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The Half-Octave Shift Revisited: Evidence from Middle-Ear Power Transmittance and Stimulus Frequency Otoacoustic Emissions in Humans
Abstracts of the Annual MidWinter Research Meeting of the Association for Research in Otolaryngology (2013)
  • Shaum P. Bhagat, University of Memphis
  • Chelsea Kilgore, University of Memphis
Abstract
Background
Following exposure to an intense tone, the largest temporary otoacoustic emission level shift (TES) occurs approximately one-half octave above the exposure frequency. Variation in TES between individuals may be partially explained by individual differences in middle-ear sound transmission. The aim of this study was to examine the contribution of middleear sound transmission to measured amounts of TES.

Methods
Pre-exposure measurements of middle-ear power transmittance (MEPT) and stimulus frequency otoacoustic emissions (SFOAE) at 1.4 and 2.0 kHz were obtained from normal-hearing adults. SFOAE levels were derived from probe alone and probe plus suppressor conditions. SFOAE measurements were repeated as a check of test/retest reliability. Following a 1- minute exposure to a 105 dB SPL tone at 1.4 kHz, SFOAE measurements at 1.4 and 2.0 kHz were completed at 2 and 4 minutes after the exposure. Shifts in SFOAE levels at 2 minutes (TES2) and 4 minutes (TES4) were calculated.

Results
The mean SFOAE test/retest reliability was within 1 dB at both 1.4 and 2.0 kHz. The mean amount of TES was greater than one standard deviation above the mean value of test-retest reliability only at 2.0 kHz. The amount of TES2 and TES4 was similar at both test frequencies. Trends in the data indicated that MEPT was related to the amount of TES. Individuals with higher MEPT values at 1.4 and 2.0 kHz tended to have larger TES4 at 2.0 kHz, while individuals with lower MEPT values tended to have smaller TES4 at 2.0 kHz.

Conclusion
The results of this study are consistent with previous research indicating the maximum effect of tonal overexposure occurs one-half octave above the exposure frequency. For SFOAEs, the amount of TES4 appears to be related to a) MEPT at the exposure frequency and b) MEPT at one-half octave above the exposure frequency. These findings suggest that MEPT of intense sound may play a role in explaining some of the variability seen in the amount of TES across individuals. Exploration of the role of MEPT in temporary threshold shift is warranted. 
Publication Date
2013
Citation Information
Shaum P. Bhagat and Chelsea Kilgore. "The Half-Octave Shift Revisited: Evidence from Middle-Ear Power Transmittance and Stimulus Frequency Otoacoustic Emissions in Humans" Abstracts of the Annual MidWinter Research Meeting of the Association for Research in Otolaryngology Vol. 36 (2013) p. 820 - 821
Available at: http://works.bepress.com/shaum-bhagat/83/