Time, observation, movement

Traditionally, a sharp distinction was made between conscious perception of elapsed time, considered a key attribute of cognition, and automatic time processes involving basic sensory and motor functions. Recently, however, this dichotomous view has been challenged on the ground that time perception and timed actions share very similar features, at least for events lasting less than a second. For both perception and action, time estimates require internally generated and/or externally triggered signals, because there is no specific sensory receptor for time in the nervous system. We argue that time can be estimated by synchronizing a neural time base either to sensory stimuli reflecting external events or to an internal simulation of the corresponding events. We review evidence in favor of the existence of distributed, specialized mechanisms, possibly related to brain mechanisms which simulate the behavior of different categories of objects by means of distinct internal models. A critical specialization is related to the animate-inanimate distinction which hinges on different kinematic and kinetic properties of these two different categories. Thus, the time base used by the brain to process visual motion can be calibrated against the specific predictions regarding the motion of biological characters in the case of animate motion, whereas it can be calibrated against the predictions of motion of passive objects in the case of inanimate motion.