A reconsideration of sound calibration in the mouse.

Although it is traditional to perform sound calibrations in anesthetized animals by placing a probe-tube microphone near the tympanic membrane, these measurements are inaccurate at high stimulus frequencies where hearing must be quantified in the mouse. Hence, our motivation to develop another approach using the mouse ear canal as a coupler. Results of real-ear-canal calibrations indicate that an average calibration can be used to estimate sound pressure levels in the three mouse strains tested. Similar estimates were also obtained using a tubing coupler, whose volume was comparable to that of the ear canal, thereby offering a simpler alternative. In addition, real-head calibrations were also performed to provide a procedure that can be used in situations where the ear is not dissected, as in measurements of the auditory brainstem response. Calibrations for open, rather than closed, sound-delivery systems were also evaluated using a modified method of substitution.