Mental extrapolation of target position is strongest with weak motion signals and motor responses

Some accounts hold that the position of moving objects is extrapolated either in visual perception or visual short-term memory ("representational momentum"). However, some studies did not find forward displacement of the final position when smooth motion was used, whereas reliable displacement was observed with implied motion. To resolve this conflict, the frequency of position changes was varied to sample motion types between the extreme cases of implied and smooth motion. A continuous function relating frequency of target change and displacement was found: Displacement increased when the frequency of position changes was reduced. Further, the response mode was varied. Probe judgments produced less forward displacement than motor judgments such as mouse or natural pointing movements. Also, localization judgments were susceptible to motion context, but not to variations of probe shape or expectancy about trajectory length. It is suggested that forward displacement results from the extrapolation of the next step in the observed motion sequence.