Phenomenologic aspects of the acoustic reflex following noise exposure.

Thirty-seven normal hearing subjects were exposed to broadband noise for 2 hours at 90 dB (Lp). Measures of behavioral thresholds and acoustic reflex activity were completed prior to and following the noise exposure. As expected, temporary threshold shift was obtained at several different frequencies (1.0-6.0 kHz). In addition, reflex threshold shift occurred for all pure-tone elicitors under evaluation (0.5 to 4.0 kHz). The observed shift in acoustic reflex threshold at 0.5 kHz without a concomitant change in behavioral sensitivity reveals the limitation of utilizing behavioral threshold testing as the sole measure of cochlear disruption. Changes in acoustic reflex onset latency and magnitude were not observed after compensating for shifts in acoustic reflex threshold.

Ear canal volume and variability in the patterns of temporary threshold shifts.

Ear canal resonance is thought to be responsible for the prominent loss of hearing in the 3.0 to 6.0 kHz region caused by over-exposure to noise. Relationships were identified between frequency-of-maximum temporary threshold shift (TTS) and physical measurements of the ear canal in 56 subjects. TTSs were produced by two separate exposures to broadband noise of either 2 hr or 20 minute duration. Ear canal volume was estimated from admittance tympanograms, diameter of the canal opening was measured, and canal length was calculated. Thirty subjects suffered the greatest TTS at 4.0 kHz, while 17 and 9 subjects had the greatest shift at 3.0 and 6.0 kHz, respectively. With subjects grouped according to frequency-of-maximum TTS, mean ear canal volume was found to be significantly different. Subjects with larger volumes were more likely to suffer the greatest loss at 3.0 kHz. Accordingly, subjects with smaller ear canal volumes suffered peak hearing loss at 6.0 kHz. Significant correlations were identified between ear canal volume and calculated length (resonance). Also, modest correlations were noted between frequency-of-maximum TTS and volume as well as TTS and length.

Self-report approach to assessing benefit derived from amplification.

The ultimate goal of hearing aid selection procedures is successful use of amplification in everyday communication. The need to validate selection procedures is widely recognized, but the development of relevant criterion measures is a prerequisite to evaluation of predictive validity. This study explored the feasibility of using a self-report method of measuring success with amplification. A 64-item questionnaire was administered to 128 experienced hearing aid users who rated the benefit received from amplification in a variety of situations. Internal consistency reliability was excellent (alpha = .96), indicating that the perceived benefit is sufficiently consistent across situations to yield reliable measures of individual differences among patients. Factor analysis of the interitem correlation matrix, however, led to the identification of four types of situations that might be assessed separately: (a) noisy situations; (b) quiet situations with the speaker in proximity; (c) situations with reduced signal information; and (d) situations with nonspeech stimuli. In general, patients reported significantly more benefit from their aids in quiet situations than in noise. A self-report methodology for measuring successful use of amplification in daily life appears promising as a criterion measure in predictive validation studies of hearing aid selection procedures.

Acoustic-reflex activity and behavioral thresholds following exposure to noise.

The relationships between properties of the acoustic reflex and temporary threshold shift (TTS) were examined in eight subjects exposed to a 95 dB SPL, 1.0-kHz octave-band noise for 4 h. The specific pattern of TTS obtained from this exposure was consistent with the expected sensitivity changes along the cochlear partition. Maximum decrease in behavioral thresholds was noted at 1.4 kHz with significant TTS also occurring at 2.0 and 4.0 kHz. Behavioral threshold at 0.5 kHz, one octave below the center frequency of exposure, was not affected. Significant reflex threshold shift (RTS) occurred at 1.4 and 2.0 kHz. In addition, RTS was noted at 0.5 kHz in the absence of any change in behavioral sensitivity at that frequency. Magnitude of the acoustic reflex was examined from threshold to 10-dB sensation level. A systematic reduction in magnitude was noted during the noise exposure for 1.4 and 2.0 kHz. The same pattern did not emerge for 0.5 kHz. Magnitude of the acoustic reflex pre-exposure was significantly correlated to TTS at 1.4 kHz. Changes in acoustic reflex thresholds and magnitudes followed the same time course as changes in behavioral thresholds during the growth and recovery periods.