Kubovy Perception Lab
UVA Lab


Jerk, Acceleration, and Velocity

From the previous experiment it appeared that time was the key factor in determining the strike's impact on perceived note duration. You will recall, however, that the previous experiment ignored acceleration and its derivative, "jerk."

In this experiment three conditions were created. In the first the dot rebounded, just as in the previous experiment, with a constant velocity. In this condition, acceleration and jerk were not present. In the second condition the dot rebounds and then constantly decelerates to a stop. Since the deceleration is constant there is no jerk in this movement. In the third condition the original videos were used so that acceleration and jerk were both present. All three conditions were matched for time and distance travelled, such that the long videos matched across each condition and the short videos matched across each condition.

You might be wondering why we evaluated jerk, which is the change in acceleration over time. We considered it because jerk indicates that there is a living source that is powering the movement, or an external force that is altering the movement path. Gravity regularly accelerates objects at a constant acceleration, but if something speeds up and slows down and varies its acceleration this implies that something more than the force of gravity is at work. This might reasonably cause participants to process motion with jerk included as lifelike, and motion without jerk as derived from an inanimate object.

We hypothesized that acceleration and jerk would not impact the behavior of the videos. The results confirmed our hypothesis, leaving us to conclude that time of travel after rebound is in fact the key factor in determining how a strike will alter perception of an associated note.

 

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