The tilt-constancy theory of visual illusions

The authors argue that changes in the perception of vertical and horizontal caused by local visual cues can account for many classical visual illusions. Because the perception of orientation is influenced more by visual cues than gravity-based cues when the observer is tilted (e.g., S. E. Asch & H. A. Witkin, 1948), the authors predicted that the strength of many visual illusions would increase when observers were tilted 30 degrees. The magnitude of Z?llner, Poggendorff, and Ponzo illusions and the tilt-induction effect substantially increased when observers were tilted. In contrast, the Müller-Lyer illusion and a size constancy illusion, which are not related to orientation perception, were not affected by body orientation. Other theoretical approaches do not predict the obtained pattern of results.     

Geometrical haptic illusions revisited: Haptic illusions compared with visual illusions

Révész (1934) reported that haptic illusions were observed in almost all of the geometrical optical illusion figures. The present study reexamined seven geometrical illusions in both haptic and visual modes. In the Müller-Lyer, Ponzo, and vertical-horizontal figures, haptic illusions equivalent to the visual illusions were observed. In the Oppel-Kundt figure, a haptic illusion similar to the visual one was obtained. In the haptic Delboeuf stimuli, the size illusion of the outer circle occurred, whereas that of the inner circle did not. No haptic illusion was obtained in the Poggendorff figure. In the Zöllner figure, a haptic illusion directionally opposite to the visual one was obtained. These results show that haptic illusions do not occur in all of the geometrical illusion figures. They also suggest that haptic illusions are not necessarily mediated by visualization and that haptic processing of the figures often occurs in a manner different from vision.     

The nature of size scaling in the Ponzo and related illusions

The failure of previous investigators to obtain a Ponzo illusion when each test line is rotated 90 deg from its conventional placement has been interpreted as a refutation of constancy scaling theory. It was proposed that, instead, these results might be due to a failure of linear perspective to elicit foreshortening scaling, and vice versa, since the two types of perspective have different functions. This hypothesis was tested and confirmed.     

Antigravity hills are visual illusions

Antigravity hills, also known as spook hills or magnetic hills, are natural places where cars put into neutral are seen to move uphill on a slightly sloping road, apparently defying the law of gravity. We show that these effects, popularly attributed to gravitational anomalies, are in fact visual illusions. We re-created all the known types of antigravity spots in our laboratory using tabletop models; the number of visible stretches of road, their slant, and the height of the visible horizon were systematically varied in four experiments. We conclude that antigravity-hill effects follow from a misperception of the eye level relative to gravity, caused by the presence of either contextual inclines or a false horizon line.     

On the non-additivity of visual tilt illusions

In Experiment I, the visual tilt illusion induced by two orthogonal lines was found to differ from the sum of the illusions induced by each line independently. The length of one of the orthogonal-inducing lines was varied in Experiment II with the other inducing line remaining a fixed length. As length increased from zero (no line) to 100%, the size of the illusion increased monotonically. The increase in illusion was not due to the increasing length of the variable line alone since, in the absence of the line of fixed length, increasing the length of the variable line produced no significant trend in the illusion (Experiment III).     

Testing the tilt-constancy theory of visual illusions

Prinzmetal and Beck (2001) Journal of Experimental Psychology: Human Perception and Performance 27 206 - 217) argued that a subset of visual illusions is caused by the same mechanisms that are responsible for the perception of vertical and horizontal a theory they referred to as the tilt-constancy theory of visual illusions. They argued that these illusions should increase if the observer's head or head and body are tilted because extra reliance would then be placed on the illusion-inducing local visual context. Exactly that result had previously been reported in the case of the tilted-room and the rod-and-frame illusions. Prinzmetal and Beck reported similar increases in the tilt illusion (TI), as well as the Z?llner, Poggendorff, and Ponzo illusions. In two experiments, we re-examined the effect of head tilt on the TI. In experiment 1, we used more conventional TI stimuli, more standard experimental methods, and a more complete experimental design than Prinzmetal and Beck, and additionally extended the investigation to attraction as well as repulsion effects. Experiment 2 more closely replicated the Prinzmetal and Beck stimuli. Although we found that head tilt did increase TIs in both experiments, the increases were of the order of 1 degrees -2 degrees, more modest than the 7 degrees reported by Prinzmetal and Beck. Significantly, the TI increase was larger when inducing tilts and head tilts were in the same direction than when they were in opposite directions, suggesting that the tilt-constancy theory may be oversimplified. In addition, because previous evidence renders unlikely the claim that the Poggendorff illusion can be explained simply in terms of misperceived orientation of the transversals, the question arises whether there might be some other explanation for the increase in the Z?llner, Poggendorff, and Ponzo illusions with body tilt that Prinzmetal and Beck reported.     

Visual capture in visual illusions

Visual capture is the resolution of visual-tactual conflicts in favor of vision. In each previous demonstration of this phenomenon, a distorted optic array, or some mechanical analog for a distorted optic array, has produced a conflict between erroneous visual information and presumably veridical tactual information. The present experiments demonstrate visual capture in the Müller-Lyer and Ponzo illusions in the absence of any distortions of the optic array.     

Mechanisms for precuing superiority in visual recognition

Superior recognition, when similar alternatives are studied prior to brief target pictures of common objects, is usually attributed to selective feature analysis, which is beneficial only when the target is not readily discriminable in the alternatives. The present study found equal precuing superiority, however, for similar and dissimilar alternatives with abstract geometric stimuli, and with pictures of common objects, precuing superiority occurred only when each alternative represented the same semantic category. Precuing effects did not appear when different categories were represented in the alternatives, and performance was similar to other conditions in which only a categorical match between target and alternatives was possible. These results suggest that selective feature analysis and precuing superiority only occur when the target cannot be identified by its semantic category. With dissimilar alternatives activation of the target's category can be used to select a response, and there is no benefit from precuing.     

An empirical taxonomy of visual illusions

A classification system for visual-geometric illusions, based upon the interrelationships between behavioral responses to various distortions was created. Forty-five illusion configurations were presented to 221 observers. Factor analysis revealed that there are five classes of illusions. A secondorder analysis revealed that visual distortions are ultimately reducible to two global types of distortions: illlusions of extent and illusions of shape or direction.     

Effects of visual illusions on grasping

In 2 experiments, the Muller-Lyer illusion (F. C. Muller-Lyer, 1889; N = 16) and the parallel-lines illusion (W. Wundt, 1898; N = 26) clearly affected maximum preshape aperture in grasping (both ps < .001). The grasping effects were similar but not perfectly equal to the perceptual effects. Control experiments show that these differences can be attributed to problems in matching the perceptual task and the grasping task. A model is described stating the assumptions that are needed to compare the grasping effects and the perceptual effects of visual illusions. Further studies on the relationship between perception and grasping are reviewed. These studies provide no clear evidence for a dissociation between perception and grasping and therefore do not support the action versus perception hypothesis (A. D. Milner & M. A. Goodale, 1995).     

Perceptual illusions in brief visual presentations

We often feel that our perceptual experience is richer than what we can express. For instance, when flashed with a large set of letters, we feel that we can see them all, while we can report only a few. However, the nature of this subjective impression remains highly debated: while many favour a dissociation between two forms of consciousness (access vs. phenomenal consciousness), others contend that the richness of phenomenal experience is a mere illusion. Here we addressed this question with a classical partial-report paradigm now modified to include unexpected items in the unreported parts of the stimuli. We show that even in the presence of unexpected pseudo-letters, participants still felt that there were only letters. Additionally, we show that this feeling reflects an illusion whereby participants reconstruct letters using partial letter-like information. We propose that the feeling of seeing emerges from the interplay between partially accessible information and expectations.     

Voluntary action alters the perception of visual illusions

Attention, Perception, & Psychophysics - “Intentional binding” refers to the finding that people judge voluntary actions and their effects as having occurred closer together in time...     

Action does not resist visual illusions

Recent TICS articles1, 2 discussed the psychophysical evidence in favor of Goodale and Milner's action vs. perception hypothesis³. Carey argued that most of the studies investigating the effects of visual illusions on grasping can be reconciled with the notion that the action system resists visual illusions¹. Bruno suggested a new interpretation of the action vs. perception hypothesis in order to incorporate most of the empirical findings². Here, I argue that action does not resist visual illusions. Even more, the effects on the motor system seem to be comparable to the effects on the perceptual system. This challenges the action vs. perception hypothesis in its current form.     

In defense of the assimilation theory of visual illusions

It is argued that, contrary to Schiano's view (1986), assimilation theory does explain the nonmonotonic relationship between degree of distortion and size of context.     

Contextual illusions reveal the limit of unconscious visual processing

The perception of even the most elementary features of the visual environment depends strongly on their spatial context. In the study reported here, we asked at what level of abstraction such effects require conscious processing of the context. We compared two visual illusions that alter subjective judgments of brightness: the simultaneous brightness contrast illusion, in which two circles of identical physical brightness appear different because of different surround luminance, and the Kanizsa triangle illusion, which occurs when the visual system extrapolates a surface without actual physical stimulation. We used a novel interocular masking technique that allowed us to selectively render only the context invisible. Simultaneous brightness contrast persisted even when the surround was masked from awareness. In contrast, participants did not experience illusory contours when the inducing context was masked. Our findings show that invisible context is resolvable by low-level processes involved in surface-brightness perception, but not by high-level processes that assign surface borders through perceptual completion.     

Evolved navigation theory and horizontal visual illusions

Environmental perception is prerequisite to most vertebrate behavior and its modern investigation initiated the founding of experimental psychology. Navigation costs may affect environmental perception, such as overestimating distances while encumbered (Solomon, 1949). However, little is known about how this occurs in real-world navigation or how it may have evolved. We manipulated the most commonly navigated surfaces with a non-intuitive cost derived from evolved navigation theory. Observers in realistic settings unknowingly overestimated horizontal distances that contained a risk of falling and did so by the relative degree of falling risk. This manipulation produced previously unknown, large magnitude illusions in everyday vision in the environments most commonly navigated by humans. These results bear upon predictions from multiple fundamental theories of visual cognition.     

Integration biases in the Ouchi and other visual illusions

A texture pattern devised by the Japanese artist H Ouchi has attracted wide attention because of the striking appearance of relative motion it evokes. The illusion has been the subject of several recent empirical studies. A new account is presented, along with a simple experimental test, that attributes the illusion to a bias in the way that local motion signals generated at different locations on each element are combined to code element motion. The account is generalised to two spatial illusions, the Judd illusion and the Z?llner illusion (previously considered unrelated to the Ouchi illusion). The notion of integration bias is consistent with recent Bayesian approaches to visual coding, according to which the weight attached to each signal reflects its reliability and likelihood.