The difference between the perception of absolute and relative motion: a reaction time study.

We used a reaction-time paradigm to examine the extent to which motion detection depends on relative motion. In the absence of relative motion, the responses could be described by a simple model based on the detection of a fixed change in position. If relative motion was present, the responses could be modelled using characteristics of motion detectors. Comparing reaction times when relative and absolute velocity are equal with ones when relative velocity is twice the absolute velocity reveals that these detectors measure relative motion.