Fig. 1.

Diagram of experiments and temporal characteristics of the stimulus. A, The right eye (see drawing of half locust head on right) was stimulated from the side by presenting squares of half-size l approaching at a constant velocity v toward the center of the eye at 90° relative to the animal’s body axis. Because the stimulus is monocular, the variable of importance is the time course of the angular size of the object subtended at the retina, θ(t). B, Time course of θ(t) and of the angular velocity ψ(t) as a function of time before collision for a slow velocity of approach (or a large object). Both functions are nonlinear in time; see Equations 2 and 3. Final angular size at collision: 180°; i.e., the object covers the entire visual field.