Combined visual illusion effects on the perceived index of difficulty and movement outcomes in discrete and continuous fitts’ tapping

Abstract

The speed-accuracy trade-off is a fundamental movement problem that has been extensively investigated. It has been established that the speed at which one can move to tap targets depends on how large the targets are and how far they are apart. These spatial properties of the targets can be quantified by the index of difficulty (ID). Two visual illusions are known to affect the perception of target size and movement amplitude: the Ebbinghaus illusion and Muller-Lyer illusion. We created visual images that combined these two visual illusions to manipulate the perceived ID, and then examined people's visual perception of the targets in illusory context as well as their performance in tapping those targets in both discrete and continuous manners. The findings revealed that the combined visual illusions affected the perceived ID similarly in both discrete and continuous judgment conditions. However, the movement outcomes were affected by the combined visual illusions according to the tapping mode. In discrete tapping, the combined visual illusions affected both movement accuracy and movement amplitude such that the effective ID resembled the perceived ID. In continuous tapping, none of the movement outcomes were affected by the combined visual illusions. Participants tapped the targets with higher speed and accuracy in all visual conditions. Based on these findings, we concluded that distinct visual-motor control mechanisms were responsible for execution of discrete and continuous Fitts' tapping. Although discrete tapping relies on allocentric information (object-centered) to plan for action, continuous tapping relies on egocentric information (self-centered) to control for action. The planning-control model for rapid aiming movements is supported.

Dissociating the Influence of Perceptual Biases and Contextual Artifacts Within Target Configurations During the Planning and Control of Visually Guided Action

“…Once participants were ready to estimate the same perceived size, then they had to press the "return" key in their own time. This unconstrained time accommodates the more prolonged ventrally-mediated perception of relative size differences, which is consistent with previous accounts of a perceptual-matching task involving an illusion (e.g., Alphonsa et al, 2016;2017). The objects were always coloured red and located at diagonals so they could not possibly align the vertical or horizontal boundaries of the target with some external reference (e.g., screen edge).…”

“…To-date, the findings have been rather mixed with aiming movements appearing to be consistent with the Ebbinghaus/Tichener circles illusion when they are executed in the absence of online visual feedback (open-loop) (van Donkelaar, 1999) as opposed to it being present throughout the movement (closed-loop) (Fischer, 2001) (for similar effects within different tasks and illusions, see Elliott & Lee, 1995;Heath, Rival, & Neely, 2006;Meegan et al, 2004;Westwood & Goodale, 2003). Likewise, there is an increased perceptual bias induced by this same illusion when the aiming movements are discrete as opposed to continuous (Alphonsa, Dai, Benham-Deal, & Zhu, 2016;2017; for alternative findings, see Knol, Huys, Sarrazin, Spiegler, & Jirsa, 2017;Skewes, Roepstorff, & Frith, 2011). These discrepancies may be explained by the ventral pathway more greatly contributing toward preresponse, memory-guided aiming movements, while the dorsal pathway primarily contributes to much smoother, visually-regulated aiming movements.…”

Use of remote data collection methodology to test for an illusory effect on visually guided cursor movements

“…Participants therefore had ample opportunity to refine and adjust their movements online to achieve a consistently high level of accuracy. Previous research successfully demonstrating an influence of the Ebbinghaus illusion on visually guided aiming movements has typically involved removal of visual feedback to some degree, either by removing vision of the hand (van Donkelaar, 1999), or the target (Fischer, 2001;Alphonsa et al, 2016). Both the perception-action and planning-control models predict that by removing visual feedback of the target, a greater emphasis will be placed on participants' sensorimotor memory of the target's position, therefore recruiting the perceptual system's involvement in the 10.3389/fpsyg.2022.922381 task, and increasing the likelihood of an illusory influence.…”

“…The extent to which the Ebbinghaus illusion influences the precision and timing of other visually guided actions such as pointing or tapping has also been explored (van Donkelaar, 1999;Handlovsky et al, 2004;Alphonsa et al, 2016;Knol et al, 2017). Instead of requiring an appropriately scaled grasp matched to the boundaries of a circular target object, these actions require performing an accurate movement toward the target's center, and the influence of the illusion is typically investigated by testing for the presence of a speed-accuracy trade-off (e.g., Fitts' Law;Fitts, 1954), when acting on targets perceived to be smaller or larger than their veridical size.…”

“…A critical difference between the early van Donkelaar (1999) and later Fischer (2001) studies involved visibility of the hand: participants in van Donkelaar's original study did not have visual feedback of their hand, while those in Fischer's later study were able to see their hand while performing the task. In a similar study, Alphonsa et al (2016) adapted a typical Fitts tapping task to include qualities of both the Ebbinghaus and the Muller-Lyer illusions. Despite the physical size and distance of the two target stimuli being identical, participants were more accurate when tapping targets in the "illusory easy" condition, in which the combination of illusions increased the perceived size of the target.…”