Chinchilla middle ear transmission matrix model and middle-ear flexibility.

The function of the middle ear (ME) in transforming ME acoustic inputs and outputs (sound pressures and volume velocities) can be described with an acoustic two-port transmission matrix. This description is independent of the load on the ME (cochlea or ear canal) and holds in either direction: forward (from ear canal to cochlea) or reverse (from cochlea to ear canal). A transmission matrix describing ME function in chinchilla, an animal commonly used in auditory research, is presented, computed from measurements of forward ME function: input admittance YTM, ME pressure gain GMEP, ME velocity transfer function HV, and cochlear input admittance YC, in the same set of ears [Ravicz and Rosowski (2012b). J. Acoust. Soc. Am. 132, 2437-2454; (2013a). J. Acoust. Soc. Am. 133, 2208-2223; (2013b). J. Acoust. Soc. Am. 134, 2852-2865]. Unlike previous estimates, these computations require no assumptions about the state of the inner ear, effectiveness of ME manipulations, or measurements of sound transmission in the reverse direction. These element values are generally consistent with physical constraints and the anatomical ME "transformer ratio." Differences from a previous estimate in chinchilla [Songer and Rosowski (2007). J. Acoust. Soc. Am. 122, 932-942] may be due to a difference in ME flexibility between the two subject groups.