Fig. 4.

Schematic diagram illustrating the generation of CM components. The diagram shows phase lags relative to the stimulus at the stapes (lag increasing downward) of traveling waves (solid) and electrical signals (dotted). The electrical signals spread instantaneously throughout the cochlea (i.e., no additional phase lags) but decay exponentially with distance from the source. As in the classical model, the early-latency component arises in the tail region of the stimulus-evoked forward traveling wave, where BM phase varies slowly with location and currents from the hair cells sum constructively (black dotted box). The resulting CM component reaches the round window with essentially no delay (black dotted arrow). Although local CM currents are large near the peak of the forward traveling wave, the classical model predicts that rapid BM phase variations cause near total cancelation of the CM from this region. However, the introduction of cochlear electrical irregularities allows a region of coherent summation of CM sources to emerge (red dashed box). As a result, CM components with delays close to the forward travel BM time to the CF place (middle latency) reach the round window. Near the CF place, through a process of coherent reflection (R) from micromechanical irregularities, a reverse traveling wave arises (solid red) that is partially transmitted to the middle ear (OAEs) and partially reflected toward the cochlea (R_s), giving rise to a secondary forward traveling wave (solid blue). The late-latency components (dotted blue) represent the sum of currents produced by the cells located in the overlapping tail regions of the reverse and the secondary forward traveling waves (dotted blue box)