Effects of smooth pursuit and second-order stimuli on visual motion prediction

The effect of eccentricity on visual motion prediction in peripheral vision

The purpose of the current study was to clarify the effect of eccentricity on visual motion prediction using a time-to-contact (TTC) task. TTC indicates the predictive ability to accurately estimate the time-to-contact of a moving object based on visual motion perception. We also measured motion reaction time (motion RT) as an indicator of the speed of visual motion perception. The TTC task was to press a button when the moving target would arrive at the stationary goal. In the occluded condition, the target dot was occluded 500 ms before the time to contact. The motion RT task was to press a button as soon as the target moved. The visual targets were randomly presented at five different eccentricities (4°, 6°, 8°, 10°, 12°) and moved on a circular trajectory at a constant tangent velocity (8°/s) to keep the eccentricity constant. Our results showed that TTC in the occluded condition showed an earlier response as the eccentricity increased. Furthermore, the motion RT became longer as the eccentricity increased. Therefore, it is most likely that a slower speed perception in peripheral vision delays the perceived speed of motion onset and leads to an earlier response in the TTC task.

Changes in visual speed perception induced by anticipatory smooth eye movements

Expectations about forthcoming visual motion shaped by observers' experiences are known to induce anticipatory smooth eye movements (ASEM) and changes in visual perception. Previous studies have demonstrated discrete effects of expectations on the control of ASEM and perception. However, the tasks designed in these studies were not able to segregate the effects of expectations and execution of ASEM itself on perception. In the current study, we attempted to directly examine the effect of ASEM itself on visual speed perception using a two-alternative forced-choice task (2AFC task), in which observers were asked to track a pair of sequentially presented visual motion stimuli with their eyes and to judge whether the second stimulus (test stimulus) was faster or slower than the first (reference stimulus). Our results showed that observers' visual speed perception, quantified by a psychometric function, shifted according to ASEM velocity. This was the case, even though there was no difference in the steady-state eye velocity. Further analyses revealed that the observers' perceptual decisions could be explained by a difference in the magnitude of retinal slip velocity in the initial phase of ocular tracking when the reference and test stimuli were presented, rather than in the steady-state phase. Our results provide psychophysical evidence of the importance of initial ocular tracking in visual speed perception and the strong impact of ASEM.

The effect of explicit cues on smooth pursuit termination

Predictive deceleration of eye motion during smooth pursuit is induced by explicit cues indicating the timing of the visual target offset. The first aim of this study (experiment 1) was to determine whether the timing of the onset of cue-based predictive pursuit termination depends on spatial or temporal information using three target velocities. The second aim (experiment 2) was to examine whether an unexpected offset of the target affects the pursuit termination. We conducted a pursuit termination task where participants tracked a moving target and then stopped tracking after the target disappeared. The results of experiment 1 showed that the onset times of predictive eye deceleration were consistent regardless of target velocity, indicating that its timing is controlled by the temporal estimation, rather than the spatial distance between the target and cue positions. In experiment 2, we compared pursuit termination between the following two conditions. One condition did not present any cues (unknown condition), whereas a second condition included a same cue as experiment 1 but the target disappeared 500 ms before the timing indicated by the cue unpredictably (unexpected condition). As a result, the unexpected condition showed significant delays in the onset of eye deceleration, but no difference in the total time for completion of pursuit termination. Therefore, our findings suggest that the cue-based pursuit termination is controlled by the predictive pursuit system, and an unexpected offset of the target yields delays in the onset of eye deceleration, while does not affect the duration of pursuit termination.