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In animals, the MOCR has also been shown to be active dur-
8
ing a visual attention task. This suggests another role, turning
down input from one sense when paying attention to another. This suggests that the MOCR is active in auditory attention, in addition to the reflexive response to sound discussed above.
Why would it be beneficial for the auditory system to decrease gain in response to sound? The basic temporal effect is the ability to detect a signal at a lower signal-to-noise ratio (SNR) after a precursor. In certain conditions, decreasing gain may improve the SNR at the output of the cochlea because cochlear amplification decreases with sound level. For example, if the noise output is lower than the signal out- put, a decrease in gain will turn down the noise more than the signal, thus increasing the SNR. The MOCR may adjust the auditory system to maximize the SNR in varying levels of background noise. Thus our person with the cat-like reflexes may be a star athlete not only because of muscle feedback, but also because auditory feedback allows communication in background sound levels ranging from the quiet of practice to the roar of a game.AT
References for further reading
1 J. J. Guinan, Jr., “Olivocochlear efferents: Anatomy, physiology, function, and the measurement of efferent effects in humans,” Ear and Hearing 27, 589-607 (2006).
2 S. F. Maison and M. C. Liberman, “Predicting vulnerability to acoustic injury with a noninvasive assay of olivocochlear efferent strength,” J. Neuroscience 20, 4701–4707 (2000).
3 E. Zwicker, “Temporal effects in simultaneous masking by white-noise bursts,” J. Acoust. Soc. Am. 37, 653–663 (1965).
4 D. McFadden and C. A. Champlin, “Reductions in overshoot dur-
ing aspirin use,” J. Acoust. Soc. Am. 87, 2634–2642 (1990).
5 C. A. Champlin and D. McFadden, “Reductions in overshoot following intense sound exposures,” J. Acoust. Soc. Am. 85,
2005–2011 (1989).
6 E. A. Strickland, “The relationship between frequency selectivi-
ty overshoot,” J. Acoust. Soc. Am. 109, 2063–2073 (2001).
7 E. A. Strickland, “The temporal effect with notched-noise maskers: Analysis in terms of input-output functions,” J. Acoust.
Soc. Am. 115, 2234–2245 (2004).
8 P. H. Delano, D. Elgueda, C. M. Hamame, and L. Robles,
“Selective attention to visual stimuli reduces cochlear sensitivity in chinchillas,” J. Neuroscience 27, 4146–4153.
Elizabeth A. Strickland received her PhD in experimental psychology from the University of Minnesota in 1994. Following a year of postdoctoral work at the University of Florida, she joined the faculty of Purdue University. She is cur- rently an associate professor in the Department of Speech, Language, and Hearing Sciences, as well as the Chair of the Technical Committee on Psychological and Physiological Acoustics of the Acoustical Society of America. Her
research focuses on temporal processes in normal and impaired hearing.
Skyler G. Jennings is an Au.D./Ph.D. student at Purdue University and a Doctor of Audiology extern at the Indiana University Medical Center. In addition to his clinical responsibilities, he holds a half-time National Institutes of Health pre-doc- toral research fellowship and is a resi- dent assistant in the University’s resi- dence halls.
28 Acoustics Today, October 2007