Imposed visual feedback delay of an action changes mass perception based on the sensory prediction error

Abstract

While performing an action, the timing of when the sensory feedback is given can be used to establish the causal link between the action and its consequence. It has been shown that delaying the visual feedback while carrying an object makes people feel the mass of the object to be greater, suggesting that the feedback timing can also impact the perceived quality of an external object. In this study, we investigated the origin of the feedback timing information that influences the mass perception of the external object. Participants made a straight reaching movement while holding a manipulandum. The movement of the manipulandum was presented as a cursor movement on a monitor. In Experiment 1, various delays were imposed between the actual trajectory and the cursor movement. The participants' perceived mass of the manipulandum significantly increased as the delay increased to 400 ms, but this gain did not reach significance when the delay was 800 ms. This suggests the existence of a temporal tuning mechanism for incorporating the visual feedback into the perception of mass. In Experiment 2, we examined whether the increased mass perception during the visual delay was due to the prediction error of the visual consequence of an action or to the actual delay of the feedback itself. After the participants adapted to the feedback delay, the perceived mass of the object became lighter than before, indicating that updating the temporal prediction model for the visual consequence diminishes the overestimation of the object's mass. We propose that the misattribution of the visual delay into mass perception is induced by the sensorimotor prediction error, possibly when the amount of delay (error) is within the range that can reasonably include the consequence of an action.

Keywords: delay adaptation; feedback delay; mass perception; prediction error; sensorimotor prediction.

Figure 1

Top-down view of twin visuomotor and haptic interface system (TVINS). In Experiment 1, only the right-hand manipulandum was used. In Experiment 2, both manipulanda were used. The horizontal screen is illustrated as if it were transparent in order to show the manipulandum. In reality, it was opaque and reflected images generated by the projector installed above.

Figure 2

Two types of trials in Experiment 2. The horizontal flow is the sequence of each trial; (A) Delay awareness trial in which subjects were asked if they felt any delay in cursor movements, and (B) mass comparison trials in which subjects were asked to judge whether the right- or left-hand movement was heavier. The instruction was on the screen from the end of the last trial until the onset of the next trial (target appearance). The yellow letters and arrows are used to explain each display, but they are not shown on the screen during the actual experiment.

Figure 3

Results of Experiment 1. (A) Results are shown for a typical participant. The mass value at which each curve crosses the 0.5 line is PSE for each delay value. The red arrow indicates the shift of PSE for a 800-ms delay from that for a 0-ms delay (see panel C). (B) Psychometric functions are fitted to data averaged across participants. Average judgment rate across participants was calculated for each mass value, and sigmoid functions were fitted to the averaged rates. (C) For each delay, the shift of PSE from that for a 0-ms delay is shown. Shifts were calculated for each cursor delay and averaged across participants. Error bars indicate standard error of measures across participants. *p < 0.05 according to Ryan's multiple (four) comparison tests for difference in PSE between 0-ms delay and the other delay conditions.

Figure 4

Results of Experiment 2. (A) Average delay awareness across participants is shown in each condition. *p < 0.05 according to the paired t-test. (B) Rate of the delay awareness is shown as a function of block number. (C) Average judgment of “right hand heavier” across participants is shown for each right-hand mass value in each condition. Error bars indicate standard error of measures across participants.