Mandarin speech perception in combined electric and acoustic stimulation.

For deaf individuals with residual low-frequency acoustic hearing, combined use of a cochlear implant (CI) and hearing aid (HA) typically provides better speech understanding than with either device alone. Because of coarse spectral resolution, CIs do not provide fundamental frequency (F0) information that contributes to understanding of tonal languages such as Mandarin Chinese. The HA can provide good representation of F0 and, depending on the range of aided acoustic hearing, first and second formant (F1 and F2) information. In this study, Mandarin tone, vowel, and consonant recognition in quiet and noise was measured in 12 adult Mandarin-speaking bimodal listeners with the CI-only and with the CI+HA. Tone recognition was significantly better with the CI+HA in noise, but not in quiet. Vowel recognition was significantly better with the CI+HA in quiet, but not in noise. There was no significant difference in consonant recognition between the CI-only and the CI+HA in quiet or in noise. There was a wide range in bimodal benefit, with improvements often greater than 20 percentage points in some tests and conditions. The bimodal benefit was compared to CI subjects' HA-aided pure-tone average (PTA) thresholds between 250 and 2000 Hz; subjects were divided into two groups: "better" PTA (<50 dB HL) or "poorer" PTA (>50 dB HL). The bimodal benefit differed significantly between groups only for consonant recognition. The bimodal benefit for tone recognition in quiet was significantly correlated with CI experience, suggesting that bimodal CI users learn to better combine low-frequency spectro-temporal information from acoustic hearing with temporal envelope information from electric hearing. Given the small number of subjects in this study (n = 12), further research with Chinese bimodal listeners may provide more information regarding the contribution of acoustic and electric hearing to tonal language perception

The perception of Cantonese lexical tones by early-deafened cochlear implantees

This study investigated whether cochlear implant users can identify Cantonese lexical tones, which differ primarily in their FO pattern. Seventeen early-deafened deaf children (age=4 years, 6 months to 8 years, 11 months; postoperative period = 11 - 41 months) took part in the study. Sixteen children were fitted with the Nucleus 24 cochlear implant system; one child was fitted with a Nucleus 22 implant. Participants completed a 2AFC picture identification task in which they identified one of the six contrastive Cantonese tones produced on the monosyllabic target word /ji/. Each target stimulus represented a concrete object and was presented within a carrier phrase in sentence-medial position. Group performance was significantly above chance for three contrasts. However, the cochlear implant listeners performed much worse than a 6 1/2-year-old, moderately hearing impaired control listener who was tested on the same task. These findings suggest that this group of cochlear implant users had great difficulty in extracting the pitch information needed to accurately identify Cantonese lexical tones. © 2002 Acoustical Society of America.published_or_final_versio

Improving the Speech Intelligibility By Cochlear Implant Users

In this thesis, we focus on improving the intelligibility of speech for cochlear implants (CI) users. As an auditory prosthetic device, CI can restore hearing sensations for most patients with profound hearing loss in both ears in a quiet background. However, CI users still have serious problems in understanding speech in noisy and reverberant environments. Also, bandwidth limitation, missing temporal fine structures, and reduced spectral resolution due to a limited number of electrodes are other factors that raise the difficulty of hearing in noisy conditions for CI users, regardless of the type of noise. To mitigate these difficulties for CI listener, we investigate several contributing factors such as the effects of low harmonics on tone identification in natural and vocoded speech, the contribution of matched envelope dynamic range to the binaural benefits and contribution of low-frequency harmonics to tone identification in quiet and six-talker babble background. These results revealed several promising methods for improving speech intelligibility for CI patients. In addition, we investigate the benefits of voice conversion in improving speech intelligibility for CI users, which was motivated by an earlier study showing that familiarity with a talker’s voice can improve understanding of the conversation. Research has shown that when adults are familiar with someone’s voice, they can more accurately – and even more quickly – process and understand what the person is saying. This theory identified as the “familiar talker advantage” was our motivation to examine its effect on CI patients using voice conversion technique. In the present research, we propose a new method based on multi-channel voice conversion to improve the intelligibility of transformed speeches for CI patients

Design and evaluation of tone-enhanced strategy for cochlear implants in noisy environment.

Yu, Shing.Thesis (M.Phil.)--Chinese University of Hong Kong, 2011.Includes bibliographical references (leaves 87-93).Abstracts in English and Chinese; includes Chinese.Abstract --- p.iAcknowledgement --- p.viChapter 1 --- Introduction --- p.1Chapter 1.1 --- Hearing impairment --- p.1Chapter 1.2 --- Limitations of existing CI --- p.2Chapter 1.3 --- Objectives --- p.3Chapter 1.4 --- Thesis Outline --- p.4Chapter 2 --- Background --- p.6Chapter 2.1 --- Signal Processing in CI --- p.6Chapter 2.1.1 --- Continuous Interleaved Sampler (CIS) --- p.7Chapter 2.1.2 --- Advanced Combination Encoder (ACE) --- p.12Chapter 2.2 --- Tone perception by cochlear implantees --- p.15Chapter 2.2.1 --- Pitch and Tone --- p.15Chapter 2.2.2 --- Mechanisms of pitch perception by cochlear im- plantees --- p.20Chapter 3 --- Tone-enhanced ACE Strategy for CI --- p.23Chapter 3.1 --- Basic principles --- p.23Chapter 3.2 --- Acoustical simulation with noise excited vocoder --- p.26Chapter 3.3 --- Implementation in a real CI system --- p.29Chapter 3.3.1 --- Technical details --- p.30Chapter 3.3.2 --- Visual comparison --- p.31Chapter 4 --- Robust Generation of F0 Trajectory --- p.33Chapter 4.1 --- Requirement on the F0 contour --- p.33Chapter 4.2 --- Extraction of F0 contour --- p.34Chapter 4.3 --- Post-processing of F0 contour --- p.36Chapter 4.3.1 --- Removal of octave-jump --- p.36Chapter 4.3.2 --- Interpolation --- p.36Chapter 4.3.3 --- Prediction --- p.36Chapter 4.3.4 --- Smoothing --- p.38Chapter 4.4 --- Performance evaluation --- p.38Chapter 5 --- Design of Listening Tests --- p.41Chapter 5.1 --- Speech Materials --- p.41Chapter 5.2 --- Testing modes --- p.43Chapter 5.2.1 --- Sound field mode --- p.45Chapter 5.2.2 --- Direct stimulation mode --- p.46Chapter 5.3 --- Test Interface --- p.47Chapter 6 --- Sound-field Tests --- p.49Chapter 6.1 --- Materials and Methods --- p.50Chapter 6.1.1 --- Subjects --- p.50Chapter 6.1.2 --- Signal processing and test stimuli --- p.52Chapter 6.1.3 --- Procedures --- p.52Chapter 6.2 --- Results --- p.54Chapter 6.3 --- Discussion --- p.57Chapter 7 --- Evaluation of Tone-enhanced Strategy --- p.59Chapter 7.1 --- Materials and Methods --- p.60Chapter 7.1.1 --- Subjects --- p.60Chapter 7.1.2 --- Signal processing and test stimuli --- p.60Chapter 7.1.3 --- Procedures --- p.62Chapter 7.2 --- Results --- p.63Chapter 7.3 --- Discussion --- p.66Chapter 8 --- Use of Automatically Generated F0 Contour --- p.72Chapter 8.1 --- Materials and Methods --- p.73Chapter 8.2 --- Results --- p.74Chapter 8.3 --- Discussion --- p.76Chapter 9 --- Conclusions --- p.80Chapter A --- LSHK Cantonese Romanization Scheme --- p.85Bibliography --- p.8

The Human Auditory System

This book presents the latest findings in clinical audiology with a strong emphasis on new emerging technologies that facilitate and optimize a better assessment of the patient. The book has been edited with a strong educational perspective (all chapters include an introduction to their corresponding topic and a glossary of terms). The book contains material suitable for graduate students in audiology, ENT, hearing science and neuroscience

On the mechanism of response latencies in auditory nerve fibers

Despite the structural differences of the middle and inner ears, the latency pattern in auditory nerve fibers to an identical sound has been found similar across numerous species. Studies have shown the similarity in remarkable species with distinct cochleae or even without a basilar membrane. This stimulus-, neuron-, and species- independent similarity of latency cannot be simply explained by the concept of cochlear traveling waves that is generally accepted as the main cause of the neural latency pattern. An original concept of Fourier pattern is defined, intended to characterize a feature of temporal processing—specifically phase encoding—that is not readily apparent in more conventional analyses. The pattern is created by marking the first amplitude maximum for each sinusoid component of the stimulus, to encode phase information. The hypothesis is that the hearing organ serves as a running analyzer whose output reflects synchronization of auditory neural activity consistent with the Fourier pattern. A combined research of experimental, correlational and meta-analysis approaches is used to test the hypothesis. Manipulations included phase encoding and stimuli to test their effects on the predicted latency pattern. Animal studies in the literature using the same stimulus were then compared to determine the degree of relationship. The results show that each marking accounts for a large percentage of a corresponding peak latency in the peristimulus-time histogram. For each of the stimuli considered, the latency predicted by the Fourier pattern is highly correlated with the observed latency in the auditory nerve fiber of representative species. The results suggest that the hearing organ analyzes not only amplitude spectrum but also phase information in Fourier analysis, to distribute the specific spikes among auditory nerve fibers and within a single unit. This phase-encoding mechanism in Fourier analysis is proposed to be the common mechanism that, in the face of species differences in peripheral auditory hardware, accounts for the considerable similarities across species in their latency-by-frequency functions, in turn assuring optimal phase encoding across species. Also, the mechanism has the potential to improve phase encoding of cochlear implants

The perception and production of stress and intonation by children with cochlear implants

Users of current cochlear implants have limited access to pitch information and hence to intonation in speech. This seems likely to have an important impact on prosodic perception. This thesis examines the perception and production of the prosody of stress in children with cochlear implants. The interdependence of perceptual cues to stress (pitch, timing and loudness) in English is well documented and each of these is considered in analyses of both perception and production. The subject group comprised 17 implanted (CI) children aged 5;7 to 16;11 and using ACE or SPEAK processing strategies. The aims are to establish (i) the extent to which stress and intonation are conveyed to CI children in synthesised bisyllables (BAba vs. baBA) involving controlled changes in F0, duration and amplitude (Experiment I), and in natural speech involving compound vs. phrase stress and focus (Experiment II). (ii) when pitch cues are missing or are inaudible to the listeners, do other cues such as loudness or timing contribute to the perception of stress and intonation? (iii) whether CI subjects make appropriate use of F0, duration and amplitude to convey linguistic focus in speech production (Experiment III). Results of Experiment I showed that seven of the subjects were unable to reliably hear pitch differences of 0.84 octaves. Most of the remaining subjects required a large (approx 0.5 octave) difference to reliably hear a pitch change. Performance of the CI children was poorer than that of a normal hearing group of children presented with an acoustic cochlear implant simulation. Some of the CI children who could not discriminate F0 differences in Experiment I nevertheless scored above chance in tests involving focus in natural speech in Experiment II. Similarly, some CI subjects who were above chance in the production of appropriate F0 contours in Experiment III could not hear F0 differences of 0.84 octaves. These results suggest that CI children may not necessarily rely on F0 cues to stress, and in the absence of F0 or amplitude cues, duration may provide an alternative cue