关键词: 扫视, 时间压缩, 时序倒置, 时间膨胀

Abstract: Saccadic eye-movement is a kind of rapid eye movement moving from one fixation to another, which can bring visual stimuli into fovea. However, the image on the retina moves at a speed of hundred degrees per second during a saccade, which distorts the visual time perception, leading to phenomena such as time compression, temporal order reversal and temporal dilation, etc. During fixation and well before or after saccades, time perception remains veridical. However, perisaccadic visual (rather than auditory) short intervals will be underestimated. Specifically, when visual intervals presented close to saccadic onset (e.g. -50 to 50 ms), the subjective interval between two visual stimuli is strongly compressed to approximately half of its true value. Surprisingly, perceived visual temporal order is reversed in a critical window before the saccade onset. This phenomenon is called “temporal order reversal”. In addition to the distortions mentioned above, saccades can also induce “chronostasis” (stopped clock illusion). Saccadic chronostasis demonstrates the subjective overestimation of stimulus duration when the stimulus onset surrounds the offset of a saccade. In our daily life, when we make a saccade to a clock, the first second seems always “longer” than the subsequent seconds. According to the previous studies, time compression and temporal order reversal may be caused by reduced-latency, errors of temporal encoding, and predictive remapping. When the second stimulus which marks the offset of the interval presented shortly before or after saccade onset, its latency is shorter than normal conditions. At the same time, the first stimulus which marks the onset of the interval remains stable. Thus, the temporal order of two stimuli will be reversed. However, the reduced-latency theory cannot fit well with the “time compression” phenomenon. Some researchers suggest that time compression may concern the reduced-contrast which derives from the errors of temporal encoding. At the single-cell level, cells can respond to stimuli presented within spatial positions that will become their receptive field after the saccades. This process is mediated by a corollary discharge signal (CDS). The predictive shift of receptive field enables the representation of visual space in parietal cortex to be remapped from the coordinates of the initial fixation to those of the future fixation. This alternative interpretation names “predictive remapping”. Because of predictive remapping, the stimuli within future receptive fields have longer latencies. When the first stimulus which marks the onset of the interval is presented perisaccadically and the second marker flashes well after the saccades, the interval between two markers compressed. Temporal dilation may derive from perceptual antedating of stimuli that surround the saccade target. When we make saccades, saccadic suppression leaves a perceptual “gap” in perception. However, the perception of visual space remains continuous and stable despite saccades. The brain assumes that the post-saccadic stimuli remain constant during the saccades and brings the onset of stimuli after saccades to the time point prior to the saccades. This interpretation supports the conclusion that the overestimation of stimuli duration will increase with the amplitude (duration) of saccades. And when the target shifts during the saccades, no temporal dilation observed. However, if participants do not notice the displacement, the duration of stimuli will still be overestimated. That is, if the assumption of continuous awareness is incorrect, the onset of stimulus will not be antedated and thus chronostasis will disappear. The investigation on visual stimuli processing under saccades will be of great benefit to explore the natural temporal property of the brain networks. Further research can focus on the visual coordinates to investigate the relationship of different distortions. Also, researchers can discriminate different saccadic steps to identify the contribution of predictive remapping and saccadic suppression. So that researchers will modify the computational models of predictive remapping.

Key words: Saccades, Time compression, Temporal order reversal, Temporal dilation