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Biomedical subjects

B W Edwards

Publications and source records attributed to B W Edwards.

11 recordsLinked to original sources
PubMed2000

Lexical boundary error analysis in hypokinetic and ataxic dysarthria.

This investigation is the second in a series to examine a potential source of reduced intelligibility in dysarthric speech, namely the mismatch between listeners' perceptual strategies and the acoustic information available in the dysarthric speech signal. Lexical boundary error (LBE) analysis was conducted on listener transcripts from phrases produced by speakers with hypokinetic dysarthria, ataxic dysarthria, and normal controls. By design, the hypokinetic and ataxic dysarthric tapes elicited similar intelligibility (words-correct) scores. However, they elicited different numbers and patterns of lexical boundary errors. The nature of the error pattern differences can be traced to the listeners' use of available syllabic strength information to segment the acoustic stream. Specifically, although both dysarthric speech samples elicited numerous lexical boundary errors, those for the hypokinetic speech generally conformed to predictions offered from studies of degraded normal speech. Those for the ataxic speech did not conform strongly to such predictions. It appears that the prosodic deficits of the ataxic speech (tendency toward syllabic isochrony, excessive loudness variation, and reduced vowel working space consequent to reductions in vowel strength) posed more of a problem for listeners than did the prosodic deficits of the hypokinetic speech (rapid rate, monotony, reduced vowel working space).

Adolescent↗
PubMed1997

Masking of a brief probe by sinusoidal frequency modulation.

Contrary to level detection models, the thresholds for a brief-duration probe masked by a sinusoidal frequency modulation (FM) masker increases as the modulation index (beta) of FM increases [Zwicker, Acustica 31, 243-256 (1974)]. In this paper the reason for this phenomenon is investigated. In experiment 1, a 10-ms, 1-kHz probe was detected in the presence of an FM masker centered at 1 kHz and sinusoidally modulated at 16 Hz. Thresholds increased by over 15 dB with increasing beta, consistent with Zwicker's findings. In experiment 2, the instantaneous frequency changes of the masker used in experiment 1 were clipped and the resulting thresholds indicated that detection was determined primarily by the masker's total frequency excursion rather than by its instantaneous sweep rate. In experiment 3, the FM maskers from the first two experiments were passed through a roex filter centered at 1 kHz and the resulting envelope was used to amplitude modulate a 1-kHz tone, producing approximately the same effective envelope at 1 kHz as the FM maskers. Threshold functions for the amplitude modulated (AM) maskers were similar to those for their corresponding FM maskers. Thresholds increased by over 15 dB while the total energy of the AM masker decreased by over 10 dB, again contrary to standard level-detection models. The results from these experiments can be explained, at least qualitatively, by a model based on envelope shape discrimination: similarities between the envelopes of the masker alone and masker-plus-probe at the output of an auditory filter centered on the frequency of the probe are primarily responsible for the observed masking, particularly at large beta's.

Auditory Perception↗
PubMed1995

The study of vocal fold vibratory patterns in patients with unilateral vocal fold paralysis before and after type I thyroplasty with or without arytenoid adduction.

Type I thyroplasty and arytenoid adduction have been used for the treatment of symptomatic unilateral vocal fold paralysis since the mid-1970s. To this date, the vibratory patterns of the vocal folds in patients with unilateral vocal fold paralysis undergoing thyroplasty have not been studied in depth. Abnormal vibration of the vocal fold mucosa often contributes to voice problems in persons diagnosed with vocal diseases or disorders. The preoperative and postoperative videostroboscopic vibratory patterns including mucosal wave, amplitude, glottic closure, and symmetry were studied in 12 patients who underwent unilateral type I thyroplasty separately or in combination with an arytenoid adduction. The observed changes and clinical implications are discussed.

Adult↗
PubMed1994

Psychoacoustic equivalence of frequency modulation and quasi-frequency modulation.

Frequency modulation (FM) is known to be reasonably approximated by quasi-frequency modulation (QFM) for small modulation indices, beta, but the range of beta for which this approximation is appropriate is unclear. Thresholds for discrimination between FM and QFM with equal beta's are obtained in order to estimate an upper bound on beta for determining when this approximation is valid psychoacoustically, i.e., when FM and QFM are indiscriminable. At low modulation frequencies (fm < or = 4 Hz), QFM is never a valid approximation to FM at any detectable modulation level since discrimination thresholds are below FM detection thresholds. For modulation frequencies between 8 and 32 Hz, discrimination thresholds are approximately -2.5 dB (20 log beta) and can be accounted for by detection of envelope fluctuations in the QFM signal. For modulation frequencies at 64 Hz and above, discrimination thresholds improve with increasing modulation frequency in the same manner as FM and QFM detection thresholds. Discrimination in this frequency region seems to be mediated by detection of the component 2fm Hz below the carrier, i.e., by the most detectable component in the FM signal which does not occur in the QFM signal.

Adult↗
PubMed1994

Modulation detection and discrimination with three-component signals.

In an attempt to study the processing of amplitude and frequency modulation (AM and FM), detection and discrimination tasks using mixed modulation (MM) signals were performed. Modulation detection thresholds were obtained for three-component signals that span the parameter space between AM and quasi-FM. A single-cue modulation detection model predicts the thresholds with reasonable accuracy. If one assumes that the AM and FM components are extracted separately, thresholds are also well predicted if the d' of the MM signals is equal to the sum of the separate d's of the AM and FM components (two-cue summation model). This could arise from common internal noise that puts the AM and FM information along a single decision axis. A modulation discrimination task was then examined in which the subjects discriminate between signals with both different modulation depths and different modulation types. The single-cue model predicts performance well. In order for the two-cue model to predict the results, the AM and FM cues must be combined into a single statistic before a decision can be made; the listener cannot process the cues separately.

Adult↗
PubMed1994

Frequency modulation versus amplitude modulation discrimination: evidence for a second frequency modulation encoding mechanism.

The encoding mechanisms for amplitude modulation (AM) and frequency modulation (FM) were investigated using AM-FM discrimination tasks. In the first experiment, AM and FM were set at equally detectable levels within a trial, and discrimination thresholds were obtained adaptively in a 3IFC task. Here, AM-FM discrimination thresholds were considerably larger than both AM and FM detection thresholds. This is consistent with an encoding system whereby AM and FM are partially encoded by the same mechanism. In the second experiment, performance on AM-FM discrimination is measured with a fixed-level procedure. Psychometric functions obtained for a constant modulation depth of AM were nonmonotonic with FMs modulation index beta and each displayed a single minimum. The nonmonotonic nature of the functions is consistent with a model in which FM is encoded primarily with the same mechanism that encodes AM but also with a second mechanism, probably related to changes in instantaneous frequency, that is independent of the mechanism that extracts AM. The fact that minima in the discrimination psychometric functions increase from d' = 0 as beta increases indicates that the information encoded by the second mechanism becomes more detectable with increasing beta.

Auditory Perception↗
PubMed1993

The spectral shaping of neural discharges by refractory effects.

It has previously been shown that post-stimulus time (PST) histograms have autoregressive properties, which implies that the neural firings have spectral components that are determined by these properties. The expected power spectral density of neural discharges is derived when the process is firing at a constant rate (similar to tonal stimulation at CF with no phase locking). Although the unconditional intensity of the process is not time varying, the spectrum exhibits prominent spectral peaks. The effect of histogram bin size, stimulus intensity, and refractory effects are examined with respect to spectral shape and it is shown that stimulus intensity determines the magnitude of spectral peaks while refractory duration determines the peak locations. The effectiveness of predicting the spectrum is demonstrated with eight-nerve data and point process simulations.

Acoustic Stimulation↗
PubMedDate not supplied

An efficient method for detecting connectivity in neural ensembles.

Modern technology is allowing researchers to collect data from neural ensembles with a large number of units, and the analysis of interaction between these units can be very time consuming. Estimation of pairwise connectivity is the most common method of determining the neural 'network' but usually necessitates the production of numerous histograms for each pair considered. We present a method which will indicate which pairs in a network represent potential connections and thereby simplify the postexperimental analysis. The technique uses cross-interval information to create an n x n matrix which represents all possible connections in an n neuron ensemble and can be calculated recursively on-line. The performance of this technique is analyzed with respect to data size and strength of the connections. It is compared to 2 similar techniques that are also presented here, one in which perfect knowledge of the timing of the excitation is known, and one in which the timing can be bounded.

Computer Simulation↗