Figure 4: Group delay demonstrates the propagation of travelling waves.

(a) Representative group delay calculated from the phase curves from a cohort of eight chickens. The group delay was larger for more apical locations and for higher-frequency stimuli. Error bars show the s.e.m. (b) Vibration measurements for eight different locations along the length of the basilar papilla in another representative chicken. A 300 Hz stimulus was presented and the time differences were determined between the first vibratory peak at each location (blue line) referenced to the basal-most recording site (red line). All magnitudes were scaled to be identical to make it easier to assess for time delays, so the y axis is unlabelled. It took longer for more apical sites to begin vibrating, thus demonstrating delays associated with travelling wave propagation. The distance from the basal-most recording location, the percent distance from the base, and the time delay are provided for each measurement.