Perception & Psychophysics

, Volume 64, Issue 1, pp 15-31

First online:

Trajectory forms as a source of information about events

  • Michael M. MuchiskyAffiliated withDepartment of Psychology, Indiana University
  • , Geoffrey P. BinghamAffiliated withDepartment of Psychology, Indiana University Email author 


The ability to use trajectory forms as visual information about events was tested. A trajectory form is defined as the variation in velocity along a path of motion. In Experiment 1, we tested the ability to detect trajectory form differences between simulations of a freely swinging pendulum and a handmoved pendulum. The trajectoryform of the freely swinging pendulum was symmetric around the midpoint, whereas the hand moved was not. In Experiment 2, we isolated trajectory form information by varying the amplitudes of events while holding their periods constant. Straight path versions of the harmonic events from Experiment 1 were tested. In Experiment 3, we tested sensitivity to symmetrical peakening or flattening of trajectory forms. Participants detected small differences in all three experiments. In Experiment 4, we tested the ability to identify specific events based only on differences in trajectory forms. Participantswere able to identify four different events. We investigated properties of trajectory forms that might potentially be detected and used as information, and we found that the curvature yielded good results.