Abstract
Using a trackpad to control an on-screen cursor requires the transformation of proximal finger movements into distal cursor movements displayed within the screen’s allocentric reference frame. Transforming a visually guided action into scene-based coordinates may increase the degree of perceptual influence during a point-and-click task. In this study, the Ebbinghaus illusion was used in three experiments to explore how the perceived size of an on-screen target influences cursor movements and click-point accuracy. Participants completed the experiment remotely, using the trackpad of their personal laptop computers. The task involved a series of trials requiring participants to click on a single circular target presented at either the left or right side of the screen as quickly and accurately as possible (Experiment 1), or to emphasize speed (Experiment 2) or accuracy (Experiment 3). On each trial the target was either surrounded by small or large context circles, or no context circles. Trials presenting veridically smaller or larger targets without context circles were also included for comparison. A size comparison task demonstrated participants’ perceptual size judgments were influenced by the illusory context. However, the illusion failed to produce differences in click-point accuracy or movement time. Interestingly, cursor trajectories demonstrated an increased number of direction changes when clicking the Perceived Large target compared to the Perceived Small target in Experiment 1. This comparison was replicated in Experiment 2, but only when the targets were presented on the right side of the screen. The number of directional changes increased for all target types except for the Perceived Small target in Experiment 3. These results suggest the planning and early stages of cursor movement may have been influenced by the perceptual illusory context while later stages were not, and cursor movements directed toward targets perceived as smaller required less correction compared to targets perceived as larger.