Abstract
Accurate timing over the sub-second scale is essential for a range of human perceptual and motor activities, but the mechanisms for encoding this time scale remain poorly understood. A series of experiments from our laboratory indicates that perception of time is tightly linked to perception of external position. Firstly, adaptation to fast drifting gratings cause temporal distortions that are spatially specific in external spatial coordinates, implicating craniotopic receptive fields (Burr et al., Nature Neuroscience, 2007). Compression of perceived duration (interval separation between distinct events) occurs for stimuli presented peri­saccadicaly, at the time when craniotopic receptive fields are being updated (Morrone et al., Nature Neuroscience 2005). To understand better these phenomena, we measured perceived time of stimuli during saccades, with a cross-modal temporal-order-judgment and a bisection technique to study time perception: subjects reported whether a flashed bar appeared earlier or later than a single beep, or the midpoint of two beeps (200 ms separation). Time perception was considerably distorted during saccades: flashed bars were perceived either earlier or later than fixation control-trials, depending on when they were presented relative to the saccade. These results explain well the time compression, and also the temporal reversals between two visual stimuli during saccades. The temporal distortions also depended on perceived spatial position. While making temporal judgments, subjects also reported the perceived position of the bar. The magnitude of temporal distortion correlated neither with the physical position of the target, nor with the amount of perceived perisacaddic spatial displacement; instead it correlated well with the perceived vicinity of the position of the stimulus to saccadic targets. All these results reinforce the evidence that the localization of visual events in space and in time are mediated by neurones with craniotopic receptive fields and that these alteration are instrumental in achieving perceptual stability.