The Production of Question Intonation by Young Adult Cochlear Implant Users: Does Age at Implantation Matter?

Purpose The purpose of this observational study was to investigate the properties of sentence-final prosody in yes/no questions produced by cochlear implant (CI) users in order to determine whether and how the age at CI implantation impacts CI users' production of question intonation later in life. Method We acoustically analyzed recordings from 46 young adult CI users and 10 young adults with normal hearing who read yes/no questions. Of the 46 CI users, 20 had received their CI before the age of 4.0 years (early implantation group), 15 between ages 4.0 and 8.11 years (midimplantation group), and 11 at the age of 9.0 years or later (late implantation group). We assessed the prosodic properties of the produced questions for each implantation group and the normal hearing comparison group (a) by measuring the sentence-final rise in fundamental frequency, (b) by labeling the question-final intonation contour using the Tones and Breaks Index ( Beckman & Ayers, 1994 ; Silverman, Beckman, et al., 1992 ; Veilleux, Shattuck-Hufnagel, & Brugos, 2006 ), and (c) by assessing phrase-final lengthening. Results The fundamental frequency rises produced by all CI users exhibited a smaller magnitude than those produced by the normal hearing comparison group, although the difference between early implanted CI users and the normal hearing group did not reach statistical significance. Early implanted CI users were more comparable in their use of question-final intonation contours to the individuals with typical hearing than to those users with CI implanted later in life. All CI users exhibited significantly less phrase-final lengthening than the normal hearing comparison group, regardless of age at CI implantation. Conclusion The results of this investigation of question intonation produced by CI users suggest that those CI users who were implanted with CI earlier in life produce yes/no question intonation in a manner that is more similar to, albeit not the same as, individuals with normal hearing when compared to the productions of those users with CI implanted after 4.0 years of age.

How Well Can Anaesthetists Discriminate Pulse Oximeter Tones?

The ability of experienced anaesthetists to discern oxygen saturation by listening to the tones of a Datex AS3 pulse oximeter was examined. Five-second samples were recorded using a high fidelity patient simulator and replayed singly and in pairs. Whilst the lower saturations were generally recognized as lower, the perceived range was greatly compressed. Median perceived estimates for 70% saturation was 89%, for 80% was 93% and for 94% was 94%. When comparing pairs of samples, the direction of the difference was correctly discerned by 70% of anaesthetists for differences of 2%, rising to 95% for differences of greater than 8% oxygen saturation. The magnitude of the difference was consistently underestimated. With an actual difference of 20%, the median estimate was 5%. The results indicate that while qualitative estimate changes in oxygen saturation are moderately reliable, quantitative estimation is severely limited by a compromised perceived scale. This may lead to underestimation of the severity if the auditory signal is relied on in isolation. A non-linear (musical) scale may prove more appropriate and should be investigated. Testing experienced anaesthetists demonstrated that most could detect the direction, but not the magnitude of a change in saturation by listening to the change in pitch of a Datex AS3 pulse oximeter tone.

Cortical thickness of Broca's area and right homologue is related to grammar learning aptitude and pitch discrimination proficiency

Aptitude for and proficiency in acquiring new languages varies in the human population but their neural bases are largely unknown. We investigated the influence of cortical thickness on language learning predictors measured by the LLAMA tests and a pitch-change discrimination test. The LLAMA tests are first language-independent assessments of language learning aptitude for vocabulary, phonetic working memory, sound-symbol correspondence (not used in this study), and grammatical inferencing. Pitch perception proficiency is known to predict aptitude for learning new phonology. Results show a correlation between scores in a grammatical meaning-inferencing aptitude test and cortical thickness of Broca's area (r(30) = 0.65, p = 0.0202) and other frontal areas (r(30) = 0.66, p = 0.0137). Further, a correlation was found between proficiency in discriminating pitch-change direction and cortical thickness of the right Broca homologue (r(30) = 0.57, p = 0.0006). However, no correlations were found for aptitude for vocabulary learning or phonetic working memory. Results contribute to locating cortical regions important for language-learning aptitude.

Automatic intonation classification using temporal patterns in utterance-level pitch contour and perceptually motivated pitch transformation

Second language learners of British English (BE) are typically trained for four intonation classes: Glide-up, Glide-down, Dive, and Take-off. Automatic four-way intonation classification could be useful to evaluate a learner's pronunciation. However, such automatic classification is challenging without having manually annotated tones, typically considered in intonation analysis and classification tasks. In this, a three-dimensional feature sequence is proposed representing temporal patterns in the utterance-level f0 contour using a perceptually motivated pitch transformation. Hidden Markov model based classification experiments conducted using a training material for teaching BE intonation demonstrate the benefit of the proposed approach over the baseline scheme considered.

Effects of the relative timing of opposite-polarity pulses on loudness for cochlear implant listeners

The symmetric biphasic pulses used in contemporary cochlear implants (CIs) consist of both cathodic and anodic currents, which may stimulate different sites on spiral ganglion neurons and, potentially, interact with each other. The effect on the order of anodic and cathodic stimulation on loudness at short inter-pulse intervals (IPIs; 0-800 μs) is investigated. Pairs of opposite-polarity pseudomonophasic (PS) pulses were used and the amplitude of each pulse was manipulated independently. In experiment 1 the two PS pulses differed in their current level in order to elicit the same loudness when presented separately. Six users of the Advanced Bionics CI (Valencia, CA) loudness-ranked trains of the pulse pairs using a midpoint-comparison procedure. Stimuli with anodic-leading polarity were louder than those with cathodic-leading polarity for IPIs shorter than 400 μs. This effect was small-about 0.3 dB-but consistent across listeners. When the same procedure was repeated with both PS pulses having the same current level (experiment 2), anodic-leading stimuli were still louder than cathodic-leading stimuli at very short intervals. However, when using symmetric biphasic pulses (experiment 3) the effect disappeared at short intervals and reversed at long intervals. Possible peripheral sources of such polarity interactions are discussed.

Fundamental-frequency discrimination based on temporal-envelope cues: Effects of bandwidth and interference

Both music and speech perception rely on hearing out one pitch in the presence of others. Pitch discrimination of narrowband sounds based only on temporal-envelope cues is rendered nearly impossible by introducing interferers in both normal-hearing listeners and cochlear-implant (CI) users. This study tested whether performance improves in normal-hearing listeners if the target is presented over a broad spectral region. The results indicate that performance is still strongly affected by spectrally remote interferers, despite increases in bandwidth, suggesting that envelope-based pitch is unlikely to allow CI users to perceive pitch when multiple harmonic sounds are presented at once.

Learning for pitch and melody discrimination in congenital amusia

Congenital amusia is currently thought to be a life-long neurogenetic disorder in music perception, impervious to training in pitch or melody discrimination. This study provides an explicit test of whether amusic deficits can be reduced with training. Twenty amusics and 20 matched controls participated in four sessions of psychophysical training involving either pure-tone (500 Hz) pitch discrimination or a control task of lateralization (interaural level differences for bandpass white noise). Pure-tone pitch discrimination at low, medium, and high frequencies (500, 2000, and 8000 Hz) was measured before and after training (pretest and posttest) to determine the specificity of learning. Melody discrimination was also assessed before and after training using the full Montreal Battery of Evaluation of Amusia, the most widely used standardized test to diagnose amusia. Amusics performed more poorly than controls in pitch but not localization discrimination, but both groups improved with practice on the trained stimuli. Learning was broad, occurring across all three frequencies and melody discrimination for all groups, including those who trained on the non-pitch control task. Following training, 11 of 20 amusics no longer met the global diagnostic criteria for amusia. A separate group of untrained controls (n = 20), who also completed melody discrimination and pretest, improved by an equal amount as trained controls on all measures, suggesting that the bulk of learning for the control group occurred very rapidly from the pretest. Thirty-one trained participants (13 amusics) returned one year later to assess long-term maintenance of pitch and melody discrimination. On average, there was no change in performance between posttest and one-year follow-up, demonstrating that improvements on pitch- and melody-related tasks in amusics and controls can be maintained. The findings indicate that amusia is not always a life-long deficit when using the current standard diagnostic criteria.

Mismatch negativity reflects asymmetric pre-attentive harmonic interval discrimination

Objective

Western music is based on intervals; thus, interval discrimination is important for distinguishing the character of melodies or tracking melodies in polyphonic music. In this study the encoding of intervals in simultaneously presented sound is studied.

Study design

In an electrophysiological experiment in 15 normal-hearing non-musicians, major thirds or fifths were presented in a controlled oddball paradigm. Harmonic intervals were created by simultaneously presented sinusoidals with randomized root frequency. Mismatch negativity (MMN) responses were measured with an EEG recording. The discrimination index was calculated in a psychoacoustic experiment.

Results

A clear MMN response was found for the major third but not for the fifth. The neural generators were located within the auditory cortices. Psychoacoustically, no evidence was found that the subjects were able to detect the deviants.

Conclusions

We conclude that pre-attentive discrimination of harmonic interval size is, in principle, possible in listeners without musical training although simultaneous presentation makes it harder to distinguish compared to non-overlapping intervals. Furthermore we see a difference in the response to infrequent dissonant stimuli in consonant standard stimuli compared to the opposite, rare consonant stimuli in dissonant standard stimuli.

The discrimination of voice cues in simulations of bimodal electro-acoustic cochlear-implant hearing

In discriminating speakers' voices, normal-hearing individuals effectively use two vocal characteristics, vocal pitch (related to fundamental frequency, F0) and vocal-tract length (VTL, related to speaker size). Typical cochlear-implant users show poor perception of these cues. However, in implant users with low-frequency residual acoustic hearing, this bimodal electro-acoustic stimulation may provide additional voice-related cues, such as low-numbered harmonics and formants, which could improve F0/VTL perception. In acoustic noise-vocoder simulations, where added low-pass filtered speech simulated residual hearing, a strong bimodal benefit was observed for F0 perception. No bimodal benefit was observed for VTL, which seems to mainly rely on vocoder spectral resolution.

Spectral Ripple Discrimination in Normal-Hearing Infants

OBJECTIVES

Spectral resolution is a correlate of open-set speech understanding in postlingually deaf adults and prelingually deaf children who use cochlear implants (CIs). To apply measures of spectral resolution to assess device efficacy in younger CI users, it is necessary to understand how spectral resolution develops in normal-hearing children. In this study, spectral ripple discrimination (SRD) was used to measure listeners' sensitivity to a shift in phase of the spectral envelope of a broadband noise. Both resolution of peak to peak location (frequency resolution) and peak to trough intensity (across-channel intensity resolution) are required for SRD.

DESIGN

SRD was measured as the highest ripple density (in ripples per octave) for which a listener could discriminate a 90° shift in phase of the sinusoidally-modulated amplitude spectrum. A 2 × 3 between-subjects design was used to assess the effects of age (7-month-old infants versus adults) and ripple peak/trough "depth" (10, 13, and 20 dB) on SRD in normal-hearing listeners (experiment 1). In experiment 2, SRD thresholds in the same age groups were compared using a task in which ripple starting phases were randomized across trials to obscure within-channel intensity cues. In experiment 3, the randomized starting phase method was used to measure SRD as a function of age (3-month-old infants, 7-month-old infants, and young adults) and ripple depth (10 and 20 dB in repeated measures design).

RESULTS

In experiment 1, there was a significant interaction between age and ripple depth. The infant SRDs were significantly poorer than the adult SRDs at 10 and 13 dB ripple depths but adult-like at 20 dB depth. This result is consistent with immature across-channel intensity resolution. In contrast, the trajectory of SRD as a function of depth was steeper for infants than adults suggesting that frequency resolution was better in infants than adults. However, in experiment 2 infant performance was significantly poorer than adults at 20 dB depth suggesting that variability of infants' use of within-channel intensity cues, rather than better frequency resolution, explained the results of experiment 1. In experiment 3, age effects were seen with both groups of infants showing poorer SRD than adults but, unlike experiment 1, no significant interaction between age and depth was seen.

CONCLUSIONS

Measurement of SRD thresholds in individual 3 to 7-month-old infants is feasible. Performance of normal-hearing infants on SRD may be limited by across-channel intensity resolution despite mature frequency resolution. These findings have significant implications for design and stimulus choice for applying SRD for testing infants with CIs. The high degree of variability in infant SRD can be somewhat reduced by obscuring within-channel cues.

Sensorimotor adaptation of voice fundamental frequency in Parkinson's disease

OBJECTIVE

This study examined adaptive responses to auditory perturbation of fundamental frequency (fo) in speakers with Parkinson's disease (PD) and control speakers.

METHOD

Sixteen speakers with PD and nineteen control speakers produced sustained vowels while they received perturbed auditory feedback (i.e., fo shifted upward or downward). Speakers' pitch acuity was quantified using a just-noticeable-difference (JND) paradigm. Twelve listeners provided estimates of the speech intelligibility for speakers with PD.

RESULTS

Fifteen responses from each speaker group for each shift direction were included in analyses. While control speakers generally showed consistent adaptive responses opposing the perturbation, speakers with PD showed no compensation on average, with individual PD speakers showing highly variable responses. In the PD group, the degree of compensation was not significantly correlated with age, disease progression, pitch acuity, or intelligibility.

CONCLUSIONS

These findings indicate reduced adaptation to sustained fo perturbation and higher variability in PD compared to control participants. No significant differences were seen in pitch acuity between groups, suggesting that the fo adaptation deficit in PD is not the result of purely perceptual mechanisms.

SIGNIFICANCE

These results suggest there is an impairment in vocal motor control in PD. Building on these results, contributions can be made to developing targeted voice treatments for PD.

Short Article: Knowing When to Hear Aids What to Hear

Temporal preparation often has been assumed to influence motor stages of information processing. Recent studies, however, challenge this notion and provide evidence for a facilitation of visual processing. The present study was designed to investigate whether perceptual processing in the auditory domain also benefits from temporal preparation. To this end, we employed a pitch discrimination task. In Experiment 1, discrimination performance was clearly improved when participants were temporally prepared. This finding was confirmed in Experiment 2, which ruled out possible influences of short-term memory. The results support the notion that temporal preparation enhances perceptual processing not only in the visual, but also in the auditory, modality.

Self-Selection of Frequency Tables with Bilateral Mismatches in an Acoustic Simulation of a Cochlear Implant

BACKGROUND

Many recipients of bilateral cochlear implants (CIs) may have differences in electrode insertion depth. Previous reports indicate that when a bilateral mismatch is imposed, performance on tests of speech understanding or sound localization becomes worse. If recipients of bilateral CIs cannot adjust to a difference in insertion depth, adjustments to the frequency table may be necessary to maximize bilateral performance.

PURPOSE

The purpose of this study was to examine the feasibility of using real-time manipulations of the frequency table to offset any decrements in performance resulting from a bilateral mismatch.

RESEARCH DESIGN

A simulation of a CI was used because it allows for explicit control of the size of a bilateral mismatch. Such control is not available with users of CIs.

STUDY SAMPLE

A total of 31 normal-hearing young adults participated in this study.

DATA COLLECTION AND ANALYSIS

Using a CI simulation, four bilateral mismatch conditions (0, 0.75, 1.5, and 3 mm) were created. In the left ear, the analysis filters and noise bands of the CI simulation were the same. In the right ear, the noise bands were shifted higher in frequency to simulate a bilateral mismatch. Then, listeners selected a frequency table in the right ear that was perceived as maximizing bilateral speech intelligibility. Word-recognition scores were then assessed for each bilateral mismatch condition. Listeners were tested with both a standard frequency table, which preserved a bilateral mismatch, or with their self-selected frequency table.

RESULTS

Consistent with previous reports, bilateral mismatches of 1.5 and 3 mm yielded decrements in word recognition when the standard table was used in both ears. However, when listeners used the self-selected frequency table, performance was the same regardless of the size of the bilateral mismatch.

CONCLUSIONS

Self-selection of a frequency table appears to be a feasible method for ameliorating the negative effects of a bilateral mismatch. These data may have implications for recipients of bilateral CIs who cannot adapt to a bilateral mismatch, because they suggest that (1) such individuals may benefit from modification of the frequency table in one ear and (2) self-selection of a "most intelligible" frequency table may be a useful tool for determining how the frequency table should be altered to optimize speech recognition.

Haptics in Music: The Effects of Vibrotactile Stimulus in Low Frequency Auditory Difference Detection Tasks

We present an experiment that investigated the effect of vibrotactile stimulation in auditory pitch discrimination tasks. Extra-auditory information was expected to have some influence upon the frequency discrimination of auditory Just Noticeable Difference (JND) detection levels at 160 Hz. To measure this, the potential to correctly identified positive and negative frequency changes for two randomly divided groups was measured and then compared. The first group was given an audio only JND test and the second group was given the same test, but with additional vibrotactile stimulus delivered via a vibrating glove device. The results of the experiment suggest that in musical interactions involving the selection of specific pitches, or the detection of pitch variation, vibrotactile feedback may have some advantageous effect upon a musician's ability to perceive changes when presented in synchrony with auditory stimulus.

Encoding a Melody Using Only Temporal Information for Cochlear-Implant and Normal-Hearing Listeners

One way to provide pitch information to cochlear implant users is through amplitude-modulation rate. It is currently unknown whether amplitude-modulation rate can provide cochlear implant users with pitch information adequate for perceiving melodic information. In the present study, the notes of a song were encoded via amplitude-modulation rate of pulse trains on single electrodes at the apex or middle of long electrode arrays. The melody of the song was either physically correct or modified by compression or expansion. Nine cochlear implant users rated the extent to which the song was out of tune in the different conditions. Cochlear implant users on average did not show sensitivity to melody compression or expansion regardless of place of stimulation. These results were found despite the fact that three of the cochlear implant users showed the expected sensitivity to melody compression and expansion with the same task using acoustic pure tones in a contralateral acoustic ear. Normal-hearing listeners showed an inconsistent and weak effect of melody compression and expansion when the notes of the song were encoded with acoustic pulse rate. The results suggest that amplitude-modulation rate provides insufficient access to melodic information for cochlear-implant and normal-hearing listeners.

Relating approach-to-target and detection tasks in animal psychoacoustics

Psychophysical experiments seek to measure the limits of perception. While straightforward in humans, in animals they are time consuming. Choosing an appropriate task and interpreting measurements can be challenging. We investigated the localization of high-frequency auditory signals in noise using an "approach-to-target" task in ferrets, how task performance should be interpreted in terms of perception, and how the measurements relate to other types of tasks. To establish their general ability to localize, animals were first trained to discriminate broadband noise from 12 locations. Subsequently we tested their ability to discriminate between band-limited targets at 2 or 3 more widely spaced locations, in a continuous background noise. The ability to discriminate between 3 possible locations (-90°, 0°, 90°) of a 10-kHz pure tone decreased gradually over a wide range (>30 dB) of signal-to-noise ratios (SNRs). Location discrimination ability was better for wide band noise targets (0.5 and 2 octave). These results were consistent with localization ability limiting performance for pure tones. Discrimination of pure tones at 2 locations (-90/left, 90/right) was robust at positive SNRs, yielding psychometric functions which fell steeply at negative SNRs. Thresholds for discrimination were similar to previous tone-in-noise thresholds measured in ferrets using a yes/no task. Thus, using an approach-to-target task, sound "localization" in noise can reflect detectability or the ability to localize, depending on the stimulus configuration. Signal-detection-theory-based models were able to account for the results when discriminating between pure tones from 2- and 3-source locations. (PsycINFO Database Record

Adaptation of Central Pitch-Specific Mechanisms

Three previous psychophysical studies have demonstrated that interaural time difference (ITD) coding mechanisms can undergo frequency-specific, selective adaptation. We sought to determine whether this phenomenon extends to the pitch domain, by employing the same psychophysical paradigm as one used previously, but with harmonic tone complexes lacking energy at the fundamental frequency. Ten normal listeners participated in experiment 1. Psychometric functions for ITDs were obtained for harmonic tone complexes with fundamental frequencies of 110 Hz and 185 Hz, before and after selective adaptation with complexes of the same fundamental frequencies lateralised to opposite sides. In experiment 1, each subject was tested twice. On separate days, subjects were tested with 110 Hz and 185 Hz stimuli that were either partially resolvable complexes or unresolvable ones. Both partially resolved and unresolved stimuli supported adaptation, and at both fundamental frequencies. In experiment 2, which employed nine listeners, the adaptor tone complexes were presented in conjunction with a diotic noise background designed to mask difference tones generated by the adaptor stimuli. The use of the masker had little effect on the mean strength of the adaptation effected by the unresolved adaptor stimuli, and only slightly weakened the adaptation effect found with the partially resolved adaptor stimuli. Taken together, these data constitute the first demonstration of selective adaptation exerted on a central mechanism in the pitch domain.

Pitch Processing in Tonal-Language-Speaking Children with Autism: An Event-Related Potential Study

The present study investigated pitch processing in Mandarin-speaking children with autism using event-related potential measures. Two experiments were designed to test how acoustic, phonetic and semantic properties of the stimuli contributed to the neural responses for pitch change detection and involuntary attentional orienting. In comparison with age-matched (6-12 years) typically developing controls (16 participants in Experiment 1, 18 in Experiment 2), children with autism (18 participants in Experiment 1, 16 in Experiment 2) showed enhanced neural discriminatory sensitivity in the nonspeech conditions but not for speech stimuli. The results indicate domain specificity of enhanced pitch processing in autism, which may interfere with lexical tone acquisition and language development for children who speak a tonal language.

Activation in the Right Inferior Parietal Lobule Reflects the Representation of Musical Structure beyond Simple Pitch Discrimination

Pitch discrimination tasks typically engage the superior temporal gyrus and the right inferior frontal gyrus. It is currently unclear whether these regions are equally involved in the processing of incongruous notes in melodies, which requires the representation of musical structure (tonality) in addition to pitch discrimination. To this aim, 14 participants completed two tasks while undergoing functional magnetic resonance imaging, one in which they had to identify a pitch change in a series of non-melodic repeating tones and a second in which they had to identify an incongruous note in a tonal melody. In both tasks, the deviants activated the right superior temporal gyrus. A contrast between deviants in the melodic task and deviants in the non-melodic task (melodic > non-melodic) revealed additional activity in the right inferior parietal lobule. Activation in the inferior parietal lobule likely represents processes related to the maintenance of tonal pitch structure in working memory during pitch discrimination.

Recognition of Frequency Modulated Whistle-Like Sounds by a Bottlenose Dolphin (Tursiops truncatus) and Humans with Transformations in Amplitude, Duration and Frequency

Bottlenose dolphins (Tursiops truncatus) use the frequency contour of whistles produced by conspecifics for individual recognition. Here we tested a bottlenose dolphin's (Tursiops truncatus) ability to recognize frequency modulated whistle-like sounds using a three alternative matching-to-sample paradigm. The dolphin was first trained to select a specific object (object A) in response to a specific sound (sound A) for a total of three object-sound associations. The sounds were then transformed by amplitude, duration, or frequency transposition while still preserving the frequency contour of each sound. For comparison purposes, 30 human participants completed an identical task with the same sounds, objects, and training procedure. The dolphin's ability to correctly match objects to sounds was robust to changes in amplitude with only a minor decrement in performance for short durations. The dolphin failed to recognize sounds that were frequency transposed by plus or minus ½ octaves. Human participants demonstrated robust recognition with all acoustic transformations. The results indicate that this dolphin's acoustic recognition of whistle-like sounds was constrained by absolute pitch. Unlike human speech, which varies considerably in average frequency, signature whistles are relatively stable in frequency, which may have selected for a whistle recognition system invariant to frequency transposition.

Varying irrelevant phonetic features hinders learning of the feature being trained

Learning to distinguish nonnative words that differ in a critical phonetic feature can be difficult. Speech training studies typically employ methods that explicitly direct the learner's attention to the relevant nonnative feature to be learned. However, studies on vision have demonstrated that perceptual learning may occur implicitly, by exposing learners to stimulus features, even if they are irrelevant to the task, and it has recently been suggested that this task-irrelevant perceptual learning framework also applies to speech. In this study, subjects took part in a seven-day training regimen to learn to distinguish one of two nonnative features, namely, voice onset time or lexical tone, using explicit training methods consistent with most speech training studies. Critically, half of the subjects were exposed to stimuli that varied not only in the relevant feature, but in the irrelevant feature as well. The results showed that subjects who were trained with stimuli that varied in the relevant feature and held the irrelevant feature constant achieved the best learning outcomes. Varying both features hindered learning and generalization to new stimuli.

Pitch and spectral resolution: A systematic comparison of bottom-up cues for top-down repair of degraded speech

The brain is capable of restoring missing parts of speech, a top-down repair mechanism that enhances speech understanding in noisy environments. This enhancement can be quantified using the phonemic restoration paradigm, i.e., the improvement in intelligibility when silent interruptions of interrupted speech are filled with noise. Benefit from top-down repair of speech differs between cochlear implant (CI) users and normal-hearing (NH) listeners. This difference could be due to poorer spectral resolution and/or weaker pitch cues inherent to CI transmitted speech. In CIs, those two degradations cannot be teased apart because spectral degradation leads to weaker pitch representation. A vocoding method was developed to evaluate independently the roles of pitch and spectral resolution for restoration in NH individuals. Sentences were resynthesized with different spectral resolutions and with either retaining the original pitch cues or discarding them all. The addition of pitch significantly improved restoration only at six-bands spectral resolution. However, overall intelligibility of interrupted speech was improved both with the addition of pitch and with the increase in spectral resolution. This improvement may be due to better discrimination of speech segments from the filler noise, better grouping of speech segments together, and/or better bottom-up cues available in the speech segments.

Vocal imitations of basic auditory features

Describing complex sounds with words is a difficult task. In fact, previous studies have shown that vocal imitations of sounds are more effective than verbal descriptions [Lemaitre and Rocchesso (2014). J. Acoust. Soc. Am. 135, 862-873]. The current study investigated how vocal imitations of sounds enable their recognition by studying how two expert and two lay participants reproduced four basic auditory features: pitch, tempo, sharpness, and onset. It used 4 sets of 16 referent sounds (modulated narrowband noises and pure tones), based on 1 feature or crossing 2 of the 4 features. Dissimilarity rating experiments and multidimensional scaling analyses confirmed that listeners could accurately perceive the four features composing the four sets of referent sounds. The four participants recorded vocal imitations of the four sets of sounds. Analyses identified three strategies: (1) Vocal imitations of pitch and tempo reproduced faithfully the absolute value of the feature; (2) Vocal imitations of sharpness transposed the feature into the participants' registers; (3) Vocal imitations of onsets categorized the continuum of onset values into two discrete morphological profiles. Overall, these results highlight that vocal imitations do not simply mimic the referent sounds, but seek to emphasize the characteristic features of the referent sounds within the constraints of human vocal production.

Mandarin speech-in-noise and tone recognition using vocoder simulations of the temporal limits encoder for cochlear implants

Temporal envelope-based signal processing strategies are widely used in cochlear-implant (CI) systems. It is well recognized that the inability to convey temporal fine structure (TFS) in the stimuli limits CI users' performance, but it is still unclear how to effectively deliver the TFS. A strategy known as the temporal limits encoder (TLE), which employs an approach to derive the amplitude modulator to generate the stimuli coded in an interleaved-sampling strategy, has recently been proposed. The TLE modulator contains information related to the original temporal envelope and a slow-varying TFS from the band signal. In this paper, theoretical analyses are presented to demonstrate the superiority of TLE compared with two existing strategies, the clinically available continuous-interleaved-sampling (CIS) strategy and the experimental harmonic-single-sideband-encoder strategy. Perceptual experiments with vocoder simulations in normal-hearing listeners are conducted to compare the performance of TLE and CIS on two tasks (i.e., Mandarin speech reception in babble noise and tone recognition in quiet). The performance of the TLE modulator is mostly better than (for most tone-band vocoders) or comparable to (for noise-band vocoders) the CIS modulator on both tasks. This work implies that there is some potential for improving the representation of TFS with CIs by using a TLE strategy.

The effect of presentation level on spectral weights for sentences

Psychophysical data indicate that spectral weights tend to increase with increasing presentation level at high frequencies. The present study examined whether spectral weights for speech perception are similarly affected by presentation level. Stimuli were sentences filtered into five contiguous frequency bands and presented at each of two levels (75 and 95 dB sound pressure level [SPL]). For the highest band (2807-10,000 Hz), normal-hearing listeners' weights were higher for the higher presentation level. Weights for the 95-dB-SPL level resembled those previously estimated for hearing-impaired listeners tested at comparably high levels, suggesting that hearing loss itself may not play a large role in spectral weighting for a sentence recognition task.