Figure 4.

Principal components of directional cells and inputs to two motion models, with various rotations (0°–180°, every 30°, left to right). (A, Upper) Example of a directional cell for which there was one particular rotation angle (circled) at which one of the components was totally monophasic (biphasic index <0.1). This result was seen in 12/17 cells. (Lower) Example of a directional cell for which at one rotation angle (circled) one component was minimally biphasic (index <0.4) but not totally monophasic. This result was seen for the remaining five cells. (B) Linear combinations of two components used in models of directional cells. (Upper) The pair of temporal profiles used in the Adelson–Bergen (2) model. (Lower) The pair of temporal profiles of a model that produces directional cells by combining two biphasic cells with identical temporal impulse response shapes (average waveform of the strongly biphasic cells in our sample) but different latencies. Note that for neither of these models is there a rotation angle at which the least biphasic component has a biphasic index of less than 0.45. Neither thus can account for any of our directional cells.