Fig. 1.

The time course and sign of contra-noise effects are variable. Contra-noise effects were measured 244 times in 52 mice, with ipsilateral f₂ at 16 kHz and primary levels set to produce a distortion product otoacoustic emissions (DPOAE) of 0 dB SPL. A: each of the 244 runs was assessed by one-way ANOVA: in 115 cases (black Xs), responses during the contra noise were statistically indistinguishable from those before noise onset (P > 0.01). Runs with statistically significant effects were classified into 1 of 4 response types, and mean (±SE) ΔDPOAE is plotted for each: 1) enhancement (purple triangles), 2) rapid-onset suppression with slow adaptation (black circles), 3) slow-onset, buildup suppression (yellow circles), or 4) nonadapting suppression (red triangles). Time resolution is ∼4.5 s/point. ΔDPOAE is normalized re the mean prenoise DPOAE amplitude. B: mean ΔDPOAE (averaged over the contra-noise epoch) for each of the 244 runs is plotted as a function of contra-noise level, color-coded according to response “type” shown in A. Inset: relative frequency of occurrence of each response type for each anesthesia regimen. U/X, urethane-xylazine; K/X, ketamine-xylazine. C: same data as in B, but coded according to anesthetic regimen.