Basilar membrane responses to broadband stimuli

Basilar membrane (BM) responses to two types of broadband stimuli-clicks and Schroeder-phase complexes--were recorded at several sites at the base of the chinchilla cochlea. Recording sites (characteristic frequency, CF, in the range of 5.5-18 kHz) span the 1-4-mm basal region of the basilar membrane. BM responses to clicks consisted of undamped oscillations with instantaneous frequency that increased over time until it reached a value around CF. The time constant of this glide is CF dependent. Throughout the entire region under study, BM vibration exceeded umbo motion by up to 60 dB. Nonlinear properties of BM responses to clicks resemble those found in the more studied 8-10-kHz region. Amplitude spectra of Schroeder-phase complex stimuli, which consist of a series of sinusoidal components summed in negative (-SCHR) and positive Schroeder phase (+SCHR), are flat. The envelope of BM responses to +SCHR stimuli contains valleys, or dips, that are wider than those found in responses to the -SCHR stimuli. Hence, BM responses to the former stimuli are "peakier" than responses to the latter. Differences in response waveforms are less obvious in linear cochleae. Suppression of a near-CF tone by -SCHR stimuli was larger than that evoked by +SCHR stimuli.