Figure 2.

Response of the model BM during sound stimulation to the stapes (30 kHz), for three values of OHC motility. All panels show BM motion vs. stapes motion, on a linear scale. (a) Magnitude, no OHC motility. Motion peak occurs 2.5 mm from the base of the cochlea; there is also a smaller, secondary peak 3.9 mm from the base. The rotation of the pillar cells as a single unit about the spiral lamina is indicated by the linear increase in motion to the edge of the outer pillar cells (40 μm from spiral lamina). (b) Magnitude, normal OHC motility (330 pN/nm). Motion peak occurs 3.0 mm from the base, and the secondary peak is no longer present. Motion at the center of the membrane at the peak is ≈30 dB greater than that with no OHC motility. Motion near the base is unchanged. At each position from the base, motion across the BM width is now asymmetric. (c) Magnitude, enhanced OHC motility (560 pN/nm). Motion peak occurs 2.6 mm from the base. BM motion is less than that observed with normal OHC motility. The largest change occurs beneath the pillar cells, producing an exaggerated inflexion point at the edge of the outer pillar cells. (d) Phase, no OHC motility. Monotonic accumulation of phase with distance from the base exceeds 360°, which indicates the presence of a travelling wave. (e) Phase, normal OHC motility. There is now a difference in BM phase across its width. (f) Phase, enhanced OHC motility. There is a slightly enhanced phase variation across the width of the BM.