The perception of consonants in reverberation and noise by adults fitted with bimodal devices

Purpose The purpose of this study was to evaluate the contribution of a contralateral hearing aid (HA) to the perception of consonants, in terms of voicing, manner, and place of articulation cues in reverberation and noise by adult cochlear implantees aided by bimodal fittings. Method Eight post-lingually deafened adult cochlear implant listeners with a fully inserted cochlear implant in one ear and low-frequency hearing in the other ear were tested on consonant perception. The subjects were presented with consonant stimuli processed in the following experimental conditions: one quiet condition, two different reverberation times (0.3 s and 1.0 s), and the combination of two reverberation times with a single signal-to-noise ratio (SNR = 5 dB). Results Consonant perception improved significantly when listening in combination with a contralateral hearing aid (HA) as opposed to listening with a cochlear implant (CI) alone in 0.3 s and 1.0 s of reverberation. Significantly higher scores were also noted when noise was added to 0.3 s of reverberation. Conclusion A considerable benefit was noted from the additional acoustic information in conditions of reverberation and reverberation plus noise. The bimodal benefit observed was more pronounced for voicing and manner of articulation than for place of articulation

Multi-microphone adaptive noise reduction strategies for coordinated stimulation in bilateral cochlear implant devices

This is the published version, also available here: http://dx.doi.org/10.1121/1.3372727.Bilateral cochlear implant (BI-CI) recipients achieve high word recognition scores in quiet listening conditions. Still, there is a substantial drop in speech recognition performance when there is reverberation and more than one interferers. BI-CI users utilize information from just two directional microphones placed on opposite sides of the head in a so-called independent stimulation mode. To enhance the ability of BI-CI users to communicate in noise, the use of two computationally inexpensive multi-microphone adaptive noise reduction strategies exploiting information simultaneously collected by the microphones associated with two behind-the-ear (BTE) processors (one per ear) is proposed. To this end, as many as four microphones are employed (two omni-directional and two directional) in each of the two BTE processors (one per ear). In the proposed two-microphone binaural strategies, all four microphones (two behind each ear) are being used in a coordinated stimulation mode. The hypothesis is that such strategies combine spatial information from all microphones to form a better representation of the target than that made available with only a single input. Speech intelligibility is assessed in BI-CI listeners using IEEE sentences corrupted by up to three steady speech-shaped noise sources. Results indicate that multi-microphone strategies improve speech understanding in single- and multi-noise source scenarios

Using blind source separation techniques to improve speech recognition in bilateral cochlear implant patients

This is the published version, also available here: http://dx.doi.org/10.1121/1.2839887.Bilateral cochlear implants seek to restore the advantages of binaural hearing by improving access to binaural cues. Bilateral implant users are currently fitted with two processors, one in each ear, operating independent of one another. In this work, a different approach to bilateral processing is explored based on blind source separation (BSS) by utilizing two implants driven by a single processor. Sentences corrupted by interfering speech or speech-shaped noise are presented to bilateral cochlear implant users at 0dB signal-to-noise ratio in order to evaluate the performance of the proposed BSS method. Subjects are tested in both anechoic and reverberant settings, wherein the target and masker signals are spatially separated. Results indicate substantial improvements in performance in both anechoic and reverberant settings over the subjects’ daily strategies for both masker conditions and at various locations of the masker. It is speculated that such improvements are due to the fact that the proposed BSS algorithm capitalizes on the variations of interaural level differences and interaural time delays present in the mixtures of the signals received by the two microphones, and exploits that information to spatially separate the target from the masker signals

Effects of early and late reflections on intelligibility of reverberated speech by cochlear implant listeners

This is the published version, also available here: http://dx.doi.org/10.1121/1.4834455.The purpose of this study was to determine the overall impact of early and late reflections on the intelligibility of reverberated speech by cochlear implant listeners. Two specific reverberation times were assessed. For each reverberation time, sentences were presented in three different conditions wherein the target signal was filtered through the early, late or entire part of the acoustic impulse response. Results obtained with seven cochlear implant listeners indicated that while early reflections neither enhanced nor reduced overall speech perception performance, late reflections severely reduced speech intelligibility in both reverberant conditions tested

A channel-selection criterion for suppressing reverberation in cochlear implants

This is the published version, also available here: http://dx.doi.org/10.1121/1.3559683.Little is known about the extent to which reverberation affects speech intelligibility by cochlear implant (CI) listeners. Experiment 1 assessed CI users’ performance using Institute of Electrical and Electronics Engineers (IEEE) sentences corrupted with varying degrees of reverberation. Reverberation times of 0.30, 0.60, 0.80, and 1.0 s were used. Results indicated that for all subjects tested, speech intelligibility decreased exponentially with an increase in reverberation time. A decaying-exponential model provided an excellent fit to the data. Experiment 2 evaluated (offline) a speech coding strategy for reverberation suppression using a channel-selection criterion based on the signal-to-reverberant ratio (SRR) of individual frequency channels. The SRR reflects implicitly the ratio of the energies of the signal originating from the early (and direct) reflections and the signal originating from the late reflections. Channels with SRR larger than a preset threshold were selected, while channels with SRR smaller than the threshold were zeroed out. Results in a highly reverberant scenario indicated that the proposed strategy led to substantial gains (over 60 percentage points) in speech intelligibility over the subjects’ daily strategy. Further analysis indicated that the proposed channel-selection criterion reduces the temporal envelope smearing effects introduced by reverberation and also diminishes the self-masking effects responsible for flattened formants

Spatially separating language masker from target results in spatial and linguistic masking release

Several studies demonstrate that in complex auditory scenes, speech recognition is improved when the competing background and target speech differ linguistically. However, such studies typically utilize spatially co-located speech sources which may not fully capture typical listening conditions. Furthermore, co-located presentation may overestimate the observed benefit of linguistic dissimilarity. The current study examines the effect of spatial separation on linguistic release from masking. Results demonstrate that linguistic release from masking does extend to spatially separated sources. The overall magnitude of the observed effect, however, appears to be diminished relative to the co-located presentation conditions

The impact of reverberant self-masking and overlap-masking effects on speech intelligibility by cochlear implant listeners (L)

This is the published version, also available here: http://dx.doi.org/10.1121/1.3614539.The purpose of this study is to determine the relative impact of reverberant self-masking and overlap-masking effects on speech intelligibility by cochlear implant listeners. Sentences were presented in two conditions wherein reverberant consonant segments were replaced with clean consonants, and in another condition wherein reverberant vowel segments were replaced with clean vowels. The underlying assumption is that self-masking effects would dominate in the first condition, whereas overlap-masking effects would dominate in the second condition. Results indicated that the degradation of speech intelligibility in reverberant conditions is caused primarily by self-masking effects that give rise to flattened formant transitions

Binaural advantages in users of bimodal and bilateral cochlear implant devices

This is the published version, also available here: http://dx.doi.org/10.1121/1.4831955.This paper investigates to what extent users of bilateral and bimodal fittings should expect to benefit from all three different binaural advantages found to be present in normal-hearing listeners. Head-shadow and binaural squelch are advantages occurring under spatially separated speech and noise, while summation emerges when speech and noise coincide in space. For 14 bilateral or bimodal listeners, speech reception thresholds in the presence of four-talker babble were measured in sound-field under various speech and noise configurations. Statistical analysis revealed significant advantages of head-shadow and summation for both bilateral and bimodal listeners. Squelch was significant only for bimodal listeners