Biomedical subjects

David W Purcell

Publications and source records attributed to David W Purcell.

6 recordsLinked to original sources

PubMed2003

Concurrent measurement of distortion product otoacoustic emissions and auditory steady state evoked potentials.

Distortion product otoacoustic emissions (DPOAEs) and auditory steady state evoked response potentials (ASSRs) can both be evoked by tone pairs with frequencies f(1) and f(2). The DPOAE is maximal at 2f(1)-f(2) and the ASSR is maximal at f(2)-f(1). Since DPOAE magnitude depends on the ratio f(2)/f(1), but ASSR amplitude depends on the beat frequency f(2)-f(1), compromises are necessary when recording both responses concurrently. Tone pairs with f(2) of 900, 1800 and 3600 Hz were presented simultaneously at either 40 or 50 dB sound pressure level (SPL). The f(1) frequency of each pair was approximately 85 or 180 Hz lower than f(2). Phase measurements were used to calculate apparent latencies at 40 dB SPL. For increasing f(2), DPOAE latencies were 14.5, 9.7 and 6.3 ms for 85 Hz beats, and 11.5, 9.0 and 4.3 ms for 180 Hz beats. ASSR latencies were 22.0, 15.7 and 17.8 ms at 85 Hz, and 17.7, 11.3 and 9.6 ms at 180 Hz. From a model of the mechanical transmission in the cochlea, delays between the basilar membrane and the generator of the ASSR were estimated as 15.4, 12.2 and 15.3 ms at 85 Hz and 8.6, 7.6 and 8.0 ms at 180 Hz.

Acoustic Stimulation↗

PubMed2003

Sexual behavior among HIV-positive men who have sex with men: what's in a label?

Relatively little attention has been paid to the use and importance of labels used by men who have sex with men to describe insertive or receptive sexual behavior during intercourse. This study examines sexual self-labels, sexual behavior, HIV transmission risk, and psychological functioning among 205 HIV-seropositive men who have sex with men. The majority of participants (88%) identified as a top, a bottom, or versatile. Tops were more likely to engage in insertive anal intercourse than bottoms, and bottoms were more likely to engage in receptive anal intercourse than tops, with versatiles reporting intermediate rates of both behaviors. Although the results suggest preliminary evidence regarding the predictive utility of self-labels, sexual behaviors of self-label groups were greatly overlapping. Differences were found among self-label groups in gay self-identification, internalized homophobia, sexual sensation seeking, and anxiety. Results suggest an added value in assessing self-labels in addition to asking about sexual behavior.

Demography↗

PubMed2003

Estimating bone conduction transfer functions using otoacoustic emissions.

A technique for estimating the nonparametric bone conduction transfer function using distortion product otoacoustic emissions (DPOAEs) is presented. Individual transfer functions were obtained using DPOAEs recorded from a single ear of five normal-hearing adults. Repeatability of the technique was investigated by performing measurements on at least three dates. Functions were reasonably repeatable, and were unique to each individual as expected from subjective measurements. Input force and DPOAE measurements were made for each individual, and a model of the auditory periphery representative of an average person was employed. The technique is objective and requires only passive cooperation, but robust DPOAEs are needed and the measurement time can be onerous for a wide frequency band or fine frequency resolution. With appropriate adjustments to the model of the auditory periphery, the method could be applied with animal models.

Acoustics↗

PubMed2003

Human auditory steady-state responses: the effects of recording technique and state of arousal.

UNLABELLED: There is some controversy in the literature about whether auditory steady-state responses (ASSRs) can be reliably recorded in all subjects and whether these responses consistently decrease in amplitude during drowsiness. In 10 subjects, 40-Hz ASSRs became significantly different from background electroencephalogram activity with a probability of P < 0.01 and an average time of 22 s (range, 2-92 s), provided that the responses were analyzed with time-domain averaging rather than spectral averaging. In a second experiment with 10 subjects, 40-Hz ASSRs recorded between the vertex and posterior neck consistently decreased in amplitude during drowsiness and sleep. Findings that the ASSR may occasionally increase during drowsiness may be explained by postauricular muscle responses recorded from a mastoid reference. These may occur during drowsiness in association with rolling-eye movements. ASSRs recorded between the vertex and posterior neck are not distorted by these reflexes. These findings combine with previous literature on the effects of general anesthetics on the ASSR to confirm that the ASSR is a valid option for monitoring the hypnotic effects of general anesthetics. IMPLICATIONS: Auditory steady-state responses to stimuli presented at rates near 40 Hz can be used to monitor anesthesia. These responses can be quickly and reliably recorded during both sleep and wakefulness, provided that appropriate averaging techniques are used.

Acoustic Stimulation↗

PubMed2002

Estimating the audiogram using multiple auditory steady-state responses.

Multiple auditory steady-state responses were evoked by eight tonal stimuli (four per ear), with each stimulus simultaneously modulated in both amplitude and frequency. The modulation frequencies varied from 80 to 95 Hz and the carrier frequencies were 500, 1000, 2000, and 4000 Hz. For air conduction, the differences between physiologic thresholds for these mixed-modulation (MM) stimuli and behavioral thresholds for pure tones in 31 adult subjects with a sensorineural hearing impairment and 14 adult subjects with normal hearing were 14+/-11, 5+/-9, 5+/-9, and 9+/-10 dB (correlation coefficients .85, .94, .95, and .95) for the 500-, 1000-, 2000-, and 4000-Hz carrier frequencies, respectively. Similar results were obtained in subjects with simulated conductive hearing losses. Responses to stimuli presented through a forehead bone conductor showed physiologic-behavioral threshold differences of 22+/-8, 14+/-5, 5+/-8, and 5+/-10 dB for the 500-, 1000-, 2000-, and 4000-Hz carrier frequencies, respectively. These responses were attenuated by white noise presented concurrently through the bone conductor.

Adult↗

PubMed2002

Advantages and caveats when recording steady-state responses to multiple simultaneous stimuli.

This article considers the efficiency of evoked potential audiometry using steady-state responses evoked by multiple simultaneous stimuli with carrier frequencies at 500, 1000, 2000, and 4000 Hz. The general principles of signal-to-noise enhancement through averaging provide a basis for determining the time required to estimate thresholds. The advantage of the multiple-stimulus technique over a single-stimulus approach is less than the ratio of the number of stimuli presented. When testing two ears simultaneously, the advantage is typically that the multiple-stimulus technique is two to three times faster. One factor that increases the time of the multiple-response recording is the relatively small size of responses at 500 and 4000 Hz. Increasing the intensities of the 500- and 4000-Hz stimuli by 10 or 20 dB can enhance their responses without significantly changing the other responses. Using multiple simultaneous stimuli causes small changes in the responses compared with when the responses are evoked by single stimuli. The clearest of these interactions is the attenuation of the responses to low-frequency stimuli in the presence of higher-frequency stimuli. Although these interactions are interesting physiologically, their small size means that they do not lessen the advantages of the multiple-stimulus approach.

Audiometry, Pure-Tone↗