Biomedical subjects

M T Ochs

Publications and source records attributed to M T Ochs.

9 recordsLinked to original sources

PubMed1996

The effect of segment duration on the perceptual integration of nasals for adult and child speech.

It has been hypothesized that the acoustic properties within a temporal domain of 10 to 30 ms of boundaries between speech sounds contain significant information on the phonetic features of segments, and that these cues are perceptually integrated by the auditory system [Stevens, Phonetic Linguistics: Essays in Honor of Peter Ladefoged (Academic, London, 1985)]. The purpose of the current research was to examine the effects of stimulus duration adjacent to speech sound boundaries on the perceptual integration of place of articulation of nasals before and after disruption of the abrupt changes in spectra between the murmur and transition. In experiment I, three children, aged 3, 5, and 7 years, and an adult female and male produced consonant-vowel (CV) syllables consisting of [m] and [n] in four vowel contexts, [i ae u a]. Approximately 25-ms segments of the murmur and vowel transition adjacent to the speech sound boundary were digitally removed from these productions. Intervals of silence ranging from 0 to 2000 ms, which can potentially perturb integration processes, were inserted between these segments. The stimuli were then presented to adult listeners for the identification of the nasal. The main findings revealed a consistent decline in identification with gap durations up to 150 ms across speakers and vowel context. However, the adult labial feature was resistant to perceptual change as a function of gap duration. This result appeared to relate to formant transition duration, and not to response bias. In experiment II, stimuli with durations shorter than those in experiment I were further analyzed for adult speakers. The main finding was a quantification of the acoustic segment duration needed for perceptual integration of the murmur and vowel transition. Across both experiments, the results reveal a decline in the identification of both alveolar and labial nasals within a time interval mediated by short-term auditory memory, and that the duration of the acoustic segment needed for perceptual integration is longer for [n] than [m].

Adult↗

PubMed1996

Consonant recognition performance of hearing-impaired listeners using one linear and three nonlinear hearing aids.

Consonant recognition performance was examined in 18 subjects listening in quiet and speech noise with linear and nonlinear hearing aids. Subjects were divided into three groups by audiometric configuration: flat, moderately sloping, and sharply sloping. Nonlinear amplification schemes included adaptive high-pass filtering (Argosy's Manhattan II, experimentally modified; MANe), MANe circuitry followed by expansion (EXP), and infinite amplitude clipping (IAC). Consonant-to-vowel ratios (CVRs) were calculated for syllables processed through each hearing aid. Performance with the IAC was significantly poorer than with the other amplifiers across audiograms in noise. Intersubject variability in performance was high, even within audiogram groups. High-frequency phonemes were more often audible with the EXP than with the other hearing aids for subjects with moderately and severely sloping audiograms. Output CVRs increased for some phonemes with a nonlinear hearing aid versus linear, but recognition of individual phonemes did not correlate significantly with CVR.

Female↗

PubMed1996

Evidence against the influence of aging on distortion-product otoacoustic emissions.

Previous research has reported reduced otoacoustic emission amplitude as a function of age. In each study, however, interpretation of findings was confounded by age-related hearing loss. The present study was designed to re-evaluate the contribution of age and peripheral hearing loss on the prevalence and amplitude of distortion-product otoacoustic emissions (DPOAEs) by controlling for degree of peripheral hearing loss. Twenty subjects were divided into four age ranges. All subjects in each group had 15 dB HL or better thresholds from 0.25 through 8 kHz and normal immittance findings. DPOAE audiograms recorded at three intensity levels and input/output functions recorded at six discrete frequencies showed no significant differences in amplitude or noise level between age groups. Findings indicate that when the degree of peripheral hearing loss is adequately controlled, there is no direct effect of advanced age on DPOAE measures. Clinical implications are discussed.

Acoustic Stimulation↗

PubMed1995

Stimulus intensity and fundamental frequency effects on duplex perception.

Duplex perception occurs when part of the acoustic signal is used for both a speech and a nonspeech percept. This phenomenon has been interpreted as evidence of a distinct system for speech perception that precedes other specialized systems of general auditory processing (such as auditory grouping, and perception of pitch, loudness, and timbre). This interpretation was investigated by using an intensity-dependent form of duplex perception with the acoustic pair /da/ and /ga/. The "base" portion of the stimulus, common to both, consisted of the first and second formants and the steady-state portion of the third formant (F3). The F3 transition (either a sinusoid or a true formant), which cued the difference between /da/ and /ga/, was varied in intensity and fundamental frequency (F0). For every subject, the level at which each type of F3 transition was barely audible in the context of the base, i.e., duplex perception threshold, was first established. Next, identification functions were obtained by varying the intensity of the F3 transition relative to each subject's duplex perception threshold. Results revealed that duplex perception thresholds decreased as the F0 of the F3 transition increasingly differed from the base. Also, identification functions showed that, as has been previously demonstrated, the F3 transition contributed to the speech percept over a wide range of intensities and fundamental frequencies. However, as F3 transition intensity increased well above duplex perception threshold, /ga/ identification decreased. Also, both /da/ and /ga/ identification progressively decreased as the F0 of the F3 transition increasingly differed from the base. Contrary to previous duplex perception reports, such findings indicate that both intensity and F0 information is available to the specialized speech perception system. Thus, the computations of the speech perception system and its relation to the general auditory processing systems need to be reexamined.

Adult↗

PubMed1991

A review of current "noise reduction" hearing aids: rationale, assumptions, and efficacy.

Amplification technology has changed considerably in the last decade, particularly with the introduction of more advanced adaptive signal processing approaches and digital/hybrid hearing aids. Because difficulty understanding speech in the presence of background noise is the most common complaint of hearing-impaired patients, an increasing number of these new products are being marketed as "noise reduction" hearing aids. There reamin, however, many unanswered questions regarding patient candidacy for these instruments, and the relative benefit that can be expected from the new technology. This article discusses issues and assumptions underlying noise reduction strategies, reviews categories of hearing aids on the market that are meant to alleviate listening difficulty in noise, and outlines future needs in research and development in this area.

Correction of Hearing Impairment↗

PubMed1990

Speech recognition in analog multichannel cochlear prostheses: initial experiments in controlling classifications.

Computer-synthesized vowels were used to examine methods for controlling and measuring the perceptions elicited during electrical stimulation of the human cochlea. In the first experiment, we measured the importance of the second formant (F2) in the identification of vowels, matched for duration, in a single subject with a multichannel cochlear implant. The subject never confused vowels having a "low" frequency F2 with those having a "high" frequency F2. In the second experiment, identification functions were generated for a series of vowels varying only in F2. When the pattern of F2 stimulation at the basilar membrane was manipulated, vowel identification functions were altered. For the categorization of vowels, the data indicate that the relative cochlear position of F2 stimulation was more important than fine-grain temporal waveform cues. The data are supportive of cochlear implant coding strategies that make use of cochlear place information. In the later experiments, we manipulated filter passbands and channel gains to explore their effect on these classifications. These preliminary studies indicate that it is possible to "fine-tune" such classifications.

Aged↗

PubMed1990

Functional reorganization of primary somatosensory cortex in adult owl monkeys after behaviorally controlled tactile stimulation.

1. Multiple microelectrode maps of the hand representation within and across the borders of cortical area 3b were obtained before, immediately after, or several weeks after a period of behaviorally controlled hand use. Owl monkeys were conditioned in a task that produced cutaneous stimulation of a limited sector of skin on the distal phalanges of one or more fingers. 2. Analysis of microelectrode mapping experiment data revealed that 1) stimulated skin surfaces were represented over expanded cortical areas. 2) Most of the cutaneous receptive fields recorded within these expanded cortical representational zones were unusually small. 3) The internal topography of representation of the stimulated and immediately surrounding skin surfaces differed greatly from that recorded in control experiments. Representational discontinuities emerged in this map region, and "hypercolumn" distances in this map sector were grossly abnormal. 4) Borders between the representations of individual digits and digit segments commonly shifted. 5) The functionally defined rostral border of area 3b shifted farther rostralward, manifesting either an expansion of the cutaneous area 3b fingertip representation into cortical field 3a or an emergence of a cutaneous input zone in the caudal aspect of this normally predominantly deep-receptor representational field. 6) Significant lateralward translocations of the borders between the representations of the hand and face were recorded in all cases. 7) The absolute locations--and in some cases the areas or magnifications--of representations of many skin surfaces not directly involved in the trained behavior also changed significantly. However, the most striking areal, positional, and topographic changes were related to the representations of the behaviorally stimulated skin in every studied monkey. 3. These experiments demonstrate that functional cortical remodeling of the S1 koniocortical field, area 3b, results from behavioral manipulations in normal adult owl monkeys. We hypothesize that these studies manifest operation of the basic adaptive cortical process(es) underlying cortical contributions to perception and learning.

Animals↗

PubMed1990

Revising the routine audiologic test battery to examine sources of interpatient variability.

The current audiologic test battery does not explain individual differences in performance in patients with similar degrees of sensorineural hearing loss. These patients can differ in perceived handicap and satisfaction with amplification, as well as in word-recognition ability in quiet and in noise. This article discusses several perceptual tasks that may reveal important interpatient differences. Each procedure is examined as a potential addition to the routine audiologic test battery in terms of three questions: does the procedure elicit novel information, are the results relevant to the speech perceptual process, and is the technique clinically practical?

Auditory Threshold↗

PubMed1989

Frequency discrimination ability and stop-consonant identification in normally hearing and hearing-impaired subjects.

Identification of place of articulation in the synthesized syllables /bi/, /di/, and /gi/ was examined in three groups of listeners: (a) normal hearers, (b) subjects with high-frequency sensorineural hearing loss, and (c) normally hearing subjects listening in noise. Stimuli with an appropriate second formant (F2) transition (moving-F2 stimuli) were compared with stimuli in which F2 was constant (straight-F2 stimuli) to examine the importance of the F2 transition in stop-consonant perception. For straight-F2 stimuli, burst spectrum and F2 frequency were appropriate for the syllable involved. Syllable duration also was a variable, with formant durations of 10, 19, 28, and 44 ms employed. All subjects' identification performance improved as stimulus duration increased. The groups were equivalent in terms of their identification of /di/ and /gi/ syllables, whereas the hearing-impaired and noise-masked normal listeners showed impaired performance for /bi/, particularly for the straight-F2 version. No difference in performance among groups was seen for /di/ and /gi/ stimuli for moving-F2 and straight-F2 versions. Second-formant frequency discrimination measures suggested that subjects' discrimination abilities were not acute enough to take advantage of the formant transition in the /di/ and /gi/ stimuli.

Adult↗