Time perception of action photographs is more precise than that of still photographs

A photograph of an action contains implicit information about the depicted motion. Previous studies using either psychophysics or neuroimaging suggested that the neural processing of implied-motion images shares some features of real-motion processing. According to the hypothesis that the target depicted in photographs with implied motion is mentally represented as continuing in motion, such kind of photographs should be processed by the brain similarly to the individual frames of a running movie. In order to decode the functional significance of a movie, we must be able to estimate the duration of each frame and the time interval between successive frames as precisely as possible. Therefore, under naturalistic conditions, one would expect that the precision of time duration estimates is higher for action pictures than for still pictures. To test this prediction, we asked human observers to compare the variable duration of test photographs with the reference duration of their scrambled version. We found that, as expected, the duration of photographs with implied motion was discriminated better than the duration of photographs without implied motion. We also found that the average reaction time for the discrimination of photographs with implied motion was longer than that for photographs without implied motion, suggesting that the processing of implied motion involves longer and/or slower neural routes to compute time duration. This longer processing may depend on the engagement of two visual systems in parallel, one for processing form and the other one for processing implied motion. The perceptual decision about time duration would occur after the convergence of signals from these two pathways.