The phase response of primary auditory afferents in a songbird (Sturnus vulgaris L.).

The effects of stimulus frequency and intensity on phase-locking characteristics of cochlear ganglion cells were studied in the starling. All cells showed phase-locking to tone stimuli within their response area. Phase-locking at CF is found on average 9 dB below discharge rate threshold. Phase-locking is best at 0.4 kHz and deteriorates with increasing frequency almost independently of CF. No phase-locking was evident for test frequencies above 3-4 kHz. Phase-locking in cells with CFs above 1.0 kHz is better below CF than at CF. For constant sound pressure, an increase in stimulus frequency always produced an increase in phase lag of the neural response. The phase vs. frequency data obtained at constant sound pressure can be reasonably approximated by straight line functions. The slopes of these functions indicate the latency of the neural response, and are correlated with the CFs of the respective cells; the latency tends to be longer in low-CF cells and shorter in high-CF cells. The latency decreases by 0.04 ms per 1 dB sound pressure increase. The response phase at CF is nearly stimulus level-independent. Increasing stimulus intensity causes increasing phase lag below CF and decreasing phase lag above CF. These results are compared to findings in other vertebrates and demonstrate the similarities of phase-locking characteristics despite the substantial anatomical differences among the vertebrate groups.