Randall C. Beattie’s research while affiliated with California State University, Long Beach and other places

This study was designed to compare normal-hearing and hearing-impaired auditory brainstem response (ABR) thresholds using 1 msec rise-plateau-fall times with ABR thresholds using two-cycle rise-fall limes and a one-cycle plateau. Because tone bursts of 500 Hz and 1000 Hz were selected for study, the respective two-cycle rise-fall times were 4 msec and 2 msec. This study also compared ABRs using repetition rates of 25.6/sec and 40/sec to determine if these two rates yield different ABR thresholds. Sixteen normal-hearing subjects and 13 subjects with mild-to-moderate sensorineural hearing loss participated in this study. The results revealed that increasing rise-fall time from 1 msec to 4 msec at 500 Hz, and from 1 msec to 2 msec at 1000 Hz, had little or no effect on the ABR threshold. Moreover, no differences in ABR thresholds were observed for the two repetition rates. Thus, these data suggest that differences in repetition rate do not account for the discrepancies in thresholds among studies. The prediction of pure-tone thresholds in dB HL from ABR thresholds in dB nHL was assessed using correction factor and regression procedures. Both methods yielded a reasonable approximation of the degree and configuration of hearing loss. Approximately 85% of pure-tone thresholds were predicted within ±10dB at 500 Hz and 1000 Hz. The present investigation suggests that either the 1 msec or 2-cycle rise-fall times maybe used for clinical purposes.

This study investigated the magnitude, reliability, and frequency of occurrence of peaks in the fine structure of the distortion product otoacoustic emission audiogram (DPOAE-gram). Thirty-six normal-hearing women were tested. Fine structure was assessed using 1/15 octave intervals (1000-8000 Hz) with primary tones presented at L1 = 65 and L2 = 55 dB SPL. DPOAE amplitudes were obtained at five frequencies (f2 = 1500 Hz, 2000 Hz, 3031 Hz, 4000 Hz, and 6031 Hz) for three values: one-frequency, three-frequency, and five-frequency averages. Compared to the one-frequency condition, averaging DPOAE amplitudes across three frequencies resulted in an improvement in reliability of approximately 1.0 dB. Because of the improved reliability, the three-frequency condition may be preferred when monitoring the effects of noise or ototoxic drugs. The number and reliability of amplitude peaks was ascertained. The reliability of the peak amplitudes (maxima or minima) was assessed with the standard deviation of test-retest differences. This value was 2.9 dB, suggesting that approximately 95% of measurements revealed test-retest differences within (+ or -) 5.9 dB. Thus, when obtaining measurements in 1/15 octave steps, it is common to observe maxima/minima in the DPOAE-gram of <6 dB that reflect test-retest variability. Moreover, due to chance, peaks greater than 6 dB will be observed in approximately 5% of measurements. Individual data points in the DPOAEgram may fall below normative values because of hearing loss, unreliability, or because of fine structure minima. Therefore, clinicians should conduct repeat testing and/or fine resolution measurements to ascertain whether the abnormal test results are due to cochlear impairment or normal variability.

This study compared auditory brainstem response (ABR) thresholds using linear versus Blackman gating functions for predicting pure tone thresholds in subjects with sensorineural hearing losses. Twenty-six subjects with gradually-to-steeply sloping hearing loss were tested with 500, 1000, 2000 and/or 4000 Hz tone bursts. The total stimulus durations were 3 msec for both gating functions. No statistically significant mean differences were found between ABR thresholds for the linear and Blackman tone bursts at any frequency. Linear regression equations were used to describe the relationship between ABR thresholds in dB nHL and pure tone thresholds in dB HL. Standard errors of estimate of about 11 dB were obtained at 500 and 1000 Hz for both tone bursts. At 2000 and 4000 Hz, standard errors of about 6 dB were observed for both the linear and Blackman tone bursts. These data suggest that 500 and 1000 Hz tone bursts can predict pure tone thresholds within 16 dB in approximately 85% of the cases, and that the 2000 and 4000 Hz tone bursts can predict pure tone thresholds within 9 dB in approximately 85% of the cases.

Because little information is available on the normal characteristics of input-output DPOAE functions, we measured (1) group slopes at f2 = 1000, 2000 and 4000 Hz for low-level (40-50 dB SPL), moderate-level (50-65 dB SPL), and high-level stimuli (65-75 dB SPL); (2) individual slopes for each frequency and intensity level segment; (3) test-retest reliability of slopes for each frequency and intensity level segment; and (4) the proportion of subjects with various input-output function shapes. Fifty normal-hearing female subjects were tested. The results showed that (1) the intersubject slope variability among subjects was large (standard deviations were ∼0.5); (2) the low-level segments exhibited steeper slopes (0.67-0.82) than the high-level segments (-0.03 -0.43), and the moderate-level segments showed intermediate slopes (0.39 - 0.64); and (3) slopes for the low-level and moderate-level segments tended to increase as frequency increased from 1000 Hz (slope = 0.53) to 4000 Hz (slope = 0.73). Approximately two thirds of the DPOAE input-output functions were the Linear-Plateau type (41%) or the Linear type (26%). The Rollover type of function also was fairly common and observed in 16% of the cases.

This Grason-Stadler GSI-60 system for measuring distortion product otoacoustic emissions (DPOAEs) allows the examiner to present one set of primary-tone pairs at a time (i.e., sequential presentation), or to present as many as four sets of primary-tone pairs at a time (i.e., simultaneous presentation). The Sequential and Simultaneous protocols were used to compare administration times, DPOAEs, and noise floors (NFs) on normal-hearing subjects at three frequencies (f2 = 1000, 2000, and 4000 Hz) and eight intensities (L1 = 40-75 dB SPL in 5 dB steps; L2 = 30-65 dB SPL). The Simultaneous protocol was completed in less than half the time (mean = 2 minutes, 21 seconds) required for the Sequential protocol (mean = 5 minutes, 13 seconds). When stimulus intensity (L1) was <60 dB SPL, the Sequential and Simultaneous protocols yielded similar DPOAEs and NFs. However, at the higher L1 intensities, the NFs for the Simultaneous protocol were larger than those for the Sequential protocol. The higher Simultaneous NFs reflect the greater system distortion/noise generated by the GSI-60 instrumentation. Reliability was assessed using the standard error of measurement of the difference between two scores. The data revealed no significant differences between protocols, and suggest that differences between two DPOAEs are statistically significant if they exceed approximately 7 dB (95% confidence interval).

This study assessed the test-retest reliability of distortion-product otoacoustic emissions (DPOAEs) at four frequencies (550, 1000, 2000 and 4000 Hz) over three time intervals. The time intervals were: (1) immediate test-retest reliability, in which the retest followed the test without any delay or repositioning of the probe tip; (2) very short-term test-retest reliability, in which the retest followed a 10-20-min break and involved removal and re-insertion of the probe tip; and (3) short-term test-retest reliability, in which the retest was conducted 5-10 days after the test. Fifty normal-hearing women were tested with a commercially available system for measuring DPOAEs (Grason-Stadler, GSI-60), which generated primary tones at 65 dB SPL (L1=L2). Standard errors of measurement at 550 Hz (approximately 4.6 dB) were nearly twice as large as those found for 1000 Hz, 2000 Hz, and 4000 Hz (approximately 2.5 dB). The short-term test-retest data suggest that there is a 95% probability that an individual's true DPOAE will fall within 5 dB of the obtained distortion product at 1000-4000 Hz and within 10 dB at 550 Hz. The standard error of measurement of the difference was calculated to assess whether two or more DPOAE measurements are significantly different (e.g. before versus after administration of an ototoxic drug or noise exposure). The data revealed that short-term differences (probe removed and subject retested on the same day or on different days) between two DPOAEs must exceed approximately 14 dB at 550 Hz and 7 dB at 1000-4000 Hz to be statistically significant at the 0.05 level of confidence.

This study assessed the test-retest reliability of distortion-product otoacoustic emissions (DPOAEs) at four frequencies (550, 1000, 2000 and 4000 Hz) over three time intervals. The time intervals were: (1) immediate test retest reliability, in which the retest followed the test without any delay or repositioning of the probe tip; (2) very short-term test-retest reliability, in which the retest followed a 10–20-min break and involved removal and re-insertion of the probe tip; and (3) short-term test-retest reliability, in which the retest was conducted 5–10 days after the test. Fifty normal-hearing women were tested with a commercially available system for measuring DPOAEs (Grason-Stadler, GSI-60), which generated primary tones at 65 dB SPL (L1=L2). Standard errors of measurement at 550 Hz (4.6 dB) were nearly twice as large as those found for 1000 Hz, 2000 Hz, and 4000 Hz (2.5 dB). The short-term test-retest data suggest that there is a 95% probability that an individual's true DPOAE will fall within 5 dB of the obtained distortion product at 1000–4000 Hz and within 10 dB at 550 Hz. The standard error of measurement of the difference was calculated to assess whether two or more DPOAE measurements are significantly different (e.g. before versus after administration of an ototoxic drug or noise exposure). The data revealed that short-term differences (probe removed and subject retested on the same day or on different days) between two DPOAEs must exceed approximately 14 dB at 550 Hz and 7 dB at 1000–1000 Hz to be statistically significant at the 0.05 level of confidence. Sumario Estc estudio evaluó la confiabilidad test-retest de las emisiones otoacústicas por productos de distorsión (DPOAE) en cuatro frecuencias (550, 1000, 2000 y 4000 Hz) y en tres intervalos de tiempo. Dichos intervalos fueron: (1) confiabilidad inmediata del test-retest, cuando el re-test siguió a la prueba inicial, sin demora y sin reposicionamiento de la sonda de prueba; (2) confiabilidad a muy corto plazo, donde el re-test se realizó después de una pausa de 10–20 minutos, e involucrando el retiro y la re-inserción de la sonda de prueba, y (3) confiabilidad a corto plazo, donde el re-test se llevó a cabo 5–10 días después de la prueba inicial. Se evaluaron cincuenta mujeres con audición normal utilizando un sistema de medición de DPOAE comercialmente disponible (Grason-Stadler, GSI-60), que generaba tonos primarios a 65 dB SPL (L1 =L2). Los errores estándar de medición a 550 Hz (4.6 dB) fueron de casi el doble de la magnitud de aquellos encontrados a 1000–4000 (2.5 dB). Los datos sobre la confiabilidad a corto plazo del test-retest sugieren que existe un 95% de probabilidad de que la verdadera DPOAE de un individuo sea encontrada en un rango de hasta 5 dB del producto de distorsión obtenido a 1000–4000 Hz y en un rango de hasta 10 dB a 550 Hz. El error estándar de medición de la difcrencia fue calculado para evaluar si dos o más mediciones de DPOAE eran significativamente diferentes (p.e. antes o después de la administratión de un medicamento ototóxico o de exposición al ruido). La información reveló que las diferencias a cortoplazo (remoción de la sonda de prueba y reevaluación del sujeto cl mismo día o en días diferentes) entre dos DPOAE deben sobrepasar aproximadamente 14 dB a 550 Hz y 7 dB a 1000–4000 Hz, para que sean estadisticamente significativas, en el nivel de confianza del 0.05.

Although tone-bursts have been commonly used in auditory brainstem response (ABR) evaluations for many years, national standards describing normal calibration values have not been established. This study was designed to gather normative threshold data to establish a physical reference for tone-burst stimuli that can be reproduced across clinics and laboratories. More specifically, we obtained norms for 3-msec tone-bursts presented at two repetition rates (9.3/sec and 39/sec), two gating functions (Trapezoid and Blackman), and four frequencies (500, 1000, 2000, and 4000 Hz). Our results are specified using three physical references: dB peak sound pressure level, dB peak-to-peak equivalent sound pressure level, and dB SPL (fast meter response, rate = 50 stimuli/sec). These data are offered for consideration when calibrating ABR equipment. The 39/sec stimulus rate yielded tone-burst thresholds that were approximately 3 dB lower than the 9.3/sec rate. The improvement in threshold with increasing stimulus rate may reflect the ability of the auditory system to integrate energy that occurs within a time interval of 200 to 500 msec (temporal integration). The Trapezoid gating function yielded thresholds that averaged 1.4 dB lower than the Blackman function. Although these differences are small and of little clinical importance, the cumulative effects of several instrument and/or procedural variables may yield clinically important differences. Abbreviations: ANSI = American National Standards Institute, IHS = Intelligent Hearing Systems, peSPL = peak equivalent sound pressure level, ppeSPL = peak-to-peak equivalent sound pressure level, pSPL = peak sound pressure level

This study investigated the effects of sample size on the test-retest reliability of the amplitude of distortion product otoacoustic emissions (DPOAE) (2f1-f2) and on the noise floor. Four pairs of primary frequencies (fl and f2) with geometric means of 531, 1000, 2000 and 4000 Hz were presented to 55 normal-hearing women at intensity levels of 35, 45 and 55 dB SPL (L1 = L2). Sample sizes of 12, 25, 50, 100, 200 and 400 sweeps were averaged. The results revealed that sample size, frequency, and intensity had little effect on the standard error of measurement. Thus, the DPOAE data were combined across all conditions and yielded a standard error of measurement of 2.2 dB. To assess whether two DPOAE measurements are statistically significant (e.g. before and after drug administration), the standard error of measurement of the difference between two values was calculated (3.1 dB). Thus, by use of the 95% confidence interval, the difference between two DPOAE is statistically significant if it exceeds approximately 6 dB.

This study investigated the effects of sample size on the noise floor and distortion product otoacoustic emissions (DPOAEs) in 55 normal-hearing subjects as a function of intensity. More specifically, we investigated the effects of sample size (12-400 sweeps) as a function of intensity (L1 = L2 = 35, 45 and 55 dB SPL), firstly, on the identifiability of DPOAEs (2F1-F2), secondly, on the noise floor adjacent to DPOAEs, and thirdly, on the magnitude of DPOAEs centred around geometric means of 531 Hz, 1,000 Hz, 2,000 Hz and 4,000 Hz. Testing was conducted with a commercially available system for measuring DPOAEs (Grason-Stadler, GSI-60). A constant F2:F1 ratio of 1.21 was used. As sample size increased from 12 to 400 sweeps, the noise floors decreased by about 13 dB; this closely corresponds to the expected 15 dB reduction based on the square root rule of noise reduction. The highest noise floors were measured at 531 Hz and the lowest noise floors at 2,000 Hz and 4,000 Hz. Identifiability increased as intensity increased from 35 to 55 dB SPL and as sample size increased from 12 to 400 sweeps for all stimulus conditions. Mean DPOAEs for all frequencies (531-4,000 Hz) appeared to decrease as sample size increased, particularly at stimulus levels of 35 dB and 45 dB SPL. These results may be explained by a reduction in the noise levels within the bandwidth of the DPOAE bin. That is, the DPOAE bin is comprised of the DPOAE plus background noise and these two quantities are not separated within the measured bin. Because the magnitude of bin containing DPOAEs is critically dependent on sample size, clinicians should carefully document this variable when collecting normative data. Similarly, clinicians who compare the magnitude of their DPOAEs to published data should note the sample size employed.