The time-dependent modulation of saccade amplitude by illusory length reflects a shared representation between perception and action

Are eye movements miscalibrated when the distance to be crossed is misperceived? The two-visual-stream hypothesis proposes that while perception is influenced by visual context and prone to illusions, actions rely on context-independent metrics and should remain unaffected by such distortions. However, saccadic eye movements have been consistently found to be influenced by the Müller-Lyer illusion. This finding is debated, as it could be explained by saccades being attracted toward the figure’s center of gravity rather than a misrepresentation of the length to be covered. To address this, we conducted three experiments (N = 88) between 2022 and 2024 aimed to measured saccade amplitudes along a horizontal line embedded in Müller-Lyer figures carrefully designed to control for the center-of-gravity effects. Results showed that saccade amplitudes were modulated by the Müller-Lyer illusion beyond what could be attributed to changes in center of gravity. Furthermore, the illusion’s effect on saccade amplitude was enhanced following a brief preview duration (50 ms) compared to a longer preview duration (2000 ms). These findings rather support the idea that perception and oculomotor behavior rely on a shared visual representation that is influenced by visual context but becomes more precise with increased processing time.