Abstract
Purpose: Past research has shown that compared to non-biological motion, biological motion is different because it (a) has longer temporal summation periods and (b) temporal summation depends upon the cycles presented. We sought to determine whether the inclusion of form or more complex types of non-biological motion eliminated these temporal summation differences. Method: Four point-light target motions were used: rotation of randomly placed dots (simple motion), a rotating square (simple motion with form), a front-end loader (complex non-biological motion with form), and a human walker (complex biological motion with form). A staircase procedure was used to determine the number of mask dots necessary to reach threshold in a left/right facing task or clockwise/anti-clockwise rotation task. Masks were created from scrambled versions of both facings or both rotation directions of the target motions. The targets were presented for one of seven durations from 165 to 2824 msec. Results: The motion of the front-end loader and the human walker had similar temporal summation curves and these temporal summation curves were distinctly different than the temporal summation curves associated with rotating dots or a rotating square. Conclusions: The complexity of the motion involved in the display, regardless of whether the motions are biological or non-biological, may determine temporal summation functions. Temporal summation differences between biological and non-biological motion described in past research may have resulted from the simplicity of the non-biological motion used in those studies.