SUMMARY1. Intracellular potentials were recorded with micropipettes from hair cells with free-standing stereocilia in the cochleae of anaesthetized alligator lizards.2. Wave forms of intracellular responses to click stimuli were classified into three types: hair cells, supporting cells, and untuned cells. We studied primarily the responses of hair cells to tonal stimuli.3. For most frequencies, f, and levels, P, of tone-burst stimuli, the response envelope of the receptor potential increases monotonically at the tone-burst onset, and decreases monotonically at tone-burst offset. Overshoot in the envelope of the response at the onset and offset of tone bursts is observed only for tone bursts of low f, high P, and short ( and V' components was measured by means of iso-voltage (iso-V0 and iso-V,)contours. Iso-V0 and iso-V' contours are V-shaped: the maximum sensitivity occurs at a characteristic frequency (c.f. ). The shapes of these contours near the c.f. depend on the values of V0 and V1 at which the contours were measured and are sharper for lower values of V1 and V1. The mean slopes of the low-and high-frequency sides of these contours are: -45-0 and + 85-1 dB/decade for iso-V0 contours (n = 26), and -33'6 and + 103'8 dB/decade for iso-V1 contours (n = 28).6. The receptor potential has non-linear properties. The magnitudes and phase angles of V0, 'l, V2, and V3 receptor-potential components were measured as a function of P for different f. The slopes of level functions (the dependence of log V0 and log V1I on log P) were measured at low levels for different f.
T. HOLTON AND T. F. WEISSdiffering from c.f. by more than a half-octave, the slope for VT is between 1 and 2 with a mean of 1P3; the slope for V1 is about 1, i.e. V11 increases approximately linearly with P. For frequencies near c.f., the slopes for V0 and V1 are approximately 0-8 and 0 5, respectively, indicating the presence of a compressive non-linearity. An effect of this frequency-dependent non-linearity is to sharpen the frequency selectivity at lower response magnitudes for f near c.f.7. The receptor potential shows low-pass filtering. Whereas the maximum response magnitude of V0 (i.e. the saturation value measured at high P) does not depend on f, the maximum Vj decreases by approximately 20 dB/decade with increasing f. Values of IIJ1I measured at a constant value of V0 also decline by approximately 20 dB/decade.8. Many of the results are consistent with the predictions of a three-stage model of the generation of the receptor potential. The first stage, which represents the mechanical properties ofthe middle and inner ear, is a linear, time-invariant, band-pass filter; the second stage, which represents mechanoelectric transduction in hair cells, is a zero-memory non-linearity; the third stage, which represents the electrical properties of hair cells, is a linear, time-invariant, low-pass filter. However, the results differ from the model predictions for low-level acoustic stimuli near c.f., and indicate the presence of a frequency-dependent compr...