Abstract
It is reasonable to assume that when we grasp an object we carry out the movement based only on the currently available sensory information. Unfortunately, our senses are often prone to err. Here, we show that the visuomotor system exploits the mismatch between the predicted and sensory outcomes of the immediately preceding action (sensory prediction error) to attain a degree of robustness against the fallibility of our perceptual processes. Participants performed reach-to-grasp movements toward objects presented at eye level at various distances. Grip aperture was affected by the object distance, even though both visual feedback of the hand and haptic feedback were provided. Crucially, grip aperture as well as the trajectory of the hand were systematically influenced also by the immediately preceding action. These results are well predicted by a model that modifies an internal state of the visuomotor system by adjusting the visuomotor mapping based on the sensory prediction errors. In sum, the visuomotor system appears to be in a constant fine-tuning process which makes the generation and control of grasping movements more resistant to interferences caused by our perceptual errors.
Highlights
It is reasonable to assume that when we grasp an object we carry out the movement based only on the currently available sensory information
We propose that the motor system tries to overcome these biased estimates by the trial-by-trial adjustment of a visuomotor mapping based on sensory-prediction errors
It was subject to a lesser degree to biases caused by lack of depth constancy. In both conditions, the grasp relied on a size estimate r, which in first approximation was a linear function of object distance df: r = r + sd(df −
Summary
It is reasonable to assume that when we grasp an object we carry out the movement based only on the currently available sensory information. Grip aperture as well as the trajectory of the hand were systematically influenced by the immediately preceding action These results are well predicted by a model that modifies an internal state of the visuomotor system by adjusting the visuomotor mapping based on the sensory prediction errors. Objects close to the observer are perceived farther and deeper than they are, while objects far from the observer are perceived closer and shallower than they are (Fig. 1a,b) These distortions can be explained with the wrong encoding of distance information from ocular vergence and can be modeled, in first approximation, with a linear function of negative slope relating depth estimates to object distance (Fig. 1c)[11]. We hypothesize that (1) a sensory prediction error is generated after every grasp; (2) the detected error yields a correction of the planned grip aperture We tested this idea in an experimental environment where participants repeatedly grasped the same object. To ensure that biases did not accumulate over time, we counterbalanced the trials using de Bruijn sequences[13]
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