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. 2001 Feb 13;98(5):2826–2831. doi: 10.1073/pnas.041604998

Figure 2.

Figure 2

A model for predicting EEOAE output under acoustical modulation. (a and b) Schematic basal cross-sections through the high-frequency area of the auditory papilla of Tiliqua rugosa to illustrate the influence of hair-cell orientation on EEOAE output for two possible locations for the motor driving the cochlear amplifier. The tallest stereovilli of the hair-cell groups on either side face the middle of the papilla. A hair-cell lateral membrane motor would drive all cells to elongate and shorten in phase (a, arrows) and EEOAE from different populations would add constructively. For a bundle-based motor, however, oppositely oriented bundles would move 180° out-of-phase (b, arrows) and EEOAE add destructively. tm, tectorial membrane; sc, supporting cells; hc, hair cell, hcb, hair-cell stereovillar bundle. When low-frequency sound is applied, the output from hair cells of one orientation decreases, whereas that of the other increases, the force from each type being of the same phase in the case shown in a and c--e and of opposite phase in the case b and f--h. A 5% excess of cells of one polarity is assumed, allowing a small EEOAE response at the resting point in f–h. The model uses the same frequency ratio between electrical and acoustical stimuli as in a–c in Fig. 4 (9.25:1). The time axes cover just over 1.5 cycles of the modulator. (c—e) EEOAE output (thin lines) of a model simulating lateral membrane motors stimulated by ac current and modulated by a low-frequency sound (thick line, placed on arbitrary axes relative to the EEOAE). Compared with c, the relative sound pressure of the modulator is increased by 10 and 20 dB in d and e, respectively. (f—h) As in c and d, but for motors in the hair cell bundle. Modulation increases EEOAE from one set of cells and reduces it from the other, depending on the phase of the modulating sound. Compared with f, the sound pressure of the modulator is increased by 10 and 20 dB in g and h, respectively. In e and h, the vertical lines emphasize the roughly 180° phase shift in the EEOAE in h at each half cycle of the modulator.