(after Baker and Rosen, 2006)
This figure illustrates auditory filter shapes derived by Baker and Rosen (2006) using simultaneous notched-noise masking. In that study filter shapes were measured over a range of frequencies and levels and parameters for a fitted shape that was made up of a ROEX(p,w,t) model on the low frequency side and a ROEX(p) model on the high-frequency side. For the low-frequency side the 'w' parameter varied with tone level, and equations were derived to explain how the different parameters varied across frequency. The analyses of Baker and Rosen also assumed that the filter gain was zero (and linear) at a point in the low-frequency tail - in this figure this is assumed to be the case at a frequency equal to 0.4 x filter centre frequency. This figure is designed as a 'teaching tool' rather than an accurate illustration of cochlear gain or function, but illustrates changes in filter shape across frequency and level. Other evidence suggests that the change in gain with signal level shown here is an underestimate of the nonlinear changes observed using other techniques.
Richard J. Baker, Stuart Rosen; Auditory filter nonlinearity across frequency using simultaneous notched-noise masking. J. Acoust. Soc. Am. 1 January 2006; 119 (1): 454–462. https://doi.org/10.1121/1.2139100