ABSTRACT
One of the more baffling aspects of the organization of behavior is that an action that we regard as unitary at one level of analysis dissolves into a bewildering variety of diverse descriptions when we shift to a lower level of analysis and description. When analyzed at the level of leg movements, “moving forward” is not a unitary phenomenon. The action of moving forward can refer to quite different sequences of leg movements. Take for example the sequence the cockroach uses when moving very slowly forward. First it lifts its rear leg (R3) and advances it forward. Having planted the right rear leg, it lifts and advances the right middle leg (R2) then the right front leg (R1). The sequence of leg movements progresses along the body in the direction the body is moving, in this case the forward direction. Such sequences are termed metachronal. Having moved all three legs on its right side in this metachronal sequence, the roach now lifts and advances the left rear leg (L3), then the left middle leg (L2), and finally the left front leg(L1). The description of this behavior when analyzed in terms of the sequence of leg movements is R3, R2, R1, L3, L2, L1, R3, etc. On the other hand, we know from Chapter 1 that when the roach moves forward with maximum rapidity the sequence of leg movements is (R3L2R1), (L3R2L1), (R3L2R1), etc., where the legs enclosed by parentheses are moved simultaneously.
