Biomedical subjects

D J Van Tasell

Publications and source records attributed to D J Van Tasell.

At least 19 recordsLinked to original sources

PubMed1997

The Carhart Memorial Lecture, American Auditory Society, Salt Lake City, Utah 1996. Phoneme and word recognition for words in isolation and in sentences.

OBJECTIVE: To evaluate relations among scores for phonemes, words in isolation, and words in sentences for listeners with normal hearing and for listeners with sensorineural hearing loss. DESIGN: Ten-word lists of consonant-vowel-consonant monosyllables with each list utilizing the same 10 vowels and 20 consonants (Boothroyd, 1968) were devised and recorded. These words also were incorporated into contextually correct sentences and recorded by the same talker. The materials were presented in quiet to 36 listeners with normal hearing and to 876 listeners (1260 ears) with sensorineural hearing loss. Formulae derived by Boothroyd and Nittrouer (1988) to relate scores for phonemes, words, and sentences were applied to the data. RESULTS: Phoneme scoring yielded scores that were on the order of 20% higher than scores for whole words heard in isolation, and scores for words in sentences were about 20% higher than when the same words were heard singly. Relations among scores for phonemes, words in isolation, and words in sentences were very similar to those observed by Boothroyd and Nittrouer (1988). The constants derived from application of their formulae to our data were very similar to the constants Boothroyd and Nittrouer obtained for a different set of materials presented against a noise background to listeners with normal hearing. Further, the constants were similar for our group of listeners with normal hearing and our large sample of listeners with sensorineural hearing loss. CONCLUSIONS: 1) These findings support Bilger's (1984) unifying assumptions that speech recognition is a single construct; therefore, scores on all speech recognition tests must be related and scores on one speech recognition test should be predictive of scores on other tests. 2) Advantages of phoneme scoring include: A) It increases the sample size of scored items for a given list of words, thereby reducing variability in test results. B) Statistical equivalence of phoneme scores for the same 30 phonemes in each of two isophonemic word lists can be evaluated quickly and easily by applying the binomial distribution model to the scores (Thornton & Raffin, 1978). C) Phoneme scores are reasonably accurate predictors of recognition of words in the contextually correct but generally low probability sentences used in this study.

Adolescent↗

PubMed1996

Effects of single-band syllabic amplitude compression on temporal speech information in nonsense syllables and in sentences.

The effects of single-band amplitude compression on the use by subjects with normal hearing of temporal speech information were assessed using speech stimuli that had been processed to remove most spectral information before being compressed. The resulting signal-related-noise (SRN) stimuli isolated the effects of compression on the temporal information in speech by making it impossible for subjects to identify stimulus items on the basis of spectral speech information. Subjects with normal hearing listened to /aCa/ SRN disyllables that had been subjected to single-band compression at various combinations of compression ratio (CR) and time constants (TC). Performance was reduced only in the most severe compression condition (CR = 8; TC = 50), and then only slightly. Additional testing showed that subjects could use both periodicity and compression-overshoot artifactual information--in addition to envelope information--to identify the compressed /aCa/ stimuli. When a list of 10 context-controlled sentences was converted to SRN and compressed at CR = 8 and TC = 50, the ability of subjects with normal hearing to identify the sentences was significantly affected. Results established that (a) subjects with normal hearing differ widely in their abilities to use temporal information for speech identification, even after training; (b) subjects can learn to use both temporal envelope and periodicity information for identification if disyllables, even though; (c) subjects with normal hearing need envelope but not periodicity information to identify SRN sentences in a closed set. These results suggest that single-band compression at CR = 8 and TC = 50 would be undesirable for persons with limited ability to resolve speech spectral information. It is currently not known how less severe compression conditions would affect envelope information in sentences.

Adult↗

PubMed1995

Quantifying the relation between speech quality and speech intelligibility.

The purpose of the present research was to examine the relation between speech quality and speech intelligibility. Speech quality measurements were made using continuous discourse and a category rating procedure for the following dimensions: intelligibility, pleasantness, loudness, effort, and total impression. Measurements were made using a group of listeners with normal hearing for a set of stimulus conditions in which intelligibility varied, and for a set of stimulus conditions in which intelligibility was held constant near 100%. When ratings were made for a set of stimulus conditions in which intelligibility was allowed to vary (a) intersubject reliability was high (i.e., different listeners interpreted the dimensions in a similar manner); and (b) the speech quality dimensions of intelligibility, effort, and loudness were indistinguishable. When ratings were made for a set of stimulus conditions in which intelligibility was held constant (a) intersubject reliability was reduced, indicating that different listeners interpreted the dimensions in different ways; (b) most listeners rated each dimension differently, indicating that the dimensions were unique; and (c) across listeners, no single dimension was highly correlated with total impression. These results can be used in order to examine the relation between speech quality and speech intelligibility.

Adult↗

PubMed1995

Measurement of speech quality as a tool to optimize the fitting of a hearing aid.

The purpose of the present research was to develop a theoretical basis for the adjustment of hearing aid frequency response based on speech quality measurements. Speech quality measurements were made using continuous discourse and a category rating procedure for the following dimensions: intelligibility, pleasantness, loudness, effort, noisiness, and total impression. Speech quality ratings were obtained from a group of listeners with hearing loss who wore hearing aids. The stimulus conditions simulated hearing aid frequency response alterations within a frequency response range where intelligibility was held constant at or near 100%. The subject ratings revealed that (a) different listeners interpreted the individual dimensions in different ways; (b) within listeners, most of the dimensions were unique; that is, they were rated differently; and (c) across listeners, pleasantness was the dimension most highly correlated with total impression.

Adult↗

PubMed1995

Electrode ranking of "place pitch" and speech recognition in electrical hearing.

The ability to distinguish electrical stimulation of different electrodes on the basis of "pitch or sharpness" was evaluated with an electrode ranking procedure in 14 individual users of the Nucleus cochlear implant. Prior to the electrode ranking test, absolute thresholds and maximum comfortable loudness levels were measured, and loudness balancing was accomplished across all usable electrodes. Performance on the electrode ranking task was defined in terms of d' per mm of distance between comparison electrodes. Large individual differences were found among cochlear-implant users. In subjects with good to excellent place-pitch sensitivity, the electrode ranking task was limited by a ceiling effect; however, in those with poor to moderate sensitivity d'/mm was relatively constant with spatial separation between electrodes. Place pitch was typically ordered from apical to basal electrodes, i.e., basal electrodes were judged to be higher in pitch than more apical electrodes. However, instances of reversals in place-pitch ordering were seen on some electrodes in some subjects. Instances were also seen of better electrode ranking in the apical half of the electrode array than in the basal half, and vice-versa. Analyses of the electrode ranking functions in terms of d' per stimulus indicated that, in some subjects, perfect performance was reached with as little as 0.75 mm between comparison electrodes, the minimum possible. In other subjects, perfect performance was not reached until the spatial separation between comparison electrodes was over 13 mm, more than three quarters of the entire length of the electrode array. Ten of the subjects also participated in a closed-set recognition task of intervocalic consonants. Although the maximum transmitted information for place of consonant articulation (which is based primarily on spectral speech cues) was only 34%, correlations between place-pitch sensitivity and transmitted speech information were as high as 0.71. This was surprising considering the excellent place-pitch sensitivity exhibited by some of the subjects, and may reflect limitations of the Nucleus speech coding strategy for representing spectrally coded speech information. The two prelingual subjects performed notably poorer on the speech task than the postlingual subjects, even though one of the prelingual subjects demonstrated very good place-pitch sensitivity.

Adult↗

PubMed1994

Effect of peak clipping on speech recognition threshold.

Speech recognition thresholds (SRTs) were measured for a closed set of spondees that had been processed by peak clipping and compression. Both hearing-impaired and normal-hearing subject groups showed progressively higher SRTs with increasing levels of peak clipping, with significant threshold shifts occurring for clipping levels greater than 18 to 24 dB. Neither subject group showed significantly elevated SRTs for the compression processed stimuli. Magnitude-squared coherence analysis of the speech stimuli revealed high levels of distortion generated by peak clipping and relatively low levels generated by the compression processing. Subsequent analysis suggested that the addition of distortion products and not the alteration of the speech waveform envelope was responsible for the observed threshold shifts, and that coherence analysis may be a valuable tool for predicting the effects of distortion on speech intelligibility. Judgments of sound quality showed that the clipping level where SRTs began to be significantly affected coincided with the clipping level at which the quality of the speech was judged to be unacceptable.

Adult↗

PubMed1994

Is useful speech information carried by fibers with high characteristic frequencies?

It has been proposed that auditory-nerve fibers with characteristic frequencies (CFs) above the speech-frequency range are important in speech perception when the signal-to-noise ratio in the speech frequency range is low [S. Greenberg, J. Phon. 16, 139-149 (1988)]. If this is true, then it might be expected that recognition of speech at low signal-to-noise ratios would worsen with the addition of high-pass noise sufficiently intense to mask information in high-CF fibers. This hypothesis was tested for closed-set recognition of vowels and spondees. Recognition was measured as a function of signal-to-noise ratio in speech-shaped noise, with and without an intense high-pass noise. The addition of high-pass noise did not degrade vowel recognition. Spondee recognition decreased with the addition of the high-pass noise at the highest levels of the speech-shaped noise. However, this same decrease was seen when the spondees were low-pass filtered to simulate downward spread of masking by the high-pass noise. This indicates that the decrease in spondee recognition with high-pass noise was due to masking of information in fibers with CFs in the speech range. Overall, these results suggest that fibers whose CFs are above the speech range are not necessary for speech perception in noise or in quiet.

Adult↗

PubMed1994

Robust adaptive microphone array processing for hearing aids: realistic speech enhancement.

The problem of combining the outputs of an array of microphones as a single input for a hearing aid is investigated. Emphasis is placed on the conservative prediction of realistically achievable performance gains provided by the array over a single microphone. Performance improvement is measured as a change in the speech reception threshold (SRT) between single microphone and multimicrophone conditions. Consistent with previous work, predictions of this change in SRT using intelligibility averaged gain, [symbol: see text] are shown to be good. Consequently, this measure is used, along with changes in signal-to-noise ratios (SNRs), to evaluate array performance. The results presented include the effects of acoustic headshadow, small room reverberation, microphone placement uncertainty, and desired speaker location uncertainty. It is in this context that realistic predictions of speech enhancement provided by robust adaptive microphone array processors are discussed. Performance improvements are demonstrated relative to the "best" single microphone in the array for three types of spatial filters: Fixed, robust block processed, and robust adaptive. The performance of the robust block processed arrays is shown to be attainable with adaptive implementations. One fundamental criterion employed in robust beamformer design directly limits the amount of cancellation of the desired signal that can occur.

Adult↗

PubMed1993

Hearing loss, speech, and hearing aids.

Modern hearing aids permit adjustment of a number of electroacoustic parameters, among them frequency response, saturation sound pressure level, and various aspects of compression. Relatively little is known, however, about how the electroacoustic characteristics of hearing aids affect the information-bearing properties of speech. Even less is known about how hearing aids might alleviate or exacerbate the effects of impaired hearing. This article reviews current knowledge in three areas: (a) characteristics of mild/moderate hearing loss, (b) information-bearing aspects of speech, and (c) the relation between electroacoustic characteristics of hearing aids and the speech signal. Concluding suggestions are made regarding the implications of the current data for selecting hearing-aid characteristics.

Acoustic Stimulation↗

PubMed1992

Noise reduction hearing aids: release from masking and release from distortion.

Automatic frequency response (AFR) hearing aids usually reduce their low-frequency gain in the presence of noise; several investigators have reported improved recognition of high-frequency speech information in low-frequency band-limited noise with AFR versus non-AFR hearing aids. In this work, masking patterns (masked threshold for frequency-modulated probe tones as a function of probe frequency) were obtained for a narrowband low-frequency noise. Speech recognition threshold for a set of high-frequency loaded monosyllables also was obtained in the presence of the same noise. Aided speech and masking pattern data for one normal and two hearing-impaired subjects wearing a master hearing aid incorporating a commercially available AFR circuit showed modest AFR effects. Moreover, masking noise spectra measured in ear canals of subjects wearing the master hearing aid showed evidence of substantial hearing aid-generated distortion products in the AFR-off condition. Results obtained from the normal subject listening with a low-distortion laboratory simulation of an AFR hearing aid showed greater release from masking for the same low-frequency attenuation as provided by the hearing aid. Improvements of speech recognition in noise observed with AFR hearing aids may result from some combination of release from upward spread of masking and reduction of distortion products generated by the hearing aid in the non-AFR setting.

Adult↗

PubMed1992

Temporal cues for consonant recognition: training, talker generalization, and use in evaluation of cochlear implants.

Limited consonant phonemic information can be conveyed by the temporal characteristics of speech. In the two experiments reported here, the effects of practice and of multiple talkers on identification of temporal consonant information were evaluated. Naturally produced /aCa/disyllables were used to create "temporal-only" stimuli having instantaneous amplitudes identical to the natural speech stimuli, but flat spectra. Practice improved normal-hearing subjects' identification of temporal-only stimuli from a single talker over that reported earlier for a different group of unpracticed subjects [J. Acoust. Soc. Am. 82, 1152-1161 (1987)]. When the number of talkers was increased to six, however, performance was poorer than that observed for one talker, demonstrating that subjects had been able to learn the individual stimulus items derived from the speech of the single talker. Even after practice, subjects varied greatly in their abilities to extract temporal information related to consonant voicing and manner. Identification of consonant place was uniformly poor in the multiple-talker situation, indicating that for these stimuli consonant place is cued via spectral information. Comparison of consonant identification by users of multi-channel cochlear implants showed that the implant users' identification of temporal consonant information was largely within the range predicted from the normal data. In the instances where the implant users were performing especially well, they were identifying consonant place information at levels well beyond those predicted by the normal-subject data. Comparison of implant-user performance with the temporal-only data reported here can help determine whether the speech information available to the implant user consists of entirely temporal cues, or is augmented by spectral cues.

Adult↗

PubMed1991

Maximum real-ear gain of in-the-ear hearing aids.

Three hearing aid manufacturers provided custom full-shell in-the-ear hearing aids for each of 3 hearing-impaired subjects. Each manufacturer was instructed that the hearing aids should provide the maximum possible acoustic gain within the limits of hearing aid shell size and available components. Coupler gain, insertion gain, and functional gain were measured for each hearing aid. Gain measures were made with the volume control at either the full-on setting or the highest setting possible before the onset of acoustical feedback. Full-on coupler gain curves were similar across all nine hearing aids. Individual differences in concha/ear canal size and in the fit of the hearing aids produced substantial variance in insertion gain across hearing aids. Peak insertion gain varied from 41 to 58 dB. If 10 dB reserve gain is allowed, the range of estimated peak use gain from these maximum-gain in-the-ear hearing aids is 31-48 dB.

Acoustics↗

PubMed1990

Evaluation of an articulation-index based model for predicting the effects of adaptive frequency response hearing aids.

The Articulation Index (AI) was used to evaluate an "adaptive frequency response" (AFR) hearing aid with amplification characteristics that automatically change to become more high-pass with increasing levels of background noise. Speech intelligibility ratings of connected discourse by normal-hearing subjects were predicted well by an empirically derived AI transfer function. That transfer function was used to predict aided speech intelligibility ratings by 12 hearing-impaired subjects wearing a master hearing aid with the Argosy Manhattan Circuit enabled (AFR-on) or disabled (AFR-off). For all subjects, the AI predicted no improvements in speech intelligibility for the AFR-on versus AFR-off condition, and no significant improvements in rated intelligibility were observed. The ability of the AI to predict aided speech intelligibility varied across subjects. However, ratings from every hearing-impaired subject were related monotonically to AI. Therefore, AI calculations may be used to predict relative--but not absolute--levels of speech intelligibility produced under different amplification conditions.

Adult↗

PubMed1987

Representations of the long-term spectra of speech.

Numerous and somewhat different representations of the long-term spectra of speech are available in the literature. Various estimates of speech spectra have been converted to a consistent audiogram format for presentation here. Even so, plots of speech spectral levels across the frequency region of 125 to 8000 Hz vary considerably. Bases for some of these variations and clinical utilization of a speech spectrum are discussed.

Auditory Threshold↗

PubMed1987

Vowel identification and vowel masking patterns of hearing-impaired subjects.

Confusion matrices for seven synthetic steady-state vowels were obtained from ten normal and three hearing-impaired subjects. The vowels were identified at greater than 96% accuracy by the normals, and less accurately by the impaired subjects. Shortened versions of selected vowels then were used as maskers, and vowel masking patterns (VMPs) consisting of forward-masked threshold for sinusoidal probes at all vowel masker harmonics were obtained from the impaired subjects and from one normal subject. Vowel-masked probe thresholds were transformed using growth-of-masking functions obtained with flat-spectrum noise. VMPs of the impaired subjects, relative to those of the normal, were characterized by smaller dynamic range, poorer peak resolution, and poorer preservation of the vowel formant structure. These VMP characteristics, however, did not necessarily coincide with inaccurate vowel recognition. Vowel identification appeared to be related primarily to VMP peak frequencies rather than to the levels at the peaks or to between-peak characteristics of the patterns.

Acoustic Stimulation↗

PubMed1987

Speech waveform envelope cues for consonant recognition.

This study investigated the cues for consonant recognition that are available in the time-intensity envelope of speech. Twelve normal-hearing subjects listened to three sets of spectrally identical noise stimuli created by multiplying noise with the speech envelopes of 19(aCa) natural-speech nonsense syllables. The speech envelope for each of the three noise conditions was derived using a different low-pass filter cutoff (20, 200, and 2000 Hz). Average consonant identification performance was above chance for the three noise conditions and improved significantly with the increase in envelope bandwidth from 20-200 Hz. SINDSCAL multidimensional scaling analysis of the consonant confusions data identified three speech envelope features that divided the 19 consonants into four envelope feature groups ("envemes"). The enveme groups in combination with visually distinctive speech feature groupings ("visemes") can distinguish most of the 19 consonants. These results suggest that near-perfect consonant identification performance could be attained by subjects who receive only enveme and viseme information and no spectral information.

Cochlear Implants↗

PubMed1987

Tone detection and synthetic speech discrimination in band-reject noise by hearing-impaired listeners.

Frequency resolution was evaluated for two normal-hearing and seven hearing-impaired subjects with moderate, flat sensorineural hearing loss by measuring percent correct detection of a 2000-Hz tone as the width of a notch in band-reject noise increased. The level of the tone was fixed for each subject at a criterion performance level in broadband noise. Discrimination of synthetic speech syllables that differed in spectral content in the 2000-Hz region was evaluated as a function of the notch width in the same band-reject noise. Recognition of natural speech consonant/vowel syllables in quiet was also tested; results were analyzed for percent correct performance and relative information transmitted for voicing and place features. In the hearing-impaired subjects, frequency resolution at 2000 Hz was significantly correlated with the discrimination of synthetic speech information in the 2000-Hz region and was not related to the recognition of natural speech nonsense syllables unless (a) the speech stimuli contained the vowel /i/ rather than /a/, and (b) the score reflected information transmitted for place of articulation rather than percent correct.

Adult↗

PubMed1987

Speech recognition threshold in noise: effects of hearing loss, frequency response, and speech materials.

Speech recognition threshold (SRT) was measured in quiet and in noise for normal-hearing subjects and subjects with high-frequency sensorineural hearing loss. For the hearing-impaired subjects, SRT in quiet approximated the amount of hearing loss in the frequency region of importance for each of two sets of speech materials--spondees and monosyllables. With changes in frequency response of the stimulus delivery system, SRT shifted differentially for spondees and monosyllables. The speed, reliability, and apparent sensitivity of the SRT in quiet and noise to frequency response characteristics make it a potentially useful tool for hearing aid evaluation if speech materials appropriate to both the hearing loss configuration and the frequency response of amplification are chosen.

Adult↗