Tuning properties of turtle auditory nerve fibers: evidence for suppression and adaptation.

Second-order reverse correlation (second-order Wiener-kernel analysis) was carried out between spike responses in single afferent units from the basilar papilla of the red-eared turtle and band limited white noise auditory stimuli. For units with best excitatory frequencies (BEFs) below approximately 500 Hz, the analysis revealed suppression similar to that observed previously in anuran amphibians. For units with higher BEFs, the analysis revealed dc response with narrow-band tuning centered about the BEF, combined with broad-band ac response at lower frequencies. For all units, the analysis revealed the relative timing and tuning of excitation and various forms of inhibitory or suppressive effects.