Dynamic illusory size contrast: A relative-size illusion modulated by stimulus motion and eye movements

Abstract

We present a novel size-contrast illusion that depends on the dynamic nature of the stimulus. In the dynamic illusory size-contrast (DISC) effect, the viewer perceives the size of a target bar to be shrinking when it is surrounded by an expanding box and when there are additional dynamic cues such as eye movements, changes in retinal eccentricity of the bar, or changes in the spatial position of the bar. Importantly, the expanding box was necessary but not sufficient to obtain an illusory percept, distinguishing the DISC effect from other size-contrast illusions. We propose that the visual system is weighting the different sources of information that contribute to size perception based on the level of uncertainty in the retinal image size of the object. Whereas the growing box normally has a weak influence on the perceived size of the target bar, this influence is enhanced when other dynamic changes in the environment (e.g., eye movements, changes in retinal eccentricity, and target motion) lead to uncertainty in the retinal size of the target bar. Given the compelling nature of the DISC effect and the inherently dynamic nature of our environment, these factors are likely to play an important role in everyday size judgments.

The Dynamic Ebbinghaus: motion dynamics greatly enhance the classic contextual size illusion

“…In stark contrast, adding target motion by having the entire stimulus translate across the screen led to an illusory effect size (~37%, Dynamic-Moving condition) that was almost twice that of the classic static Ebbinghaus. It is this huge discrepancy between the Stationary and Moving dynamic conditions, also replicated in Experiment 2 (~5 vs. ~35%), that exemplifies what we have previously termed the Dynamic Illusory Size Contrast (DISC) effect (Mruczek et al, 2014 ). By itself, a dynamic change in the inducers is insufficient for strongly biasing perception.…”

“…The Dynamic Ebbinghaus illusion shows that the DISC effect is not limited to the particular stimulus configuration we originally used to demonstrate the effect (a target bar surrounded by an expanding square box, Figure 2 ; Mruczek et al, 2014 ). Additionally, the direct comparison between the Static and Dynamic illusions (Experiment 1) shows that the subjectively strong nature of the dynamic illusion can be empirically quantified.…”

“…Previously, we proposed an information uncertainty hypothesis to account for the DISC effect (Mruczek et al, 2014 ). Perceived size is the result of the integration of multiple visual cues, including retinal image size, perceived distance, and other contextual effects such as relative size and contour interactions.…”

“…We recently introduced a novel illusion called the Dynamic Illusory Size-Contrast (DISC) effect, which highlights the role of dynamic visual information in modulating the contribution of different sources of information in determining the perceived size of an object (Mruczek et al, 2014 ). In the DISC effect, the viewer perceives the size of a target bar to be shrinking when (1) it is surrounded by an expanding box and (2) there are additional dynamic cues such as eyes movements or bar motion (Figure 2 ).…”

“…We previously proposed that the dynamic nature of the DISC stimulus leads to greater uncertainty regarding the image size of the target object because of motion-related noise at the level of the retinal input. As a result, other sources of information, such as relative size, contribute more to its perceived size, thereby greatly increasing the magnitude of the illusory percept (Mruczek et al, 2014 ). The information uncertainty hypothesis suggests that the DISC effect should not be limited to the specific stimulus we originally examined.…”