PP1610 - Achieving the Lowest and Most Stable Ultra-High-Frequency Thresholds

Abstract:
Ultra-high frequency hearing sensitivity may be helpful in ototoxic monitoring or tinnitus assessment. Impacts of circumaural headphone position and stimulus type on ultra-high frequency thresholds and variability were investigated. Thresholds at 12.5k and 16 kHz for warbled and pulsed pure-tone stimuli were obtained from seven participants using DD-450 circumaural headphones across two sessions. During each session, thresholds were obtained in three concha-relative headphone positions (forward, backward, and standard concha-centered). Overall, warbled stimulus yielded the best performance (lowest thresholds and test re-test variability). The best headphone position varied depending on the frequency and whether the lowest or most stable thresholds were targeted.

Summary:
Ultra-high frequency audiometric evaluations are essential in tinnitus assessment and monitoring (Vielsmeier et al., 2015) as well as ototoxicity monitoring (Valiente et al., 2016). The current project investigated which stimulus type and circumaural headphone placement yield the most stable and lowest ultra-high frequency thresholds. Pulsed pure-tone, FRESH noise, steady pure-tone, and warbled-pure-tone stimuli were initially considered. FRESH noise was removed from consideration due to equipment limitations (FRESH noise was only available up to 12.5 kHz). In previous studies, steady pure tones were more difficult when compared to pulsed and warbled pure tones (Lentz et al., 2017). Warbled stimuli yield lower thresholds in ultra-high frequency audiometry (Hamill & Haas, 1986; Lentz et al., 2017). However, pulsed pure tones have been recommended due to reduced listening difficulty and elimination of off-frequency listening identified with the use of other stimuli, including warbled pure tones (Lentz et al., 2017). Transducer placement can affect ultra-high frequency thresholds due to high-frequency directionality (Borchgrevink et al., 1996). At 6000 and 8000 Hz, as much as a 5 to 40 dB threshold improvement based on headphone position has been identified (Flottorp, 2009). The purpose of this study was to determine how circumaural headphone position relative to the concha, utilizing warbled and pulsed pure tones, affects ultra-high frequency threshold stability and minimum threshold levels.

Methods:

Pilot Study:
A pilot study investigated whether pulsed, steady, or warbled pure tones produce the most stable and lowest thresholds in three headphone positions (forward, backward, and standard concha-centered, always with the pinna within the padding of the headphone), at 4, 8, 10, 12.5 and 16 kHz. The participants were two audiologists and two audiology externs. As suggested by descriptive statistics, pulsed and warbled pure tones produced the lowest and most stable thresholds and were therefore used for the current research.

Full Study:

Subjects:
Five audiologists and two audiology externs.

Measurements:
Threshold search at 12.5k and 16 kHz using DD-450 circumaural headphones was completed six times for each ear during each data collection session. Pulsed and warbled pure tones were used in each headphone location. Two data collection sessions, separated by a minimum of four hours, were completed by each participant. Due to the limited number of participants, chi-square analyses were conducted to determine which stimulus type and headphone location yielded the lowest thresholds at ultra-high frequencies with the least variability.

Results:
Warbled pure-tone stimulus trended towards yielding the lowest thresholds and variability as compared to the pulsed pure-tone stimulus. However, the average effects were small ( < 4 dB). The average effects of headphone position were also small overall. However, in individual cases, threshold magnitude and variability could be clinically significant as test re-test variation was sometimes greater than 10 dB, most frequently when the headphones were in the backward position.

Conclusions:
Warbled pure-tone stimuli are favored when conducting ultra-high frequency audiometry with circumaural headphones. The cost of potential off-frequency hearing appears well offset by response stability. Accurate headphone placement is important for ultra-high frequency test accuracy.