Fig. 8.
Temporal and spatial limits of apparent motion for the initiation of normal pursuit. Each graph contains one symbol for each combination of temporal separation (Δ*t*) and spatial separation (Δ*x*). The symbol type expresses mean eye velocity as a percentage of that evoked by targets of the same apparent velocity but with a Δ*t* of 4 ms: large solid circles, eye velocity within 90% of normal; large open circles, eye velocity within 80–90% of normal; progressively smaller circles indicate progressively slower eye velocities as defined by the key in *B*. The diagonal lines correspond to fixed values of apparent target velocity, indicated by the numbers along the top and right edges of each panel.*A* and *B*: experiments designed to tile a large range of possible values of Δ*t* and Δ*x* (*monkeys Da* and *Fi*).*C–F*: experiments using a closer spacing of values of Δ*t* and Δ*x* over a more limited range, to allow a more complete sampling of the range where pursuit initiation becomes impaired (*monkeys El, Mo, Na,* and*Ka*). Each point is based on the mean eye velocity in a 20-ms interval centered 70 ms after the initiation of normal pursuit for *monkeys Da, Fi,* and *El,* and centered 50 ms after the initiation of pursuit for *monkeys Mo, Na,* and *Ka*.