The above operations deal with time-varying but spatially fixed patterns of excitation on receptors. Another important input modality is the motion of a fixed pattern shape of contrasting (0.1) excitation in a specified direction at unit velocity, u. (|u| = 8/T.)

9. The direction of movement, y, of an object may be sensed by an application of the T1(a, b) and T2(a, b) operators, and a sensitivity to increased or decreased excitation at a point passed by the moving edge (contrast boundary) by using the T1(a) and T2(a) operators. Thus,

@ t = nT IFF the excitation at a goes 0 ^ 1 @ nT AND this event is NOT preceded at t = (n - 1)T by brightening (0 ^ 1) at b. [Note: The M1 = 1 primary requirement is brightening at a at t = nT; any time course and change of illumination at b is permissible to get output except brightening at t = (n - 1)T.]

For motion causing a decrease in excitation going from a to b,

Note that both M1 and M2 operators are dyadic and one dimensional; they both require unit velocities, u, to work. M1 and M2 operators respond ambiguously to ON (M1 = 1) and OFF (M2 = 1) over a and b together.

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