Biomedical subjects

Qian-Jie Fu

Publications and source records attributed to Qian-Jie Fu.

4 recordsLinked to original sources

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↗

PubMed2002

Perceptual learning following changes in the frequency-to-electrode assignment with the Nucleus-22 cochlear implant.

The goal of the present study was to investigate the time course of adaptation by experienced cochlear implant users to a shifted frequency-to-electrode assignment in their speech processors. Speech recognition performance of three Nucleus-22 cochlear implant users was measured over a 3-month period, during which the implant listeners continuously wore "experimental" speech processors that were purposely shifted by 2-4 mm in terms of the frequency-to-electrode assignment relative to their normal processor. Baseline speech performance was measured with each subject's clinically assigned speech processor just prior to implementation of the experimental processor. Baseline speech performance was measured again after the 3-month test period, immediately following the reinstallation of the clinically assigned processor settings. Speech performance with the experimental processor was measured four times during the first week, and weekly thereafter over the 3-month period. Results showed that the experimental processor produced significantly lower performance on all measures of speech recognition immediately following implementation. Over the 3-month test period, consonant and HINT sentence recognition with the experimental processors gradually approached a performance level comparable to but still significantly below the baseline and postexperiment measures made with the clinically assigned processor. However, vowel and TIMIT sentence recognition with the experimental processors remained far below the level of the baseline measures even at the end of the 3-month experimental period. There was no significant change in performance with the clinically assigned processor before or after fitting with the experimental processor. The results suggest that a long-time exposure to a new pattern of stimulation may not be able to compensate for the deficit in performance caused by a 2-4-mm shift in the tonotopic location of stimulation, at least within a 3-month period.

Adult↗