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Biomedical subjects

W J Keith

Publications and source records attributed to W J Keith.

7 recordsLinked to original sources
PubMed1991

Frequency-specific auditory brainstem responses relationship to behavioural thresholds in cochlear-impaired adults.

Auditory brainstem response (ABR) thresholds to ipsilaterally masked tone pip stimuli were obtained from three groups of hearing-impaired subjects. Using high-pass (for 500-Hz tone pips) and notched noise (for 1-, 2- and 4-kHz tone pips), ABR thresholds in subjects with low-frequency, high-frequency or flat cochlear hearing losses were compared to conventional pure-tone audiometric thresholds. A strong positive relationship was found between ABR and behavioural threshold elevation. Absolute ABR thresholds at 500 Hz were significantly higher than those at other frequencies. The results of this study indicate that frequency-specific ABR testing can provide an approximation of both degree and configuration of cochlear hearing losses in adults. Further refinements of testing and judging procedures are needed however to reduce the variation evident in our results and thus achieve the accuracy required for most clinical applications.

Adult↗
PubMed1989

Frequency-specific auditory brainstem responses. Effective masking levels and relationship to behavioural thresholds in normal hearing adults.

Ipsilateral masking levels and normal thresholds for tone pip auditory brainstem responses (ABRs) were investigated in normal subjects for the purpose of establishing recording parameters and norms for frequency-specific tone pip ABR testing. White noise was found to effectively mask ABRs to tone pips at mean signal-to-noise ratios of between -1 and -5.5 dB [dB peak-equivalent (pe) SPL/dB SPL] depending on the tone pip frequency. ABR thresholds were established for tone pips in the presence of ipsilateral masking with high-pass filtered noise for 50-Hz tone pips and notched noise for tone pips from 1,000 to 4,000 Hz, at a nominal signal-to-noise ratio of -5 dB (i.e. with the noise SPL measured prior to filtering). Thresholds occurred between 28.6 and 36.6 dB pe SPL, equivalent to 4.4-8.8 dB nHL. ABR thresholds for masked and unmasked tone pips did not differ significantly.

Adolescent↗
PubMed1988

Acoustic reflex amplitude and noise-induced hearing loss.

Acoustic reflex maximum amplitude measurements elicited both contralaterally and ipsilaterally were obtained from subjects with noise-induced hearing loss and compared with those obtained from normal-hearing subjects. The eliciting signal was a pure tone of 1 kHz presented for 1,000 ms. The groups were matched on age, sex, static immittance and ear canal volume. Acoustic reflex amplitudes were clearly reduced in noise-impaired subjects compared with normal-hearing subjects at a frequency where their hearing thresholds were normal.

Adult↗
PubMed1987

Effects of audiometric configuration on the auditory brain stem response.

Evidence reported in the literature indicates that wave I of the auditory brain stem response is influenced by cochlear contributions from a more basal area of the cochlea than is wave V. This phenomenon is invoked to explain different latency-intensity function patterns of waves I and V and the I-V interval for four types of cochlear hearing loss. In high frequency hearing losses wave V is delayed at low intensities. Wave I tends to be delayed at all intensities and by a greater amount than wave V. The I-V interval is often reduced with the effect maximal at higher intensities. Low frequency hearing losses tend to cause early wave V latencies at low intensities. Wave I latencies are normal. The I-V interval is therefore reduced at lower intensities. Flat hearing losses produce normal latency-intensity functions. High frequency notched audiograms are almost always associated with delayed wave V but early wave I latencies. The I-V interval is therefore significantly prolonged with the effect maximal at low intensities. The variability of the I-V interval as a function of audiometric configuration indicates that it is not a pure measure of central conduction time.

Adult↗
PubMed1978

Detection of hearing loss in infancy.

A neonatal hearing screening programme and a nine-month at risk hearing screening programme are analysed. Neither contributed significantly to the detection of deaf infants though nine month at risk screening can be worthwhile if well administered. Age of detection data for deaf pre-schoolers in New Zealand are presented. The responsibility of all professionals in contact with the infant population for early detection and referral of deaf infants is stressed.

Age Factors↗
PubMed1978

The effectiveness of two infant hearing screening programmes in New Zealand.

Early detection of congenital hearing loss is vital. A neonatal hearing screening programme and a 9 month at risk hearing screening programme are analysed. Neither contributed significantly to the detection of deaf infants, though 9 month at risk screening can be worthwhile if well administered. Age of detection data for deaf preschoolers in New Zealand are presented.

Age Factors↗