A new theory to explain geometrical illusions produced by crossing lines

Due to the diffraction of light and other optical distortions of the eye, the image of an object is not exactly the same as the object. When two objects are close enough, their two images overlap so as to form one image, located at a position somewhere between the two original images. This fact is used to explain illusions produced by the crossing of lines, including Poggendorffs, Zollner’s, Hering’s, Wundt’s, the Müller-Lyer and other illusions of this class.     

Illusory illusions: the significance of fixation on the perception of geometrical illusions

Some well-known geometrical illusions disappear when the eyes are fixating and saccades are suppressed for a period of time. This disappearance is not accompanied by fading due to stabilisation of the retinal image. Any saccade made on purpose restores the illusion immediately. The fixation time after which some illusions disappeared was measured for four illusions and four subjects each. Effects of practice have been observed after measurements were repeated on successive days. Present theories of vision cannot readily explain the effect.     

Latency correction explains the classical geometrical illusions

There is a significant delay between the time when light hits the retina and the time of the consequent percept. It has been hypothesized that the visual system attempts to correct for this latency by generating a percept representative of the way the world probably is at the time the percept is elicited, rather than a percept of the recent past. Here we show that such a 'perceiving the present' hypothesis explains a number of classical geometrical illusions: the Hering, Orbison, Müller-Lyer, Double Judd, Poggendorff, Corner, and Upside-down-T illusions. Each stimulus is perceived as it would project in the next moment were the observer moving through the scene the stimulus probably represents. We also examine one general class of predictions made by the hypothesis, and report psychophysical experiments confirming the predictions.     

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.     

A mathematical theory of optical illusions and figural aftereffects

If it is assumed that spurious enhancement of receptive field excitations near the intersection of image lines on the retina contributes to the cortical determination of the geometry of two-dimensional figures, an equation based on the least-squares fit of data points to a straight line-can be obtained to represent theapparent line. Such a fit serves as anextreemum on the precision with which a data set can be represented by a straight line. The disparity between theapparent line and the actual line that occurs in the case of peripheral (and to a lesser degree in more central regions of the retina) vision is sufficient to produce the perceptual errors that occur in the Poggendorff, Hering, and Mueller-Lyer illusions. The magnitude of the Poggendorff illusion as a function of the line angle is derived and experimentally tested. Blakemore, Carpenter, and Georgeson’s (1970) experimental data on angle perception are shown to fit this same function. Theapparent curve is derived for the Hering illusion. The Mueller-Lyer illusion is found to be a variation of the Poggendorff illusion. The equations are further developed and used to derive Pollack’s (1958) experimental results on figural aftereffects. The results involve onlyone experimentally determined coefficient that can be evaluated, within the limits of experimental error, in terms of physiological data. The use of these concepts provides a foundation for the abstract modeling of the initial phases of the central nervous system data reduction processes, including receptive field structure, that is consistent with the physiological limitations of the retina as a source of visual data, as well as with the findings of Hubel and Wiesel (1962).     

Orientation and alignment misjudgement: new geometrical optical illusions?

Misjudgement of orientation is demonstrated in drawings of tilted quadrangles with parallel diagonals. Apparent misalignment of apices and/or line-segment ends is shown in drawings of differently oriented rectangle, angles, and line segments.     

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.     

Assimilation and contrast in geometrical illusions: a theoretical analysis.

It is argued that an unwarranted dichotomization of geometrical illusions has produced theories whose explanatory scope is limited to either assimilation or contrast. Since recent attempts at integration lack precision, a 1977 unified model of the perception of extent by Brigner was revised to predict accurately both assimilative and contrastive phases of the parallel lines illusion. Application of the revised model to other geometrical illusions was discussed and a means of parsimoniously accounting for variations in assimilative illusions occurring with age and with lightness of the stimulus figure was suggested.     

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.     

Traditional rationality vs. a tradition of criticism: A criticism of Popper's theory of the objectivity of science

This essay points out that Popper's theory of the objectivity of science is ambiguous: it is not clear whether it provides a guarantee of correct evaluations of theories or only a means of uncovering errors in such evaluations. The latter approach seems to be a more natural extension of Popper's fallibilist theory and is needed if his learning theory is adopted. But this leads to serious problems for a fallibilist theory of science.     

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.