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

A motion-induced position shift that depends on motion both before and after the test probe

Two versions of the flash grab illusion were used to examine the relative contributions of motion before and motion after the test flash to the illusory position shift. The stimulus in the first two experiments was a square pattern that expanded and contracted with an outline square flashed each time the motion reversed producing a dramatic difference in perceived size between the two reversals. Experiment 1 showed a strong illusion when motion was present before and after the flashed tests or just after the flashes, but no significant effect when only the pre-flash motion was present. In Experiment 2, motion always followed the flash, and the duration of the pre-flash motion was varied. The results showed a significant increase in illusion strength with the duration of pre-flash motion and the effect of the pre-flash motion was almost 50% that of the post-flash motion. Finally, Experiment 3 tested the position shifts when the linear motion of a disk before the flash was orthogonal to its motion after the flash. Here, the results again showed that the pre-flash motion made a significant contribution, about 32% that of the post-flash motion. Several models are considered and even though all fail to some degree, they do offer insights into the nature of the illusion. Finally, we show that the empirical measure of the relative contribution of motion before and after the flash can be used to distinguish the mechanisms underlying different illusions.

The combination of target motion and dynamic changes in context greatly enhance visual size illusions

Perceived size is a function of viewing distance, retinal images size, and various contextual cues such as linear perspective and the size and location of neighboring objects. Recently, we demonstrated that illusion magnitudes of classic visual size illusions may be greatly enhanced or reduced by adding dynamic elements. Specifically, a dynamic version of the Ebbinghaus illusion (classically considered a “size contrast” illusion) led to a greatly enhanced illusory effect, whereas a dynamic version of the Corridor illusion (a “size constancy” illusion) led to a greatly diminished illusory effect. Although these differences may arise from the different processes underlying these illusions (size contrast vs. size constancy), the dynamic variants we tested in our previous work also differed in the nature of the dynamic elements; specifically, whereas the Dynamic Ebbinghaus included a moving target and inducers that changed size and position, the Dynamic Corridor only included a moving target on a static background. Here, we explore further dynamic versions of the Ebbinghaus illusion and the Corridor and Ponzo illusions by separately manipulating three types of dynamic elements: target motion, context translation, and dynamic changes in context. Across five experiments examining 21 dynamic illusory configurations, adding target motion or a dynamically changing context separately resulted in little-to-no illusory effect. In contrast, the combination of target motion and a dynamically changing context led to a robust size illusion, consistent with an interactive effect. However, illusory effects that exceeded the matched classic, static illusory configuration were only observed for the dynamic versions of the Ebbinghaus illusion and the Revealed Ponzo illusions, in which the contextual elements changed size. We conclude that the combination of target motion and a dynamically changing context are necessary to produce dynamic size illusions, but that enhancement above and beyond static illusions may be largely specific to size contrast effects. Our results have important implications for the integration of motion signals, a ubiquitous environmental stimulus, in the perception of object size.

Dynamic presentation boosts the Ebbinghaus illusion but reduces the Müller-Lyer and orientation contrast illusions

Mruczek et al. (2015) showed that a moving version of the Ebbinghaus illusion almost doubles in strength compared to the standard version. In their stimulus, the size of the surrounding inducers was modulated between large and small and the whole stimulus was made to drift during the surround modulation. We first replicated the original dynamic Ebbinghaus illusion and then explored dynamic presentations for other simultaneous contrast and geometric illusions. We found no increase in illusion strength in any that we sampled. Here we report the results for the Müller-Lyer illusion and the orientation contrast illusion. Surprisingly, when these two illusions were presented dynamically, their effects were greatly reduced for the Müller-Lyer illusion and eliminated for the orientation contrast illusion.

Opposite effects of motion dynamics on the Ebbinghaus and corridor illusions

We recently showed that motion dynamics greatly enhance the magnitude of certain size contrast illusions, such as the Ebbinghaus and Delboeuf illusions. Here, we extend our study of the effect of motion dynamics on size illusions through a novel dynamic corridor illusion, in which a single target translates along a corridor background. Across three psychophysical experiments, we quantify the effects of stimulus dynamics on the Ebbinghaus and corridor illusions across different viewing conditions. The results revealed that stimulus dynamics had opposite effects on these different classes of size illusions. Whereas dynamic motion enhanced the magnitude of the Ebbinghaus illusion, it attenuated the magnitude the corridor illusion. Our results highlight precision-driven weighting of visual cues by neural circuits computing perceived object size. This hypothesis is consistent with observations beyond size perception and may represent a more general principle of cue integration in the visual system.

Ebbinghaus visual illusion: no robust influence on novice golf-putting performance

Do visual illusions reliably improve sports performance? To address this issue, we used procedures inspired by Witt et al. (Psychol Sci 23:397-399, 2012) seminal study, which reported that putting on a miniature golf course was positively influenced by an increase in apparent hole size induced by the Ebbinghaus visual illusion. Because Witt et al.'s motor task-putting golf balls toward a hole from the distance of 3.5 m-was impossible for participants who were novices in golf (Experiment 1a), we decided to shorten the putting distance (i.e., 2 m instead of 3.5 m) in Experiment 1b. Otherwise, this second experiment closely followed every other aspects of Witt et al.'s procedure (i.e., one small or one standard golf hole surrounded by a ring of small or large circles). However, this attempt to replicate Witt et al.'s findings failed: the Ebbinghaus illusion significantly influenced neither hole perception nor putting performance. In two subsequent experiments, we encouraged the emergence of the effect of the illusion by simultaneously presenting both versions of the illusion on the mat. This major adaptation successfully modified the perceived size of the hole but had no impact on putting performance (Experiment 2), even when the putting task was made easier by shortening the putting distance to only 1 m (Experiment 3). In the absence of detectable effects of the illusion on putting performance, we conclude that the effects of visual illusions on novice sports performance do not represent a robust phenomenon.

Cross-modal size-contrast illusion: Acoustic increases in intensity and bandwidth modulate haptic representation of object size

Changes in the retinal size of stationary objects provide a cue to the observer's motion in the environment: Increases indicate the observer's forward motion, and decreases backward motion. In this study, a series of images each comprising a pair of pine-tree figures were translated into auditory modality using sensory substitution software. Resulting auditory stimuli were presented in an ascending sequence (i.e. increasing in intensity and bandwidth compatible with forward motion), descending sequence (i.e. decreasing in intensity and bandwidth compatible with backward motion), or in a scrambled order. During the presentation of stimuli, blindfolded participants estimated the lengths of wooden sticks by haptics. Results showed that those exposed to the stimuli compatible with forward motion underestimated the lengths of the sticks. This consistent underestimation may share some aspects with visual size-contrast effects such as the Ebbinghaus illusion. In contrast, participants in the other two conditions did not show such magnitude of error in size estimation; which is consistent with the "adaptive perceptual bias" towards acoustic increases in intensity and bandwidth. In sum, we report a novel cross-modal size-contrast illusion, which reveals that auditory motion cues compatible with listeners' forward motion modulate haptic representations of object size.

Urbanisation, the arousal system, and covert and overt attentional selection

Urbanisation is growing rapidly. We review evidence that this growth is altering the default information processing style of human beings by impacting both overt and covert processes of attentional selection (i.e. attentional selection with and without eye movements respectively), in ways consistent with reduced attentional engagement and increased exploration. While the factors and systems mediating these effects are likely to be many and various, we focus on one system which may be responsible for mediating effects on both covert and overt attentional selection. Specifically, the neuromodulatory locus coeruleus-norepinephrine (LC-NE) system is key to regulating cognitive function in a behaviourally relevant and arousal-dependent manner and therefore well suited to supporting adaptation to the profound socio-ecological changes inherent in urbanisation.

Is the Ebbinghaus illusion a size contrast illusion?

The Ebbinghaus illusion, in which a central target surrounded by larger context figures looks smaller than when surrounded by smaller context figures, is usually classified as a size contrast illusion. Thus "size contrast" is the dominant account of this effect. However, according to an alternative "contour interaction" account this phenomenon has little to do with size contrast but is rather caused by distance-dependent attractive and repulsive interactions between neural representation of contours. Here evidence is presented against the size contrast account and consistent with the contour interaction account. Experiment 1 was a control study confirming that the illusion can be obtained using displays consisting only of squares, which are more convenient to manipulate than the standardly used circles. In Experiment 2, the standard configuration involving small context figures surrounding the target was compared to a novel configuration, which involved many "spread" small context figures. The illusory effect of the standard context was stronger than the illusory effect of the spread context, in accord with the prediction of the contour interaction account, and contrary to the prediction of the size contrast account. In Experiment 3 two novel configurations were used, based on standard and spread contexts. The results were in accord with the prediction of the contour interaction account, whereas the size contrast account had no prediction because the stimuli did not involve conventional size contrast. Additional aspects of the stimuli and an account of the illusion based on a perspective interpretation are also discussed.