FIG. 7.

Hearing threshold data from C. perspicillata. Behavioural threshold (Koay et al. 2002) and auditory cortex neurophysiological threshold (Esser and Eiermann 1999) were both obtained under free field conditions. DPOAE threshold (green lines: 2f1–f2 (solid), f2-f1 (dashed)) were measured with the in-ear acoustic coupler which prevented modification of threshold sensitivity by the outer ear. The free field curves are characterised by an insensitivity between 40 and 55 kHz which is absent in the DPOAE data.