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Biomedical subjects

Tiffany A Johnson

Publications and source records attributed to Tiffany A Johnson.

10 recordsLinked to original sources
PubMed2006

Using a combination of click- and tone burst-evoked auditory brain stem response measurements to estimate pure-tone thresholds.

DESIGN: A retrospective medical record review of evoked potential and audiometric data were used to determine the accuracy with which click-evoked and tone burst-evoked auditory brain stem response (ABR) thresholds predict pure-tone audiometric thresholds. METHODS: The medical records were reviewed of a consecutive group of patients who were referred for ABR testing for audiometric purposes over the past 4 yrs. ABR thresholds were measured for clicks and for several tone bursts, including a single-cycle, Blackman-windowed, 250-Hz tone burst, which has a broad spectrum with little energy above 600 Hz. Typically, the ABR data were collected because the patients were unable to provide reliable estimates of hearing sensitivity, based on behavioral test techniques, due to developmental level. Data were included only if subsequently obtained behavioral audiometric data were available to which the ABR data could be compared. Almost invariably, the behavioral data were collected after the ABR results were obtained. Because of this, data were included on only those ears for which middle ear tests (tympanometry, otoscopic examination, pure-tone air- and bone-conduction thresholds) indicated that middle ear status was similar at the times of both tests. With these inclusion criteria, data were available on 140 ears of 77 subjects. RESULTS: Correlation was 0.94 between click-evoked ABR thresholds and the average pure-tone threshold at 2 and 4 kHz. Correlations exceeded 0.92 between ABR thresholds for the 250-Hz tone burst and low-frequency behavioral thresholds (250 Hz, 500 Hz, and the average pure-tone thresholds at 250 and 500 Hz). Similar or higher correlations were observed when ABR thresholds at other frequencies were compared with the pure-tone thresholds at corresponding frequencies. Differences between ABR and behavioral threshold depended on behavioral threshold, with ABR thresholds overestimating behavioral threshold in cases of normal hearing and underestimating behavioral threshold in cases of hearing loss. CONCLUSIONS: These results suggest that ABR thresholds can be used to predict pure-tone behavioral thresholds for a wide range of frequencies. Although controversial, the data reviewed in this paper suggest that click-evoked ABR thresholds result in reasonable predictions of the average behavioral thresholds at 2 and 4 kHz. However, there were cases for which click-evoked ABR thresholds underestimated hearing loss at these frequencies. There are several other reasons why click-evoked ABR measurements were made, including that they (1) generally result in well-formed responses, (2) assist in determining whether auditory neuropathy exists, and (3) can be obtained in a relatively brief amount of time. Low-frequency thresholds were predicted well by ABR thresholds to a single-cycle, 250-Hz tone burst. In combination, click-evoked and low-frequency tone burst-evoked ABR threshold measurements might be used to quickly provide important clinical information for both ends of the audiogram. These measurements could be supplemented by ABR threshold measurements at other frequencies, if time permits. However, it may be possible to plan initial intervention strategies based on data for these two stimuli.

Acoustic Stimulation↗
PubMed2006

Influence of primary-level and primary-frequency ratios on human distortion product otoacoustic emissions.

The combined influence of primary-level differences (L1-L2) and primary-frequency ratio (f2/f1) on distortion product otoacoustic emission (DPOAE) level was investigated in 20 normal-hearing subjects. DPOAEs were recorded with continuously varying stimulus levels [Neely et al. J. Acoust. Soc. Am. 117, 1248-1259 (2005)] for the following stimulus conditions: f2= 1, 2, 4, and 8 kHz and f2/f1=1.05 to 1.4; various L1-L2, including one individually optimized to produce the largest DPOAE. For broadly spaced primary frequencies at low L2 levels, the largest DPOAEs were recorded when L1 was much higher than L2, with L1 remaining relatively constant as L2 increased. As f2/fl decreased, the largest DPOAEs were observed when L1 was closer to L2 and increased as L2 increased. Optimal values for L1-L2 and f2 f1 were derived from these data. In general, average DPOAE levels for the new L1-L2 and f2/f1 were equivalent to or larger than those observed for other stimulus combinations, including the L1-L2 described by Kummer et al. [J. Acoust. Soc. Am. 103, 3431-3444 (1998)] and those defined by Neely et al. in which L1-L2 was evaluated, but f2/f1 was fixed at 1.2.

Acoustic Stimulation↗
PubMed2006

Reducing reflected contributions to ear-canal distortion product otoacoustic emissions in humans.

Distortion product otoacoustic emission (DPOAE) fine structure has been attributed to the interaction of two cochlear-source mechanisms (distortion and reflection sources). A suppressor presented near the 2f1-f2 frequency reduces the reflection-source contribution and, therefore, DPOAE fine structure. Optimal relationships between stimulus and suppressor conditions, however, have not been described. In this study, the relationship between suppressor level (L3) and stimulus level (L2) was evaluated to determine the L3 that was most effective at reducing fine structure. Subjects were initially screened to find individuals who produced DPOAE fine structure. A difference in the prevalence of fine structure in two frequency intervals was observed. At 2 kHz, 11 of 12 subjects exhibited fine structure, as compared to 5 of 22 subjects at 4 kHz. Only subjects demonstrating fine structure participated in subsequent measurements. DPOAE responses were evaluated in 1/3-octave intervals centered at 2 or 4 kHz, with 4 subjects contributing data at each interval. Multiple L3's were evaluated for each L2, which ranged from 20 to 80 dB SPL. The results indicated that one or more L3's at each L2 were roughly equally effective at reducing DPOAE fine structure. However, no single L3 was effective at all L2's in every subject.

Acoustic Stimulation↗
PubMed2005

Threshold prediction using the auditory steady-state response and the tone burst auditory brain stem response: a within-subject comparison.

OBJECTIVE: The purpose of this study was to evaluate the accuracy with which auditory steady-state response (ASSR) and tone burst auditory brain stem response (ABR) thresholds predict behavioral thresholds, using a within-subjects design. Because the spectra of the stimuli used to evoke the ABR and the ASSR differ, it was hypothesized that the predictive accuracy also would differ, particularly in subjects with steeply sloping hearing losses. DESIGN: ASSR and ABR thresholds were recorded in a group of 14 adults with normal hearing, 10 adults with flat, sensorineural hearing losses, and 10 adults with steeply sloping, high-frequency, sensorineural hearing losses. Evoked-potential thresholds were recorded at 1, 1.5, and 2 kHz and were compared with behavioral, pure-tone thresholds. The predictive accuracy of two ABR protocols was evaluated: Blackman-gated tone bursts and linear-gated tone bursts presented in a background of notched noise. Two ASSR stimulation protocols also were evaluated: 100% amplitude-modulated (AM) sinusoids and 100% AM plus 25% frequency-modulated (FM) sinusoids. RESULTS: The results suggested there was no difference in the accuracy with which either ABR protocol predicted behavioral threshold, nor was there any difference in the predictive accuracy of the two ASSR protocols. On average, ABR thresholds were recorded 3 dB closer to behavioral threshold than ASSR thresholds. However, in the subjects with the most steeply sloping hearing losses, ABR thresholds were recorded as much as 25 dB below behavioral threshold, whereas ASSR thresholds were never recorded more than 5 dB below behavioral threshold, which may reflect more spread of excitation for the ABR than for the ASSR. In contrast, the ASSR overestimated behavioral threshold in two subjects with normal hearing, where the ABR provided a more accurate prediction of behavioral threshold. CONCLUSIONS: Both the ABR and the ASSR provided reasonably accurate predictions of behavioral threshold across the three subject groups. There was no evidence that the predictive accuracy of the ABR evoked using Blackman-gated tone bursts differed from the predictive accuracy observed when linear-gated tone bursts were presented in conjunction with notched noise. Similarly, there was no evidence that the predictive accuracy of the AM ASSR differed from the AM/FM ASSR. In general, ABR thresholds were recorded at levels closer to behavioral threshold than the ASSR. For certain individuals with steeply sloping hearing losses, the ASSR may be a more accurate predictor of behavioral thresholds; however, the ABR may be a more appropriate choice when predicting behavioral thresholds in a population where the incidence of normal hearing is expected to be high.

Acoustic Stimulation↗
PubMed2005

A validation and potential clinical application of multivariate analyses of distortion-product otoacoustic emission data.

OBJECTIVE: To test the generalizability of multivariate analyses of distortion-product otoacoustic emission (DPOAE) data. Previously published multivariate solutions were applied to a new set of data to determine if test-performance improvements, evident in previous reports, are retained. An additional objective was to provide an alternative approach for making multivariate dichotomous decisions of hearing status in the clinic, based on DPOAE measurements. DESIGN: DPOAE level and noise were obtained in 345 ears of 187 subjects. Approximately one third of the subjects had normal hearing, whereas the remainder had hearing loss, ranging from 25 to more than 120 dB HL. DPOAE data were collected at each of nine frequencies. After data collection, clinical decision theory, in combination with univariate (DPOAE level and signal-to-noise ratio [SNR]) and multivariate (logistic regression) analyses, was used to construct relative operating characteristic (ROC) curves and to generate ROC curve areas. In addition, test performance was assessed by fixing the false-alarm rate and comparing different approaches to analyses in terms of their failure rates as a function of magnitude of hearing loss. The DPOAE test results were compared with either single-frequency or multifrequency gold standards. The multivariate solutions were taken from previously published work (Dorn et al., 1999; Gorga, et al., 1999). RESULTS: DPOAE level and SNR resulted in roughly equivalent test performance (ROC curve areas and failure rates among ears with hearing loss), although DPOAE level performed better for frequencies above 1 kHz, and SNR performed better for frequencies at 0.75 and 1 kHz. Multivariate analyses resulted in better test performance for nearly all conditions, compared with the univariate approaches that used either DPOAE level or SNR. The improvements in test performance were greatest for the frequencies at which the univariate analyses performed poorest (0.75 kHz, 1 kHz, and 8 kHz). Less difference was observed between univariate and multivariate approaches when multifrequency gold standards were used; however, even for the multifrequency cases, multivariate analyses generally resulted in better performance. An approach that might facilitate the interpretation of multifrequency DPOAE measurements in the clinic is described. CONCLUSIONS: Previously described multivariate analyses were robust in that they improved test performance when applied to an entirely new set of DPOAE data. This, in turn, suggests that the previously described multivariate solutions may have clinical utility in that they are expected to improve test performance at no additional cost in terms of data-acquisition or data-analysis time. In addition to demonstrating that these solutions generalized to new data, an alternative approach to interpreting multifrequency DPOAE measurements is provided that includes the advantages of using multivariate analyses. This new metric may be useful when DPOAEs are used for screening purposes.

Adolescent↗
PubMed2005

Distortion-product otoacoustic emission measured with continuously varying stimulus level.

Distortion-product otoacoustic emissions (DPOAE) are measured by stimulating the ear with two simultaneous tones. A novel method for measuring DPOAEs has been developed in which the tone levels vary continuously instead of in discrete steps. Varying the tone levels continuously may offer advantages for characterizing DPOAE level as a function of stimulus level. For equivalent primary levels, DPOAE levels measured with the continuous-level method were the same as levels obtained with the discrete-level method, thus validating the new method. Continuous-level measurements were used to determine the optimal L1 for each L2 in individual subjects (N= 20) at f2 = 1, 2, 4, and 8 kHz by using a Lissajous path that covered a wide range of stimulus levels. The optimal L1 (defined as the L1 that resulted in the largest DPOAE for each L2) varied across subjects and across frequency. The optimal difference between L1 and L2 decreased with increasing L2 at all frequencies, and increased with frequency when L2 was low. When the optimal L1 was determined individually for each ear, the DPOAE levels were larger and less variable than those obtained using the equation for L1 suggested by Kummer et al. [J. Acoust. Soc. Am. 103, 3431-3444 (1998)].

Acoustic Stimulation↗
PubMed2005

Stimulus-frequency otoacoustic emissions measured with amplitude-modulated suppressor tones (L).

Stimulus-frequency otoacoustic emissions (SFOAEs) are typically derived as the difference in sound pressure in the ear canal with and without a suppressor tone added to the probe tone. A novel variation of this method applies a sinusoidal amplitude modulation (AM) to the suppressor tone, which causes the SFOAE to also be modulated. The AM-SFOAE can be separated from the probe frequency using spectral methods. AM-SFOAE measurements are described for four normal-hearing subjects using 6-Hz AM. Because the suppressor modulation is at a higher rate, the AM-SFOAE technique avoids the confounding influence of heartbeat, which also modulates the probe tone.

Acoustic Stimulation↗
PubMed2004

Estimating air-bone gaps using auditory steady-state responses.

Auditory steady-state responses (ASSR) were recorded using stimuli presented both via air conduction (AC ASSR) and bone conduction (BC ASSR) in 10 normal-hearing subjects with different degrees of simulated conductive hearing losses. The ASSR-estimated ABG (air-bone gap) was compared with the ABG measured using traditional pure-tone audiometric procedures. Reproducibility of the BC ASSR electrophysiological thresholds was also assessed. Additionally, a group of five subjects with profound sensorineural hearing loss was used to establish stimulation levels in which the BC ASSR was contaminated by stimulus artifact. Results of this investigation showed that the ASSR and behavioral ABGs were strongly correlated with each other (r = .81). However, ASSR-estimated ABGs slightly overestimated the magnitude of the behavioral. Reproducibility of the BC ASSR electrophysiological thresholds was good. Data from the five subjects with profound hearing loss, however, demonstrated that the levels where stimulus artifact became problematic were relatively low. This means BC stimulation may be appropriate only for subjects with normal or mildly impaired cochlear sensitivity.

Adult↗
PubMed2003

Impact of digital labeling on outcome measures.

OBJECTIVE: The purpose of this study was to determine whether the label attached to the hearing aid being presented would bias outcome measures towards newer technological designs. DESIGN: Two groups of subjects participated in this investigation. The groups were matched for age, gender, previous hearing aid experience, degree and configuration of hearing loss. Group A wore each of two digital hearing aids for 1 mo; Group B wore the same digital hearing aid for 2 mo, but the subjects were given the impression they were changing hearing aids after 1 mo. In each group the subjects were told that one of the months they were wearing a "digital" hearing aid and one of the months they were wearing a "conventional" hearing aid. Outcome measures consisted of a number of behavioral speech perception tasks and self-report measures, each completed at the onset and after 1 mo use with the hearing aids. RESULTS: Labeling effects were observed for many of the outcome measures. Using a mixed-model factorial analysis of variance to control for irrelevant variables and to explore interaction terms, prejudice (digital versus conventional labeling) was treated as a within-subject factor while the subject group (A or B) and clinician were treated as between-subject factors. Although only the APHAB RV and BN scales showed significant labeling effects on their own, the group of tests used in this study showed a significant labeling effect as a whole (p < 0.01). The total influence of labeling and related interaction terms indicated labeling-related effects accounted for 2 to 32% of the variance in individual outcome measures. DISCUSSION: The results of this investigation indicate a need for double-blinding in hearing aid research aimed at assessing the effectiveness of newer technologies, as well as a need for clinicians to critically evaluate the research describing the potential advantages of certain circuit options.

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