Adaptation effects in grasping the Müller-Lyer illusion

Abstract

Recent results have shown that effects of pictorial illusions in grasping may decrease over the course of an experiment. This can be explained as an effect of sensorimotor learning if we consider a pictorial size illusion as simply a perturbation of visually perceived size. However, some studies have reported very constant illusion effects over trials. In the present paper, we apply an error-correction model of adaptation to experimental data of N=40 participants grasping the Müller-Lyer illusion. Specifically, participants grasped targets embedded in incremental and decremental Müller-Lyer illusion displays in (1) the same block in pseudo-randomised order, and (2) separate blocks of only one type of illusion each. Consistent with predictions of our model, we found an effect of interference between the two types when they were presented intermixed, explaining why adaptation rates may vary depending on the experimental design. We also systematically varied the number of object sizes per block, which turned out to have no effect on the rate of adaptation. This was also in accordance with our model. We discuss implications for the illusion literature, and lay out how error-correction models can explain perception-action dissociations in some, but not all grasping-of-illusion paradigms in a parsimonious and plausible way, without assuming different illusion effects.

The endless visuomotor calibration of reach-to-grasp actions

“…Note that this error is not what we claim to be actually measured by the visuomotor system. We simply assume that this quantity is linearly related to the discrepancy between the expected kinematics of the movement and those experienced through proprioception 19 – 21 . For example, if the planned grasp is too large ( ), the fingers will touch the object later than expected.…”

“…The exact same reasoning can be applied to account for the failure in learning the optimal way to transport the hand toward the object. The visuomotor mapping was constantly updated with conflicting information and, therefore, the error corrections simply neutralized one another 19 – 21 .…”

Stereovision for action reflects our perceptual experience of distance and depth

“…If the systematic biases observed in Experiments 1 and 2 are not due to the absence of visuo-haptic feedback, then they should be observed under these conditions too. Moreover, the discrepancy between the estimated depth of the grasped object, which is biased at planning, and the felt size of the object, should produce systematic error corrections, as predicted by what we define as the sensorimotor correction hypothesis (Kopiske, Cesanek, Campagnoli, & Domini, 2017).…”

A review of grasping as the movements of digits in space

“…If one misjudges the size of an object that one is reaching to grasp, one will have a peculiar velocity profile just before contact (as discussed in the previous paragraph), but one will also use this error to update one's movement plan for the next movement toward the same object Kopiske et al 2017). Such updating illustrates the effect of errors in previous trials on reaching to grasp, in line with the literature on pointing (van Beers 2009), interception (de Lussanet et al 2001), and the control of grip force (Westling and Johansson 1984).…”