The experiments investigated how two adult captive chimpanzees learned to navigate in an automated interception task. They
had to capture a visual target that moved predictably on a touch monitor. The aim of the study was to determine the learning
stages that led to an efficient strategy of intercepting the target. The chimpanzees had prior training in moving a finger
on a touch monitor and were exposed to the interception task without any explicit training. With a finger the subject could
move a small "ball" at any speed on the screen toward a visual target that moved at a fixed speed either back and forth in
a linear path or around the edge of the screen in a rectangular pattern. Initial ball and target locations varied from trial
to trial. The subjects received a small fruit reinforcement when they hit the target with the ball. The speed of target movement
was increased across training stages up to 38 cm/s. Learning progressed from merely chasing the target to intercepting the
target by moving the ball to a point on the screen that coincided with arrival of the target at that point. Performance improvement
consisted of reduction in redundancy of the movement path and reduction in the time to target interception. Analysis of the
finger's movement path showed that the subjects anticipated the target's movement even before it began to move. Thus, the
subjects learned to use the target's initial resting location at trial onset as a predictive signal for where the target would
later be when it began moving. During probe trials, where the target unpredictably remained stationary throughout the trial,
the subjects first moved the ball in anticipation of expected target movement and then corrected the movement to steer the
ball to the resting target. Anticipatory ball movement in probe trials with novel ball and target locations (tested for one
subject) showed generalized interception beyond the trained ball and target locations. The experiments illustrate in a laboratory
setting the development of a highly complex and adaptive motor performance that resembles navigational skills seen in natural
settings where predators intercept the path of moving prey.
Keywords Interception - Anticipatory control - Hunting - Navigation -
Pan troglodytes