presented sequentially through headphones. In one ear, the modulation depth was retained at 90% and in the other ear it varied from 90% to 50%. The ITD thresholds for modulation frequencies of 8 Hz and 16 Hz were estimated as a function of the inter-aural modulation depth difference. Results The Friedman test findings revealed a statistically significant increase in the ITD threshold with an increase in the inter-aural modulation depth difference for 8 Hz and 16 Hz. Conclusion The results indicate that the inter-aural differences in the modulation depth negatively impact ITD perception for an amplitude-modulated high pass filtered noise.

Effect of interaural electrode insertion depth difference and independent band selection on sentence recognition in noise and spatial release from masking in simulated bilateral cochlear implant listening.

PURPOSE: Inter-aural insertion depth difference (IEDD) in bilateral cochlear implant (BiCI) with continuous interleaved sampling (CIS) processing is known to reduce the recognition of speech in noise and spatial release from masking (SRM). However, the independent channel selection in the 'n-of-m' sound coding strategy might have a different effect on speech recognition and SRM when compared to the effects of IEDD in CIS-based findings. This study aimed to investigate the effect of bilateral 'n-of-m' processing strategy and interaural electrode insertion depth difference on speech recognition in noise and SRM under conditions that simulated bilateral cochlear implant listening. METHODS: Five young adults with normal hearing sensitivity participated in the study. The target sentences were spatially filtered to originate from 0° and the masker was spatially filtered at 0°, 15°, 37.5°, and 90° using the Oldenburg head-related transfer function database for behind the ear microphone. A 22-channel sine wave vocoder processing based on 'n-of-m' processing was applied to the spatialized target-masker mixture, in each ear. The perceptual experiment involved a test of speech recognition in noise under one co-located condition (target and masker at 0°) and three spatially separated conditions (target at 0°, masker at 15°, 37.5°, or 90° to the right ear). RESULTS: The results were analyzed using a three-way repeated measure analysis of variance (ANOVA). The effect of interaural insertion depth difference (F (2,8) = 3.145, p = 0.098, ɳ2 = 0.007) and spatial separation between target and masker (F (3,12) = 1.239, p = 0.339, ɳ2 = 0.004) on speech recognition in noise was not significant. CONCLUSIONS: Speech recognition in noise and SRM were not affected by IEDD ≤ 3 mm. Bilateral 'n-of-m' processing resulted in reduced speech recognition in noise and SRM.

A system for spatial hearing research.

The spatial hearing experiments can be simulated using high-fidelity headphones. But these simulated experiments do not account for individual variations and are difficult to investigate when the listener is wearing hearing devices. Hence, the free-field systems are ideal for spatial hearing experiments. However, these systems are not readily available and must be customized based on experimental needs. This paper provides a brief overview of a spatial hearing research facility that is customized to perform experiments on individuals with normal hearing and hearing aid users. •This setup enables the assessment of spatial acuity with 10° precision in the horizontal plane.•The laboratory's universal design enables modifications based on experimental needs with minimum effort.•The signal processing and response acquisition systems are custom designed using MATLAB.