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Biomedical subjects

K E Hecox

Publications and source records attributed to K E Hecox.

At least 37 records · Page 2Linked to original sources
PubMed1990

Auditory nonlinearities measured with auditory-evoked potentials.

This article describes the use of auditory-evoked potentials (AEPs) as a tool to assess nonlinear processes in the auditory system. Two-tone signals were used as stimuli to obtain AEPs in both animal and human subjects. Frequency analysis of the physiologic waveforms revealed frequencies in the evoked potential that were not present in the acoustic signal. The largest distortion product in the evoked potential corresponded to the difference between the two primary frequencies (f2-f1). This distortion product was present in all subjects tested. Other distortion products at frequencies defined by n(f2-f1), where n less than 5, were also present in some individuals. These frequencies represent distortion components generated from an even-order nonlinear system. Extensive acoustic and electric calibration procedures provided substantial evidence that the distortion products recorded in the AEP were biologic in origin and not the result of acoustic or recording artifact.

Acoustic Stimulation↗
PubMed1990

A comparison of maximum length and Legendre sequences for the derivation of brain-stem auditory-evoked responses at rapid rates of stimulation.

Experiments were performed in which brain-stem auditory-evoked responses (BAERs) were elicited by two types of pseudorandom pulse trains: maximum length sequences (MLS) and Legendre sequences (LGS). In experiment 1, each pulse sequence was presented at 50 dB nHL with minimum pulse intervals varying from 1 to 10 ms. Wave V latency increased and wave V amplitude decreased with decreasing minimum pulse intervals, with no significant effect of the type of sequence (MLS vs LGS), and no significant interaction between sequence and minimum pulse interval in terms of wave V amplitude or latency. In a second experiment, the minimum pulse interval was held constant at 4 ms, while MLS and LGS levels were varied from 20 to 60 dB nHL. With increasing click intensity, there is a decrease in wave V latency and an increase in wave V amplitude. There was no significant effect of type of sequence (LGS vs MLS) or interaction between type of sequence and stimulus intensity for wave V amplitude or latency. Despite the obvious violation of the assumptions (linearity and stationarity) underlying the application of maximum length sequence analysis and Legendre sequence analysis, both techniques produced reliable responses remarkably similar in morphology to evoked responses obtained by conventional averaging. The results of these experiments support the possibility that analysis methods based on pseudorandom pulse sequences may prove more efficient in data collection and provide a more thorough description of the electrophysiologic behavior of the auditory system compared to conventional averaging.

Adult↗
PubMed1990

Brain-stem auditory-evoked responses elicited by maximum length sequences: effect of simultaneous masking noise.

The effects of masking noise on wave V of the brain-stem auditory-evoked response (BAER) obtained to pseudorandom pulse sequences are evaluated in two experiments. In the first experiment, the level of broadband noise was covaried with minimum pulse interval (rate) using maximum length sequence analysis (MLSA). Both increasing noise level and decreasing minimum pulse interval decrease wave V amplitude and increase wave V latency. A nonadditivity of rate and noise level was observed such that, at the shortest interpulse intervals, simultaneous background noise produced virtually no latency change and minimal amplitude change, for the noise levels tested. In a second experiment, high-pass masking was performed to assess the feasibility of derived-band techniques using maximum length sequence analysis (MLSA) and to compare the frequency regions responsible for the BAER using MLSA versus conventional averaging. Results of experiment 2 showed that reliable responses across high-pass masker cutoff frequency could be obtained in normal-hearing listeners. The frequency specificity of the MLSA-based responses was nearly identical to that obtained by conventional averaging, although both amplitude and latency of wave V were affected by the high-pass masker cutoff and minimum pulse interval values. These studies suggest that the neuronal populations and frequency regions responsible for the BAER are virtually the same for MLSA and conventional averaging.

Adult↗
PubMed1989

Variability of most comfortable and uncomfortable loudness levels to speech stimuli in the hearing impaired.

Methods for determining hearing aid settings often incorporate measurements of most comfortable loudness (MCL) and uncomfortable loudness (UCL) levels. This study examined the variability of loudness measures and their correlation to threshold data, using speech stimuli presented to hearing-impaired subjects. MCLs, UCLs, speech reception, and speech detection thresholds were obtained from 50 subjects having sensorineural impairments. The stimuli were CID W-2 spondees spoken by three female clinicians. Three MCLs and UCLs were obtained within each session, using ascending runs and a closed-set response list. Fifteen subjects were retested twice over intervals ranging from a week to several months. Between-session variability for the loudness measurements was less than or equal to 10 dB across sessions and speakers for the majority of subjects, with a tendency for the MCL and UCL to increase slightly over time. Significant variability was attributed to the use of live-voice presentation by different clinicians. High positive correlation was found between threshold and loudness data for subjects with relatively flat audiometric configurations but not for subjects demonstrating sharply sloping hearing losses.

Adult↗
PubMed1989

Effect of broadband noise on the human brain stem auditory evoked response.

The purpose of this paper is to describe the effect of broadband continuous noise on brain stem auditory evoked responses elicited from normal-hearing and hearing-impaired individuals. The motivation for this study derives from the increasing use of noise masking paradigms in diagnostic electrophysiology, the universal presence of background noise in everyday listening environments, and the frequent observation that background noise is more detrimental to the performance of the hearing-impaired individual than to the normal-hearing individual. Four studies were designed to evaluate: (1) the sensitivity and specificity of the latency-intensity series, (2) the sensitivity and specificity of the latency-noise series, (3) the dependence of the latency-noise series on signal-to-noise ratio near electrophysiologic threshold, and (4) the dependence of the latency-noise index on the signal level at which the test is performed. The results of the studies reported herein show that the electrophysiological response to increasing masker levels is more sensitive for identifying inner ear pathology than previously used latency-intensity series measures, without compromising specificity. It is suggested that simultaneous broadband masking should be considered as a test for localization of pathology in those subjects for whom routine behavioral measurements are not possible or when the results of such measurements are equivocal.

Adolescent↗
PubMed1989

Brain stem auditory evoked potentials in jaundiced Gunn rats.

Bilirubin encephalopathy causes potentially preventable brain damage and hearing loss. The site of auditory dysfunction is controversial, despite pathologic studies showing damage to brain stem auditory nuclei in humans and experimental animals. We studied the effects of bilirubin toxicity on the auditory system of homozygous jaundiced Gunn rats by use of brain stem auditory evoked potentials. Small but statistically significant abnormalities were found for wave latencies, interwave intervals, and amplitudes.

Animals↗
PubMed1989

Digital hearing aid technology: medical perspective.

This article provides a nontechnical introduction to digital hearing aids and the impact of digital signal processing on the delivery of hearing health care. Issues related to matching the patient's needs to signal processing solutions are covered, and specific recommendations with respect to criteria by which new hearing aid performance should be evaluated are discussed. The pivitol role played by medical personnel in initiating patient awareness of available options and in directing needs assessment is emphasized.

Correction of Hearing Impairment↗
PubMed1988

Development of brainstem auditory evoked potentials in heterozygous and homozygous jaundiced Gunn rats.

Bilirubin toxicity is a significant clinical problem causing neurologic and audiologic sequelae. To better understand the pathogenesis of bilirubin toxicity in the immature nervous system we studied the development of brainstem auditory evoked potentials (BAEPs) in jaundiced (jj) Gunn rats and their non-jaundiced (Jj) littermates. Littermate pairs of Jj and jj rats were studied serially from early infancy to adulthood. Replicated BAEPs to click stimuli at two different intensities (45 and 75 dB SPL) and rates (33 and 89/s) were obtained from animals anesthetized with ketamine and acepromazine and maintained at a constant rectal temperature. Jaundiced (jj) rats had increased latencies of waves II and III and the I-II and I-III intervals, and decreased amplitudes of waves II and III from 17 days of age through adulthood. For both groups, all latencies and interwave intervals decreased with age (P less than 0.0001 for each wave and interwave interval by repeated measures ANOVA), and the amplitude of II increased with age (P less than 0.0001). No group differences were found in wave I latency or amplitude, or in the latency change of waves I, II or III as a function of intensity (about 11 microseconds/dB at all ages), suggesting that peripheral auditory function is normal in jj rats. Finally, there were no different effects of stimulation rate on BAEP wave latencies between groups. The findings suggest dysfunction of the central (brainstem) auditory pathways at and rostral to the cochlear nuclei, and are consistent with studies showing destruction of the cochlear nuclei in this animal model and in humans with bilirubin toxicity. The central abnormalities previously found in adult, jaundiced rats are now demonstrated in animals as early as 17 days of age, when serum bilirubin concentration is maximum. The BAEP findings are similar to changes found in hyperbilirubinemic human neonates, and support the use of the Gunn rat animal model for the study of bilirubin encephalopathy.

Acoustic Stimulation↗
PubMed1988

The impact of digital technology on the selection and fitting of hearing aids.

The commercial availability of wearable digital hearing aids begins a new era in hearing aid technology. The impact of the introduction of digital technology extends from differences in hardware configuration to changes in the hearing aid fitting process to improvements in the perceptual experience enjoyed by the hearing-impaired individual. In this article, differences among analog, hybrid, and digital technology are reviewed. Performance differences among these technologies are examined in terms of flexibility, size, power consumption, programmability, and signal processing power. Emphasis is placed on the interdependence of hardware technology, signal processing algorithms, and the fitting procedure. The specific advantages of applying digital technology to fitting procedures are discussed. A number of perceptual and nonperceptual factors for the listener and the need to expand the history-taking process to identify performance-oriented patients are discussed. More rapid and reliable tests of patient preferences and speech intelligibility are needed for digital hearing aid fitting procedures.

Acoustics↗
PubMed1988

Language development: a sensory development and signal processing perspective.

The relationship between the development of sensory mechanisms and the maturation of language behavior is poorly understood. From the outset it is important to distinguish between what is necessary for the development of any language system versus what is involved in the development of the verbal language system in the unimpaired child. The presence of highly sophisticated language systems among persons who communicate manually reminds us that no single source of sensory information is absolutely required for the development of at least some form of language system. Nevertheless, there persists a general belief that the availability of an accurate representation of the acoustic environment will facilitate at least the normal process of language acquisition. A more tenable question is whether the completeness or accuracy of the sensory representation places limitations on the emergence of language comprehension and production. I think this is unlikely, unless the relatively untested area of the maturation of "nonlinear processing mechanisms" provides information different than that obtained from more traditional linear systems analysis approaches. The relative integrity of the language systems of the hearing impaired, despite very dramatic differences in auditory sensitivity and frequency-resolving power, argues strongly that whatever mechanisms account for language organization are relatively immune to significant alterations in sensory input. Caution must be exercised here, however, since these comments generally refer to the outcome of studies performed on persons with acquired hearing loss. Naturalistic or descriptive studies of patients with congenital hearing loss are always susceptible to the criticism that whatever agent or agents produced the sensory impairment may also have produced concomitant impairment of nonsensory mechanisms. Nevertheless, comparisons of young infants and hearing-impaired adults, with respect to behavioral studies, suggest that there is a sufficiently rich sensory representation of the acoustic environment to permit the development of language skills much earlier than they naturally emerge. Electrophysiologic comparisons of human newborns and adults also suggest that the diminished auditory sensitivity and alterations in the frequency contour of sensitivity are insufficient to explain age differences in language comprehension and production performance. It may well be that the brain mechanisms responsible for the establishment of language behavior are sufficiently flexible to accommodate even a greatly impoverished sensory representation.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain↗
PubMed1987

The effect of broadband noise on the human brain-stem auditory evoked response. III. Anatomic locus.

The effects of broadband noise on the brain-stem auditory evoked response (BAER) are reported for two experiments. Experiment 1 used a high-pass subtractive-masking technique and covaried derived bandwidth and continuous broadband noise level. Comparison of responses to half-octave wide derived bands in the presence of within-band noise showed that wave V latency changes were greater than could be explained on the basis of shifts in the cochlear region responsible for generating the response. The magnitude of within-band noise-induced wave V latency shift was independent of the frequency separation of the masker cutoffs. In experiment 2 the effects of noise level and rate on waves I, III, and V of the BAER were evaluated. Peak latencies increased and peak amplitudes decreased with increasing noise level and rate. Higher noise levels and rates produced an increased central (I-V) conduction time in which the wave III-V increase was greater than the wave I-III increase. Together, these results are most consistent with the hypothesis that a nonplace, central auditory mechanism produces most of the noise-induced latency shifts in normal-hearing adults.

Adult↗
PubMed1987

The effect of broadband noise on the human brain-stem auditory evoked response. IV. Additivity of forward-masking and rate-induced wave V latency shifts.

The additivity of forward masking and repetitive stimulation effects on wave V of the brain-stem auditory evoked response (BAER) was investigated. The effects of repetitive stimulation were evaluated for a stimulus train (called the adaptation series), with a 12.5-ms within-train interclick interval. The forward masker was a 100-ms, 80-dB SPL broadband noise with forward-masker intervals ranging from 12.5-87.5 ms. Forward masking and repetitive stimulation increased the latency of wave V of the BAER. The combined forward masking/adaptation series produced less wave V latency shift than the summed individual effects. Forward masking reduced wave V amplitude at brief forward masker intervals, while repetitive stimulation did not affect wave V amplitude. Wave V amplitude was decreased for the combined forward masking/adaptation series, and the time course of amplitude recovery of the combination was prolonged compared to the forward masking alone condition. The nonadditivity of forward masking and rate effects on wave V latency is similar to that found for repetitive stimulation and simultaneous masking [Burkard and Hecox, J. Acoust. Soc. Am. 74, 1204-1213 (1983)]. These findings are consistent with the position that forward masking and rate effects on wave V latency are produced by overlapping mechanisms.

Adult↗
PubMed1987

Speech distortion measures for hearing aids.

Advances in digital technology and the associated introduction of new forms of distortion led us to investigate supplementary measures of electroacoustic distortion for hearing aids. Mathematical techniques were used to formulate a working model in which the hearing aid acts as a time varying linear filter. This model embodies an approach to separating distortion into perceptually relevant and irrelevant categories. Digitized speech was converted to analog form, routed through a commercial hearing aid, and the output of the aid was redigitized and stored. For a given input signal, output speech waveforms were then compared to the model output and performance measures were derived. Distortion was plotted in three dimensions to permit interpretation with respect to time, frequency, and amplitude. These results provide a more comprehensive and general format for the analysis of hearing aid distortion.

Acoustics↗
PubMed1981

Prognostic importance of brainstem auditory evoked responses after asphyxia.

Brainstem auditory evoked responses were recorded after acute asphyxia in 126 infants, ages birth through 18 months. Of these, 21 had markedly abnormal amplitude ratios, and all infants with abnormal amplitude ratios had severe neurologic handicaps. An abnormal amplitude ratio predicts long-term neurologic sequelae of acute asphyxia in infants. Normal amplitude ratios did not, however, ensure normal neurologic outcome; 10 infants with normal responses were severely handicapped.

Asphyxia Neonatorum↗
PubMed1981

Brainstem auditory evoked response in the diagnosis of pediatric neurologic diseases.

Brainstem auditory evoked responses (BAERs) were measured in pediatric patients with neurologic diseases. Abnormalities of interwave intervals, amplitude ratios, and response to changing rate of stimulation were found in patients with tumors, myelin disorders, anoxic-ischemic encephalopathy, trauma, and neurodegenerative disorders. Reversibility of brainstem abnormalities (excluding multiple sclerosis) and sensitivity to toxic-metabolic disorders are features of the response not previously described in adults with neurologic disorders. The BAER is a promising new tool for the investigation of pediatric neurologic disease.

Adult↗
PubMed1978

Clinical applications of the auditory brain stem response.

The auditory brain stem response is a powerful new tool for the detection and quantification of hearing impairment, especially in the pediatric population. It gives exact information about the functional status of the cochlea and brain stem pathways. The technique distinguishes recruiting from nonrecruiting losses, predominantly high frequency from flat losses, and retrocochlear from peripheral disorders. The recent introduction of bone conducted stimuli should soon permit the unambiguous separation of conductive and sensorineural losses.

Adult↗