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Qian-Jie Fu

Publications and source records attributed to Qian-Jie Fu.

At least 19 recordsLinked to original sources
PubMed2006

Perceptual adaptation to spectrally shifted vowels: training with nonlexical labels.

Although normal-hearing (NH) and cochlear implant (CI) listeners are able to adapt to spectrally shifted speech to some degree, auditory training has been shown to provide more complete and/or accelerated adaptation. However, it is unclear whether listeners use auditory and visual feedback to improve discrimination of speech stimuli, or to learn the identity of speech stimuli. The present study investigated the effects of training with lexical and nonlexical labels on NH listeners' perceptual adaptation to spectrally degraded and spectrally shifted vowels. An eight-channel sine wave vocoder was used to simulate CI speech processing. Two degrees of spectral shift (moderate and severe shift) were studied with three training paradigms, including training with lexical labels (i.e., "hayed," "had," "who'd," etc.), training with nonlexical labels (i.e., randomly assigned letters "f," "b," "g," etc.), and repeated testing with lexical labels (i.e., "test-only" paradigm without feedback). All training and testing was conducted over 5 consecutive days, with two to four training exercises per day. Results showed that with the test-only paradigm, lexically labeled vowel recognition significantly improved for moderately shifted vowels; however, there was no significant improvement for severely shifted vowels. Training with nonlexical labels significantly improved the recognition of nonlexically labeled vowels for both shift conditions; however, this improvement failed to generalize to lexically labeled vowel recognition with severely shifted vowels. Training with lexical labels significantly improved lexically labeled vowel recognition with severely shifted vowels. These results suggest that storage and retrieval of speech patterns in the central nervous system is somewhat robust to tonotopic distortion and spectral degradation. Although training with nonlexical labels may improve discrimination of spectrally distorted peripheral patterns, lexically meaningful feedback is needed to identify these peripheral patterns. The results also suggest that training with lexically meaningful feedback may be beneficial to CI users, especially patients with shallow electrode insertion depths.

Adaptation, Physiological↗
PubMed2006

Recognition of simulated telephone speech by cochlear implant users.

PURPOSE: To evaluate cochlear implant users' understanding of telephone speech. METHOD: Telephone speech was simulated by band-limiting broadband speech stimuli. Multitalker vowel, consonant, and sentence recognition was measured for both simulated telephone speech and broadband speech in 10 postlingually deafened adult cochlear implant users. The study was approved by the St. Vincent's Hospital institutional review board, and signed, informed consent was obtained from all participants. RESULTS: There was no significant difference in vowel recognition scores between broadband and telephone speech. However, mean consonant and sentence recognition scores were significantly poorer with telephone speech. CONCLUSIONS: The limited telephone bandwidth significantly reduced cochlear implant users' understanding of telephone speech. The effect of band-limited speech was highly variable, suggesting that the contribution of high-frequency information to speech recognition varied significantly among the cochlear implant users.

Adult↗
PubMed2006

Contribution of low-frequency acoustic information to Chinese speech recognition in cochlear implant simulations.

Chinese sentence recognition strongly relates to the reception of tonal information. For cochlear implant (CI) users with residual acoustic hearing, tonal information may be enhanced by restoring low-frequency acoustic cues in the nonimplanted ear. The present study investigated the contribution of low-frequency acoustic information to Chinese speech recognition in Mandarin-speaking normal-hearing subjects listening to acoustic simulations of bilaterally combined electric and acoustic hearing. Subjects listened to a 6-channel CI simulation in one ear and low-pass filtered speech in the other ear. Chinese tone, phoneme, and sentence recognition were measured in steady-state, speech-shaped noise, as a function of the cutoff frequency for low-pass filtered speech. Results showed that low-frequency acoustic information below 500 Hz contributed most strongly to tone recognition, while low-frequency acoustic information above 500 Hz contributed most strongly to phoneme recognition. For Chinese sentences, speech reception thresholds (SRTs) improved with increasing amounts of low-frequency acoustic information, and significantly improved when low-frequency acoustic information above 500 Hz was preserved. SRTs were not significantly affected by the degree of spectral overlap between the CI simulation and low-pass filtered speech. These results suggest that, for CI patients with residual acoustic hearing, preserving low-frequency acoustic information can improve Chinese speech recognition in noise.

Acoustic Stimulation↗
PubMed2005

Effects of stimulation mode, level and location on forward-masked excitation patterns in cochlear implant patients.

In multi-channel cochlear implants, electrical current is delivered to appropriate electrodes in the cochlea to approximate the spatial representation of speech. Theoretically, electrode configurations that restrict the current spread within the cochlea (e.g., bi- or tri-polar stimulation) may provide better spatial selectivity, and in turn, better speech recognition than configurations that produce a broader current spread (e.g., monopolar stimulation). However, the effects of electrode configuration on supra-threshold excitation patterns have not been systematically studied in cochlear implant patients. In the present study, forward-masked excitation patterns were measured in cochlear implant patients as functions of stimulation mode, level and location within the cochlea. All stimuli were 500 pulses-per-second biphasic pulse trains (200 micros/phase, 20 micros inter-phase gap). Masker stimuli were 200 ms in duration; the bi-polar configuration was varied from narrow (BP+1) to wide (BP+17), depending on the test condition. Probe stimuli were 20 ms in duration and the masker-probe delay was 5 ms; the probe configuration was fixed at BP+1. The results indicated that as the distance between the active and return electrodes in a bi-polar pair was increased, the excitation pattern broadened within the cochlea. When the distance between active and return electrodes was sufficiently wide, two peaks were often observed in the excitation pattern, comparable to non-overlapping electric fields produced by widely separated dipoles. Analyses of the normalized data showed little effect of stimulation level on the shape of the excitation pattern.

Adult↗
PubMed2005

Auditory training with spectrally shifted speech: implications for cochlear implant patient auditory rehabilitation.

After implantation, postlingually deafened cochlear implant (CI) patients must adapt to both spectrally reduced and spectrally shifted speech, due to the limited number of electrodes and the limited length of the electrode array. This adaptation generally occurs during the first three to six months of implant use and may continue for many years. To see whether moderate speech training can accelerate this learning process, 16 naïve, normal-hearing listeners were trained with spectrally shifted speech via an eight-channel acoustic simulation of CI speech processing. Baseline vowel and consonant recognition was measured for both spectrally shifted and unshifted speech. Short daily training sessions were conducted over five consecutive days, using four different protocols. For the test-only protocol, no improvement was seen over the five-day period. Similarly, sentence training provided little benefit for vowel recognition. However, after five days of targeted phoneme training, subjects' recognition of spectrally shifted vowels significantly improved in most subjects. This improvement did not generalize to the spectrally unshifted vowel and consonant tokens, suggesting that subjects adapted to the specific spectral shift, rather than to the eight-channel processing in general. Interestingly, significant improvement was also observed for the recognition of spectrally shifted consonants. The largest improvement was observed with targeted vowel contrast training, which did not include any explicit consonant training. These results suggest that targeted phoneme training can accelerate adaptation to spectrally shifted speech. Given these results with normal-hearing listeners, auditory rehabilitation tools that provide targeted phoneme training may be effective in improving the speech recognition performance of adult CI users.

Adult↗
PubMed2005

Noise susceptibility of cochlear implant users: the role of spectral resolution and smearing.

The latest-generation cochlear implant devices provide many deaf patients with good speech recognition in quiet listening conditions. However, speech recognition deteriorates rapidly as the level of background noise increases. Previous studies have shown that, for cochlear implant users, the absence of fine spectro-temporal cues may contribute to poorer performance in noise, especially when the noise is dynamic (e.g., competing speaker or modulated noise). Here we report on sentence recognition by cochlear implant users and by normal-hearing subjects listening to an acoustic simulation of a cochlear implant, in the presence of steady or square-wave modulated speech-shaped noise. Implant users were tested using their everyday, clinically assigned speech processors. In the acoustic simulation, normal-hearing listeners were tested for different degrees of spectral resolution (16, eight, or four channels) and spectral smearing (carrier filter slopes of -24 or -6 dB/octave). For modulated noise, normal-hearing listeners experienced significant release from masking when the original, unprocessed speech was presented (which preserved the spectro-temporal fine structure), while cochlear implant users experienced no release from masking. As the spectral resolution was reduced, normal-hearing listeners' release from masking gradually diminished. Release from masking was further reduced as the degree of spectral smearing increased. Interestingly, the mean speech recognition thresholds of implant users were very close to those of normal-hearing subjects listening to four-channel spectrally smeared noise-band speech. Also, the best cochlear implant listeners performed like normal-hearing subjects listening to eight- to 16-channel spectrally smeared noise-band speech. These findings suggest that implant users' susceptibility to noise may be caused by the reduced spectral resolution and the high degree of spectral smearing associated with channel interaction. Efforts to improve the effective number of spectral channels as well as reduce channel interactions may improve implant performance in noise, especially for temporally modulated noise.

Acoustic Stimulation↗
PubMed2005

Effects of stimulation rate, mode and level on modulation detection by cochlear implant users.

In cochlear implant (CI) patients, temporal processing is often poorest at low listening levels, making perception difficult for low-amplitude temporal cues that are important for consonant recognition and/or speech perception in noise. It remains unclear how speech processor parameters such as stimulation rate and stimulation mode may affect temporal processing, especially at low listening levels. The present study investigated the effects of these parameters on modulation detection by six CI users. Modulation detection thresholds (MDTs) were measured as functions of stimulation rate, mode, and level. Results show that for all stimulation rate and mode conditions, modulation sensitivity was poorest at quiet listening levels, consistent with results from previous studies. MDTs were better with the lower stimulation rate, especially for quiet-to-medium listening levels. Stimulation mode had no significant effect on MDTs. These results suggest that, although high stimulation rates may better encode temporal information and widen the electrode dynamic range, CI patients may not be able to access these enhanced temporal cues, especially at the lower portions of the dynamic range. Lower stimulation rates may provide better recognition of weak acoustic envelope information.

Acoustic Stimulation↗
PubMed2005

Loudness growth in cochlear implants: effect of stimulation rate and electrode configuration.

In cochlear implant speech processor design, acoustic amplitudes are mapped to electric currents with the intention of preserving loudness relationships across electrodes. Many parameters may affect the growth of loudness with electrical stimulation. The present study measured the effects of stimulation rate and electrode configuration on loudness growth in six Nucleus-22 cochlear implant users. Loudness balance functions were measured for stimuli that differed in terms of stimulation rate, electrode configuration and electrode location; a 2-alternative, forced-choice adaptive procedure (double-staircase) was used. First, subjects adaptively adjusted the amplitude of a 100-pulse-per-second (pps) pulse train to match the loudness of a 1000-pps standard pulse train. For a range of reference stimulation levels, the loudness of the 100-pps stimulus was matched to that of the 1000-pps standard stimulus; loudness balancing was performed for three electrode pairs [(20,22), (1,3), (1,22)]. The results showed that the loudness balance functions between the 100- and 1000-pps stimulation rates were highly subject-dependent. Some subjects' loudness balance functions were logarithmic, while others' were nearly linear. Loudness balance functions were also measured across electrode locations [(20,22) vs. (1,3)] for two stimulation rates (100, 1000 pps). Results showed that the loudness balance functions between the apical and basal electrode pairs highly depended on the stimulation rate. For all subjects, at the 1000-pps rate, the loudness balance functions between the two electrode locations were nearly linear; however, at the 100-pps rate, the loudness balance function was highly nonlinear in two out of six subjects. These results suggest that, for some cochlear implant patients, low-frequency stimulation may be processed differently at different electrode locations; for these patients, acoustic-to-electric amplitude mapping may need to be sensitive to this place-dependent processing when relatively low stimulation rates are used.

Adult↗
PubMed2005

Speaker normalization for chinese vowel recognition in cochlear implants.

Because of the limited spectra-temporal resolution associated with cochlear implants, implant patients often have greater difficulty with multitalker speech recognition. The present study investigated whether multitalker speech recognition can be improved by applying speaker normalization techniques to cochlear implant speech processing. Multitalker Chinese vowel recognition was tested with normal-hearing Chinese-speaking subjects listening to a 4-channel cochlear implant simulation, with and without speaker normalization. For each subject, speaker normalization was referenced to the speaker that produced the best recognition performance under conditions without speaker normalization. To match the remaining speakers to this "optimal" output pattern, the overall frequency range of the analysis filter bank was adjusted for each speaker according to the ratio of the mean third formant frequency values between the specific speaker and the reference speaker. Results showed that speaker normalization provided a small but significant improvement in subjects' overall recognition performance. After speaker normalization, subjects' patterns of recognition performance across speakers changed, demonstrating the potential for speaker-dependent effects with the proposed normalization technique.

Artificial Intelligence↗
PubMed2005

Voice gender identification by cochlear implant users: the role of spectral and temporal resolution.

The present study explored the relative contributions of spectral and temporal information to voice gender identification by cochlear implant users and normal-hearing subjects. Cochlear implant listeners were tested using their everyday speech processors, while normal-hearing subjects were tested under speech processing conditions that simulated various degrees of spectral resolution, temporal resolution, and spectral mismatch. Voice gender identification was tested for two talker sets. In Talker Set 1, the mean fundamental frequency values of the male and female talkers differed by 100 Hz while in Talker Set 2, the mean values differed by 10 Hz. Cochlear implant listeners achieved higher levels of performance with Talker Set 1, while performance was significantly reduced for Talker Set 2. For normal-hearing listeners, performance was significantly affected by the spectral resolution, for both Talker Sets. With matched speech, temporal cues contributed to voice gender identification only for Talker Set 1 while spectral mismatch significantly reduced performance for both Talker Sets. The performance of cochlear implant listeners was similar to that of normal-hearing subjects listening to 4-8 spectral channels. The results suggest that, because of the reduced spectral resolution, cochlear implant patients may attend strongly to periodicity cues to distinguish voice gender.

Adult↗
PubMed2004

The role of spectral and temporal cues in voice gender discrimination by normal-hearing listeners and cochlear implant users.

The present study investigated the relative importance of temporal and spectral cues in voice gender discrimination and vowel recognition by normal-hearing subjects listening to an acoustic simulation of cochlear implant speech processing and by cochlear implant users. In the simulation, the number of speech processing channels ranged from 4 to 32, thereby varying the spectral resolution; the cutoff frequencies of the channels' envelope filters ranged from 20 to 320 Hz, thereby manipulating the available temporal cues. For normal-hearing subjects, results showed that both voice gender discrimination and vowel recognition scores improved as the number of spectral channels was increased. When only 4 spectral channels were available, voice gender discrimination significantly improved as the envelope filter cutoff frequency was increased from 20 to 320 Hz. For all spectral conditions, increasing the amount of temporal information had no significant effect on vowel recognition. Both voice gender discrimination and vowel recognition scores were highly variable among implant users. The performance of cochlear implant listeners was similar to that of normal-hearing subjects listening to comparable speech processing (4-8 spectral channels). The results suggest that both spectral and temporal cues contribute to voice gender discrimination and that temporal cues are especially important for cochlear implant users to identify the voice gender when there is reduced spectral resolution.

Adult↗
PubMed2004

The number of spectral channels required for speech recognition depends on the difficulty of the listening situation.

Cochlear implants provide a limited number of electrodes, each of which represents a channel of spectral information. Studies have shown that implant recipients are not receiving all of the information from the channels presented to their implant. The present paper provides a quantitative framework for evaluating how many spectral channels of information are necessary for speech recognition. Speech and melody recognition data from previous studies with cochlear implant simulations are compared as a function of the number of spectral channels of information. A quantitative model is applied to the results. Speech recognition performance increases as the number of spectral channels increases. A sigmoid function best describes this increase when plotted as a function of the log number of channels. As speech materials become more difficult, the function shifts to the right, indicating that more spectral channels of information are required. A model proposed by Plomp provides a single index to relate the difficulty of the task to the number of spectral channels needed for moderate recognition performance. In conclusion, simple sentence recognition in quiet can be achieved with only 3-4 channels of spectral information, while more complex materials can require 30 or more channels for an equivalent level of performance. The proposed model provides a single index that not only quantifies the number of functional channels in a cochlear implant, but also predicts the level of performance for different listening tasks.

Audiometry, Speech↗
PubMed2004

Effects of speech processing strategy on Chinese tone recognition by nucleus-24 cochlear implant users.

OBJECTIVE: To evaluate the effects of speech processing strategy on Chinese tone recognition by Nucleus-24 cochlear implant users. METHODS: Recognition of Chinese tones was measured with the spectral peak (SPEAK), advanced combination encoders (ACE), and continuous interleaved sampling (CIS) strategies in nine Nucleus-24 cochlear implant users. Recognition of Chinese sentences was also measured with the ACE strategy (1200 pulse-per-sec on each electrode). As the stimulation rate in the SPEAK processor is fixed at 250 pulses per sec per electrode (ppspe), only one stimulation rate was tested with the SPEAK processor. Three stimulation rates (900, 1200, and 1800 ppspe) were tested in the ACE processing conditions. Four stimulation rates (1200, 1800, 2400, and 3600 ppspe) were tested in the CIS processing conditions. Because the number of stimulating electrodes determines the stimulation rate in CIS processors, the number of electrodes was reduced from 12 to 8 to 6 to 4 to achieve stimulation rates of 1200, 1800, 2400, to 3600 pps. RESULTS: Results showed that mean Chinese tone recognition scores with the ACE and CIS strategies were significantly higher than those with the SPEAK strategy. For the ACE strategy, there was no significant difference in performance among the various stimulation rates (for the ACE processing conditions, the stimulation rate was varied while keeping the number of stimulating electrodes constant). For the CIS strategy, there was no significant difference among the various stimulation rates and electrode configurations (for the CIS processing conditions, the stimulation rate was varied by changing the number of stimulating electrodes). There was also a significant correlation between Chinese tone recognition and the recognition of everyday sentences. CONCLUSIONS: The latest-generation speech processing strategies were able to provide cochlear implant users with considerable amounts of tonal information. However, Chinese tone recognition was significantly affected by the choice in speech processing strategy. Relatively higher stimulation rates (>900 ppspe) may improve Chinese tone recognition. Furthermore, it may be necessary to develop speech processing strategies to specifically improve tone recognition, which is critical for understanding tonal languages.

Adult↗
PubMed2004

Enhancing Chinese tone recognition by manipulating amplitude envelope: implications for cochlear implants.

Tone recognition is important for speech understanding in tonal languages such as Mandarin Chinese. Cochlear implant patients are able to perceive some tonal information by using temporal cues such as periodicity-related amplitude fluctuations and similarities between the fundamental frequency (F0) contour and the amplitude envelope. The present study investigates whether modifying the amplitude envelope to better resemble the F0 contour can further improve tone recognition in multichannel cochlear implants. Chinese tone and vowel recognition were measured for six native Chinese normal-hearing subjects listening to a simulation of a four-channel cochlear implant speech processor with and without amplitude envelope enhancement. Two algorithms were proposed to modify the amplitude envelope to more closely resemble the F0 contour. In the first algorithm, the amplitude envelope as well as the modulation depth of periodicity fluctuations was adjusted for each spectral channel. In the second algorithm, the overall amplitude envelope was adjusted before multichannel speech processing, thus reducing any local distortions to the speech spectral envelope. The results showed that both algorithms significantly improved Chinese tone recognition. By adjusting the overall amplitude envelope to match the F0 contour before multichannel processing, vowel recognition was better preserved and less speech-processing computation was required. The results suggest that modifying the amplitude envelope to more closely resemble the F0 contour may be a useful approach toward improving Chinese-speaking cochlear implant patients' tone recognition.

Adult↗
PubMed2003

The effects of short-term training for spectrally mismatched noise-band speech.

The present study examined the effects of short-term perceptual training on normal-hearing listeners' ability to adapt to spectrally altered speech patterns. Using noise-band vocoder processing, acoustic information was spectrally distorted by shifting speech information from one frequency region to another. Six subjects were tested with spectrally shifted sentences after five days of practice with upwardly shifted training sentences. Training with upwardly shifted sentences significantly improved recognition of upwardly shifted speech; recognition of downwardly shifted speech was nearly unchanged. Three subjects were later trained with downwardly shifted speech. Results showed that the mean improvement was comparable to that observed with the upwardly shifted training. In this retrain and retest condition, performance was largely unchanged for upwardly shifted sentence recognition, suggesting that these listeners had retained some of the improved speech perception resulting from the previous training. The results suggest that listeners are able to partially adapt to a spectral shift in acoustic speech patterns over the short-term, given sufficient training. However, the improvement was localized to where the spectral shift was trained, as no change in performance was observed for spectrally altered speech outside of the trained regions.

Adult↗
PubMed2002

Temporal processing and speech recognition in cochlear implant users.

Although the speech recognition performance of cochlear implant patients has steadily improved in recent years, considerable variability remains in implant patient outcomes. Here, we report on a correlation between cochlear implant patients' auditory temporal processing and speech recognition abilities. Modulation detection thresholds were measured as a function of stimulation level; phoneme recognition was also assessed. Results showed marked individual differences in the shape and absolute sensitivity of subjects' modulation threshold functions. Statistical analysis revealed a strong correlation between phoneme recognition scores and subjects' mean modulation thresholds, demonstrating the contribution of temporal processing to implant speech perception. In correlating a basic psychophysical measure to speech performance, these results should contribute toward improved speech processor design and rehabilitation tools for cochlear implant patients.

Acoustic Stimulation↗
PubMed2002

Frequency mapping in cochlear implants.

OBJECTIVE: To understand the short-term ("acute") effects of parametric variations to the frequency-to-electrode mapping on phoneme identification by Nucleus-22 cochlear implant listeners. METHODS: Phoneme recognition was measured in five Nucleus-22 cochlear implant listeners using custom four-channel continuous interleaved sampler (CIS) processors. For the four-channel processors, speech signals were band-pass filtered into four broad frequency bands. The temporal envelope in each band was extracted by half-wave rectification and low-pass filtering at 160 Hz. The extracted envelope was then transformed to electric currents by a power function with an exponent of 0.2. The resulting electric currents were delivered to four electrode pairs (18,22), (13,17), (8,12), (3,7). The effect of frequency-to-electrode mapping was investigated by systematically varying the parameters of band-pass filters while fixing the electrode locations. Experiment 1 measured phoneme recognition as a function of the slope of band-pass filters. The slope of band-pass filters varied from 48 dB/octave to 6 dB/octave; the corner frequencies of band-pass filters were not varied. Experiment 2 measured phoneme recognition as a function of the distribution of band-pass filters across a fixed overall frequency range. The frequency divisions of a fixed overall frequency range were systematically varied from a logarithmic to a linear distribution. Experiment 3 measured phoneme recognition as a function of the bandwidth of the band-pass filters. The bandwidth of each filter varied from 0.2 to 2 octaves; the center frequencies for each band were not varied. No practice or feedback was provided for subjects in all experiments. RESULTS: The slope of the band-pass filters had little effect on both vowel and consonant recognition. A slight performance drop was observed for only the shallowest slope condition (6 dB/octave). In contrast, the distribution of the band-pass filters had a strong effect on vowel recognition but a weak effect on consonant recognition. Best performance was achieved when a logarithmic or near-logarithmic frequency distribution was used to divide the overall frequency range. The bandwidth of the band-pass filters had a moderate effect on both vowel and consonant recognition. Vowel scores dropped significantly when the bandwidth of filters was too broad, whereas consonant scores dropped significantly when a narrower bandwidth was used. CONCLUSION: Under "acute" testing conditions, phoneme recognition with a four-channel CIS strategy seems to be only mildly affected by the slope of the band-pass filters, but can be significantly affected by the distribution of filters as well as the bandwidth of the filters. Optimal or near-optimal performance can be achieved with a logarithmic frequency distribution. Vowels are more susceptible to broad bandwidths, whereas consonants are more susceptible to narrow bandwidths.

Adult↗