Time perception during apparent biological motion reflects subjective speed of movement, not objective rate of visual stimulation

We have investigated links between biological motion perception and time perception. Participants compared the durations of two paired visual frames, inside which task-irrelevant sequences of static body postures were presented. The sequences produced apparent movements of shorter and longer path lengths, depending on the sequential order of body postures (ABC or ACB). Shorter and longer path lengths were paired with shorter and longer interstimulus intervals (ISIs) to produce path/ISI congruent sequences with intermediate subjective speeds and path/ISI incongruent sequences with slowest and fastest subjective speeds. Participants compared the duration of the visual frames surrounding these sequences; body postures and biological motion were irrelevant. The ability to discriminate the duration of the frames (as measured by the just noticeable difference, JND) was reduced for pairs of path/ISI congruent sequences as compared to pairs of path/ISI incongruent sequences. That is, duration discrimination improved when implied speed differed between the two sequences of a pair compared to when the implied speed was the same. Since stimuli showed no actual movement and were fully matched for lower-level visual input and objective stimulus durations, our findings suggest an involvement of higher-order visual or even motor areas in temporal biases during apparent biological motion perception. We show that apparent speed is the primary dimension of such percepts consistent with a dominant role of movement dynamics in the perception of other people's actions. Our results also confirm an intimate relation between time perception and processing of human movement