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Biomedical subjects

F P Harris

Publications and source records attributed to F P Harris.

26 records · Page 2Linked to original sources
PubMed1990

Distortion-product otoacoustic emissions in humans with high frequency sensorineural hearing loss.

Distortion-product otoacoustic emissions (DPOAEs) and pure-tone behavioral thresholds were compared in 20 ears with normal hearing and in 20 ears with high-frequency sensorineural hearing loss. The purpose was to determine if DPOAE amplitude is associated with pure-tone behavioral threshold. Comparison of results from the two groups of ears indicated that DPOAEs were reduced in amplitude or were absent in ears with high-frequency hearing loss. The differences occurred at frequencies above 1,500 Hz. Comparing results from 750 to 8,000 Hz within the same ear revealed a frequency-related correspondence of elevated behavioral threshold to reduced DPOAE amplitude. When behavioral thresholds were better than 20 dB HL, DPOAE amplitude was within the range (+/- 2 SDs) determined for the ears with normal hearing. When pure-tone threshold was greater than 50 dB HL, DPOAEs were absent or were significantly attenuated in 16/17 subjects (94%). The association of emission level with behavioral threshold level was variable when threshold was between these two extremes. Results imply that the measurement of DPOAEs has clinical potential as a means of detecting hearing loss by frequency.

Acoustics↗
PubMed1990

Psychoacoustical and ear canal cancellation of (2f1-f2)-distortion products.

Level and phase of the (2f1-f2)-difference tone were measured as a function of primary-tone level using the psychoacoustical method of cancellation and the objective method of emission cancellation for four frequency separations of f1 = 1620 Hz and f2 in four subjects. Differences between hearing- and emission-cancellation levels ranged from 60-33 dB as delta f = f2-f1 increased from 180 to 432 Hz. For smaller separations of the primaries, phase changes for emission cancellation covered a wide range and had sharp "steps," whereas for hearing cancellation, the phase varied only slightly. With wider separations of the primaries, the phase became more varied for hearing cancellation and more homogeneous for emission cancellation. Both emission- and hearing-cancellation level functions were nonmonotonic as a function of constant SL1 and varied SL2. Remarkable phase shifts always appeared near minima in level at all separations of the primaries for emission cancellation. Four sources may be contributing to the differences in results: (a) the frequency-dependent attenuation of the middle-ear transfer function, (b) the frequency-dependent mismatch of the acoustical impedances at the eardrum, (c) the frequency dependence of the microphone's sensitivity mounted within the probe, and (d) the different reaction of active nonlinear cochlear processes on the hearing- and emission-cancellation tones.

Adult↗
PubMed1990

Distortion product emissions in humans. II. Relations to acoustic immittance and stimulus frequency and spontaneous otoacoustic emissions in normally hearing subjects.

Multifrequency and multicomponent evaluations of aural acoustic immittance, including tympanometry and acoustic reflex testing, were performed on 44 normal ears to examine the influence of middle ear functioning on the generation and detection of distortion product otoacoustic emissions (DPEs). In the same ears, the prevalence and parametric features of spontaneous and stimulus frequency emissions were also assessed so that their relationship to the detection "thresholds" and amplitudes of corresponding DPEs could be determined. The general outcome was that none of the examined features of acoustic immittance provided an explanation for the discrete, low-amplitude DPE regions observed in about one third of normal ears. Moreover, the presence of typical spontaneous and stimulus frequency emissions in these same "irregular" ears indicated that emission generation and reverse cochlear transmission were also operating normally within these regions of reduced DPEs. Consequently, other, as yet undetermined influences appear to contribute to the DPE variability noted in some ears. Finally, the simultaneous presence of stimulus frequency emissions, but not spontaneous emissions, appeared to reduce the detection "thresholds" and increase the amplitudes of low-frequency DPEs.

Acoustic Impedance Tests↗
PubMed1990

Distortion product emissions in humans. I. Basic properties in normally hearing subjects.

Distortion product otoacoustic emissions (DPEs) at the 2f1-f2 frequency were recorded from 44 normal ears in response to equilevel primary tones. Detailed testing included the recording of DPE "audiograms" in 100-Hz steps from 1 to 8 kHz at three primary-tone levels (65, 75, and 85 dB sound pressure level [SPL]). In addition, response-growth or input-output (I/O) functions depicting the relationship of the amplitudes of DPEs to primary-tone levels, ranging from 25 to 85 dB SPL in 5-dB steps, were also tested for 11 frequencies distributed at quarter-octave intervals over the identical frequency range. The average DPE "audiogram" illustrating the frequency response of these emissions demonstrated a bilobed contour having a low-frequency maximum at approximately 1.5 kHz and a high-frequency peak that plateaued at about 5.5 kHz. The two maximum regions were separated by a minimum around 2.5 kHz. Depending on the frequency region, the average I/O functions exhibited detection "thresholds" at 3 dB above the noise floor at primary levels between 35 and 45 dB sound pressure level. The dynamic range of the emitted response between detection "threshold" and maximum amplitude varied over a 40-dB extent of the stimulus-level dimension. Approximately one third of the ears exhibited irregular DPE "audiograms" in which emitted responses were significantly reduced in restricted regions tested by low, medium, or high frequencies. When the 44 ears were separated into two groups representing more-normal and less-normal responses, the irregular "normal" ears demonstrated increased variability, especially in high-frequency regions. Mean age did not explain the differences noted between the two types of normally hearing subjects. However, across ears, DPE amplitudes and "thresholds" for the highest frequencies tested were correlated significantly with age in that the oldest individuals showed higher "thresholds" and lower amplitudes.

Acoustic Impedance Tests↗
PubMed1990

Distortion product emissions in humans. III. Influence of sensorineural hearing loss.

The realization that otoacoustic emissions are sensitive to cochlear disorders has resulted in the speculation that they may have considerable clinical potential as objective measures of hearing. To assess the clinical utility of one type of emission, the distortion product emission (DPE), a study was undertaken in individuals with hearing impairments representing a number of common otologic disorders. The results of this investigation provided evidence that tests of DPEs promise to satisfy a number of requirements important to clinical testing, including objectivity of measurement procedures, test-retest reliability, simple subject preparation, readily available instrumentation, and relatively brief examination periods. The fine resolution of DPEs within the stimulus frequency and level domains also permits an accurate confirmation of the pattern of hearing loss. For example, tests of DPEs detected a 20-dB hearing level impairment at a single frequency in an ear exhibiting early signs of noise-induced hearing loss, and a 10-dB improvement in sensitivity following ingestion of the hyperosmotic agent glycerol in an ear displaying a mild to moderate hearing loss due to Meniere's disease. Finally, the application of DPEs to the objective testing of otologic disorders suggests that the ability of these responses to assess the sensory component of a sensorineural disorder may contribute to the eventual understanding of the complicated pathogenesis of many cochlear diseases. When all the positive features of DPE testing are realized, the potential contribution that these measures can make in a clinical setting becomes apparent.

Adult↗
PubMed1989

Acoustic distortion products in humans: systematic changes in amplitudes as a function of f2/f1 ratio.

The effects of primary-tone separation on the amplitude of distortion-product emissions (DPEs) at the 2f1-f2 frequency were systematically examined in ten ears of five subjects. All individuals had normal hearing and middle-ear function based upon standard clinical measures. Acoustic-distortion products were elicited at 1, 2.5, and 4 kHz by equilevel primaries at 65, 75, and 85 dB SPL, while f2/f1 ratios were varied in 0.02 increments from 1.01-1.41 (4 kHz), 1.01-1.59 (2.5 kHz), or 1.01-1.79 (1 kHz). A principal outcome reflected in the detailed structure of both average and individual ratio functions was a nonmonotonic change in DPE amplitude as the ratio of f2/f1 increased. Despite the presence of amplitude nonmonotonicities, there was clearly a region of f1 and f2 separation that generated a maximum DPE. The effects of primary-tone separation on DPE amplitudes were systematically related to DPE frequency and primary-tone level. For all three levels of stimulation, the f2/f1 ratio was inversely related to DPE frequency. Thus larger ratios reflecting a greater separation of f1 and f2 were more effective in generating DPEs at 1 kHz rather than at 4 kHz. The optimal ratio for 2.5 kHz fell at an intermediate value. Conversely, acoustic distortion-product amplitude as a function of primary-tone level was directly related to the frequency separation of the primary tones. Regardless of the frequency region of the primary tones, smaller f2/f1 ratios were superior in generating DPEs in response to 65-dB stimuli, whereas larger ratios elicited bigger DPEs with primaries at 75 and 85 dB SPL. Within any specific stimulus-parameter combination, individual variability in DPE amplitude was noted. When all stimulus conditions describing the variations in frequency and level were considered, an f2/f1 ratio of 1.22 was most effective in maximizing DPE amplitude.

Adult↗
PubMedDate not supplied

Repeatability of distortion product otoacoustic emissions in normally hearing humans.

Distortion product otoacoustic emissions (DPOAEs) at the frequency of 2f1-f2 were measured in one or both ears of 12 young adults during 4 test sessions over a 6-week period. The purpose was to determine the variability in DPOAE amplitudes and 'detection thresholds' over repeated measurements using a computer-based time-averaging system. DPOAEs were generated with f1 and f2 relative to (f1f2)1/2 in two basic paradigms: (a) fixed levels of L1 = L2 of 70 and 55 dB SPL over a stimulus range from 0.8 to 8 kHz in 0.2-octave intervals; (b) input-output functions in stimulus regions of 0.8, 1, 1.5, 2, 3, 4 and 6 kHz, L1 from 35 to 70 dB SPL changing in 5-dB steps and L2 at 6 dB below the amplitude of L1. The mean variability of DPOAE amplitudes with equilevel stimuli was 1.8 dB (SD = 1.8) for L1 = 70 dB SPL and 2.9 dB (SD = 2.7) for L1 = 55 dB SPL. It was 1.7 dB (SD = 1.7) and 2.4 dB (SD = 2.0) for comparable levels of L1 with L2 at 6 dB below L1. Variability in amplitude of the DPOAEs for the fixed-level condition was greatest overall above 6 kHz and below 1 kHz and in the 2-kHz region for one third of the subjects. Neither individual differences in emission amplitudes nor the presence of spontaneous otoacoustic emissions had a significant influence on the amount of amplitude variability within ears. Variability was not influenced by the length of time between measurements from 1 to 6 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗