What Newton did not know about Newton’s cradle: Separating visual routines for cause and effect

In Newton’s cradle a moving object collides with a line of touching stationary objects, causing the object at the very end of the line to move. This demonstration of Newton’s first law of motion is fascinating to watch because the cause and effect of the motion are spatially separated. Here, in a modified version of Newton’s cradle, we exploit this separation in a visual adaptation paradigm to show that there are separate visual routines for detecting cause and effect in a causal interaction. We presented launching events in which a moving disc stopped next to another disc with varying degrees of overlap, and asked observers to indicate whether the first disc caused the second disc to move, or whether the first disc simply passed a stationary one. We fitted psychometric functions to each observer’s reports as a function of disc overlap and determined how these functions were affected by the prolonged presentation of a modified version of Newton’s cradle (i.e., the adaptor). Critically, we obtained psychometric functions for the perceived causality at the cause location and at the effect location in Newton’s cradle and we observed significant negative aftereffects at both the cause and at the effect location (Experiment 1 and 2). Observers reported fewer launches at these locations only when the motion direction of the test event was the same as the adaptor’s motion direction (Experiment 1). Critically, the adaptation was spatially specific: Perception of launches at the location in-between the cause and the effect locations was not affected by adaptation (Experiment 2). These results provide compelling evidence that the perception of causality integrates information from both the cause and the effect location. This integration allows the detection of causal interaction even when the cause and effect are spatially separated in the visual environment.