Biomedical subjects

R W Kortekaas

Publications and source records attributed to R W Kortekaas.

5 recordsLinked to original sources

PubMed2000

Bandwidth effects on children's perception of the inflectional morpheme /s/: acoustical measurements, auditory detection, and clarity rating.

The goal of this study was to examine developmental effects in auditory perception of word-final /s/ in inflectional morpheme contexts as a function of high-frequency (HF) bandwidth. Such developmental effects may support the use of hearing aids with extended bandwidths in young children with impaired hearing. The first part of the study consisted of acoustical measurements on word-initial /s/ and inflectional morpheme /s/ in sentences recorded from a male speaker. For this speaker, recordings of inflectional morpheme /s/ on average were approximately 50 ms shorter and about 5 dB lower in level than word-initial /s/ sounds. They also had a lower spectral center of gravity, but not a higher coefficient of kurtosis. The second part consisted of measurements of psychometric functions relating detection of the inflectional morpheme /s/ sounds to HF bandwidth in normally hearing 5-, 7-, and 10-year-old children and adults. In speech-shaped noise, significant main effects of age were found for detection as a function of bandwidth for both the 30- and 10-dB signal-to-noise ratio (SNR) condition, although there was no interaction between age and SNR condition. The third part consisted of subjective clarity rating as a function of HF bandwidth for the same speech stimuli used in the second part. No differences were found between age groups in the shape of the clarity rating functions, but differences were found in the rating variance. No systematic effects of the spectral composition of inflectional morpheme /s/ sounds on either detection or clarity rating were found. The higher detection thresholds and larger clarity rating variances for the youngest participants support the use of extended high-frequency bandwidths for young children with impaired hearing. The extent to which the potential benefit of extended bandwidths is affected by hearing impairment in this population, however, deserves further investigation.

Child↗

PubMed2000

The relation between stimulus context, speech audibility, and perception for normal-hearing and hearing-impaired children.

In this study, the influence of stimulus context and audibility on sentence recognition was assessed in 60 normal-hearing children, 23 hearing-impaired children, and 20 normal-hearing adults. Performance-intensity (PI) functions were obtained for 60 semantically correct and 60 semantically anomalous sentences. For each participant, an audibility index (AI) was calculated at each presentation level, and a logistic function was fitted to rau-transformed percent-correct values to estimate the SPL and AI required to achieve 70% performance. For both types of sentences, there was a systematic age-related shift in the PI functions, suggesting that young children require a higher AI to achieve performance equivalent to that of adults. Improvement in performance with the addition of semantic context was statistically significant only for the normal-hearing 5-year-olds and adults. Data from the hearing-impaired children showed age-related trends that were similar to those of the normal-hearing children, with the majority of individual data falling within the 5th and 95th percentile of normal. The implications of these findings in terms of hearing-aid fitting strategies for young children are discussed.

Acoustic Stimulation↗

PubMed1999

Psychoacoustical evaluation of PSOLA. II. Double-formant stimuli and the role of vocal perturbation.

This article presents the results of listening experiments and psychoacoustical modeling aimed at evaluating the pitch synchronous overlap-and-add (PSOLA) technique. This technique can be used for simultaneous modification of pitch and duration of natural speech, using simple and efficient time-domain operations on the speech waveform. The first set of experiments tested the ability of subjects to discriminate double-formant stimuli, modified in fundamental frequency using PSOLA, from unmodified stimuli. Of the potential auditory discrimination cues induced by PSOLA, cues from the first formant were found to generally dominate discrimination performance. In the second set of experiments the influence of vocal perturbation, i.e., jitter and shimmer, on discriminability of PSOLA-modified single-formant stimuli was determined. The data show that discriminability deteriorates at most modestly in the presence of jitter and shimmer. With the exception of a few conditions, the trends in these data could be replicated by either using a modulation-discrimination or an intensity-discrimination model, dependent on the formant frequency. As a baseline experiment detection thresholds for jitter and shimmer were measured. Thresholds for jitter could be replicated by using either the modulation-discrimination or the intensity-discrimination model, dependent on the (mean) fundamental frequency of stimuli. The thresholds for shimmer could be accurately predicted for stimuli with a 250-Hz fundamental, but less accurately in the case of a 100-Hz fundamental.

Adult↗

PubMed1997

Psychoacoustical evaluation of the pitch-synchronous overlap-and-add speech-waveform manipulation technique using single-formant stimuli.

This article presents two experiments dealing with a psychoacoustical evaluation of the pitch-synchronous overlap-and-add (PSOLA) technique. This technique has been developed for modification of duration and fundamental frequency of speech and is based on simple waveform manipulations. Both experiments were aimed at deriving the sensitivity of the auditory system to the basic distortions introduced by PSOLA. In experiment I, manipulation of fundamental frequency was applied to synthetic single-formant stimuli under minimal stimulus uncertainty, level roving, and formant-frequency roving. In experiment II, the influence of the positioning of the so-called "pitch markers" was studied. Depending on the formant and fundamental frequency, experimental data could be described reasonably well by either a spectral intensity-discrimination model or a temporal model based on detecting changes in modulation of the output of a single auditory filter. Generally, the results were in line with psychoacoustical theory on the auditory processing of resolved and unresolved harmonics.

Adult↗

PubMed1996

Vowel-onset detection by vowel-strength measurement, cochlear-nucleus simulation, and multilayer perceptrons.

An algorithm for detection of vowel onsets in fluent speech was presented by Hermes [j. Acoust. Soc. Am. 87, 866-873 (1990)]. Performance tests showed that detection was good for fluent speech, although the parameter settings had to be modified for application to well-articulated speech. One of the purposes of the algorithm was application to speech by deaf persons, for which it failed completely. In order to improve the algorithm and to make it more generally applicable, two alternative detection strategies have been explored in the present study. These strategies were (a) simulation of transient-chopper responses in the cochlear nucleus and (B) training of multilayer perceptrons. Two large databases of read speech have been used for performance comparison of the original algorithm and the new strategies. The strategy based on simulating cochlear-nucleus responses is found both to result in a higher false-alarm rate than the original algorithm and to be rather level dependent. On the other hand, the performance of a multilayer-perceptron network, trained on mel-scaled spectra, is comparable to the performance of the Hermes algorithm. In more general terms, the results suggest that temporal information on intensity and (rough) spectral envelope are important for human vowel-onset detection behavior. In formation on harmonicity can be used as a secondary source of information to avoid detection of mainly unvoiced, nonvowel onsets.

Algorithms↗