Corrective mechanisms of motion extrapolation

Abstract

Transmission and processing of sensory information in the visual system takes time. For motion perception, our brain can overcome this intrinsic neural delay through extrapolation mechanisms and accurately predict the current position of a continuously moving object. But how does the system behave when the motion abruptly changes and the prediction becomes wrong? Here we address this question by studying the perceived position of a moving object with various abrupt motion changes by human observers. We developed a task in which a bar is monotonously moving horizontally, and then motion suddenly stops, reverses, or disappears-then-reverses around two vertical stationary reference lines. Our results showed that participants overestimated the position of the stopping bar but did not perceive an overshoot in the motion reversal condition. When a temporal gap was added at the reverse point, the perceptual overshoot of the end point scaled with the gap durations. Our model suggests that the overestimation of the object position when it disappears is not linear as a function of its speeds but gradually fades out. These results can thus be reconciled in a single process where there is an interplay of the cortical motion prediction mechanisms and the late sensory transient visual inputs.

Figure 1.

Illustration of the motion stop condition. A bar moves horizontally from left to right, toward the fixation point, and suddenly disappears at an azimuth close to the two vertical black reference lines.

Figure 2.

Illustration of the motion reverse condition. A bar moves horizontally from left to right toward the fixation point and suddenly reverses its direction at an azimuth close to the two vertical black reference lines.

Figure 3.

Psychometric functions of one representative subject in the motion stop condition under different contrast (A), speed (B), and luminance (C) conditions. Boxplots of the PSEs of all subjects in the motion stop condition under different contrast (D), speed (E), and luminance (F) conditions. The colored solid line within each box represents the median. The colored square with a black outline represents the mean PSE of each condition. The box represents the interquartile range (IQR) of the data (25% to 75%). The whiskers represent 1.5 × IQR either above the third quartile or below the first quartile. *p < 0.05; # indicates significant PSE shift from 0.

Figure 4.

Psychometric functions of one representative subject in the motion reverse condition under different contrast (A), speed (B), and luminance (C) conditions. Boxplots of the PSEs in the motion reverse condition under different contrast (D), speed (E), and luminance (F) conditions. he colored solid line within each box represents the median. The colored square with a black outline represents the mean PSE of each condition. The box represents the interquartile range (IQR) of the data (25% to 75%). The whiskers represent 1.5 × IQR either above the third quartile or below the first quartile. *p < 0.05; # indicates significant PSE shift from 0.

Figure 5.

Comparison of the mean PSE magnitude of motion stop and reverse under different contrast (A), speed (B), and luminance (C) conditions. Open and filled dots represent the results of motion stop and reverse respectively. Error bars represent standard error. *p < 0.05; **p < 0.01.

Figure 6.

Illustration of the motion gap reverse experiment. A bar moved horizontally from left to right towards the fixation point before disappearing at a position close to the black reference lines. After a temporal gap of 0 to 100 ms, the bar reappeared at the same location but with a reversed motion direction.

Figure 7.

Psychometric functions of one representative subject in the motion gap reverse experiment for different gap durations at 36°/sec (A). The mean PSE at different gap durations for different speeds (B). Boxplots of the PSEs in the motion gap reverse condition at different speeds (C–F). The colored solid line within each box represents the median. The colored square dots with a black outline within each box represent the mean PSE of each condition. The box represents the interquartile range (IQR) of the data (25% to 75%). The whiskers represent 1.5 × IQR either above the third quartile or below the first quartile. PSE, point of subjective equality; *p < 0.05; # indicates a significant PSE shift from 0.

Figure 8.

Model of the overshoot as a function of the gap duration and speed. Continuous lines represent the model fit (R² = 0.6848) with different shades of blue indicating different speeds. Note that the motion stop data is presented as Infinite gap, but fitted with an assigned value of 1000 ms (see Methods). Data are averaged across all subjects.