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While domestic dogs (Canis familiaris) play a large role in human daily lives, little is known about how they perceive the visual world. Recent research suggests that dogs may perceive certain visual illusions differently than humans. To further evaluate geometric illusion susceptibility, eight dogs were assessed on their susceptibility to the Ponzo illusion. Four experiments were conducted: 1) a presentation of the Ponzo illusion with target circles in a ‘grid inducer context’, 2) a re-test of Experiment 1 after additional training, 3) a presentation of the Ponzo illusion with target rectangles in a ‘grid inducer context’ and 4) a presentation of the Ponzo illusion with target circles in a ‘converging lines context.’ A one-sample t-test of the dogs’ responses to the Ponzo stimuli in Experiment 1 demonstrated illusion susceptibility at the group level; however, no individual dog performed significantly above chance in binomial tests. In Experiments 2, 3, and 4, one-sample t-tests found no significant results at the group level, although one or more dogs did demonstrate a small but significant effect. Taken together, then, there was limited evidence for dogs’ susceptibility to the Ponzo illusion in a two-choice discrimination paradigm. As most animals tested previously have demonstrated human-like susceptibility to the Ponzo illusion, these findings have implications for theoretical explanations. The divergence of results between dogs and humans/other animals suggest that mechanisms underlying perception of the Ponzo illusion may differ across species and that care should be taken when using visual paradigms to test dogs’ cognitive skills.

As a novel and unique visual form, visual illusion enriches the visual perception of the audience with its vivid and interesting visual charm from beginning to end. “Monument Valley” a large number of the use of visual illusion principle, in which perspective illusion, geometric illusion and light and dark illusion for players to bring a different visual experience, combined with the game picture of the unit object scattered reconstruction, the application of visual illusion in this game has jumped.

A disk surrounded by smaller disks looks larger, and one surrounded by larger disks looks smaller than reality. This visual illusion, called the Ebbinghaus-Titchener illusion, remains one of the strongest and most robust illusions induced by contrast with the surrounding stimuli in humans. In the present study, we asked whether bantams would perceive this illusion. We trained three bantams to classify six diameters of target disks surrounded by inducer disks of a constant diameter into "small" or "large". In the test that followed, the diameters of the inducer disks were systematically changed. The results showed that the Ebbinghaus-Titchener figures also induce a strong illusion in bantams, but in the other direction, that is, bantams perceive a target disk surrounded by smaller disks to be smaller than it really is and vice versa. Possible confounding factors, such as the gap between target disk and inducer disks and the weighted sum of surface of these figural elements, could not account for the subjects' biased responses. Taken together with the pigeon study by Nakamura et al. (J Exp Psychol Anim Behav Process 34:375-387 2008), these results show that bantams as well as pigeons perceive an illusion induced by assimilation effects, not by contrast ones, for the Ebbinghaus-Titchener types of illusory figures. Perhaps perceptual processes underlying such illusory perception (i.e., lack of contrast effects) shown in bantams and pigeons may be partly shared among other avian species.

International audience; In our previous studies, we have shown that the occurrence of geometric illusions was reduced in vestibular patients who presented signs of otolith disorders and when healthy observers were tilted relative to gravity. We hypothesized that the alteration in the gravitational (otolith) input was responsible for this change, presumably because of a connection between vestibular and visual-spatial cognitive functions. In this study, we repeated similar experiments in astronauts during long-duration spaceflight. In agreement with the data of otolithic patients, the inverted-T geometric illusion was less present in the astronauts in 0g than in 1g. In addition, the vertical length of drawings made by astronauts in orbit was shorter than that on the ground. This result is also comparable with the otolithic patients who perceived the vertical length of line drawings to be smaller than healthy individuals. We conclude that the impairment in the processing of gravitational input in long-duration astronauts affects their mental representation of the vertical dimension similar to the otolithic patients. The astronauts, however, recover to baseline levels within 1 week after returning to Earth.

Although pigeons have been shown to be susceptible to several size and length illusions, other avian species have not been tested intensively for illusory perception. Here we report how bantams perceive the Zöllner figure, in which parallel lines look nonparallel due to short crosshatches superimposed on the lines. Watanabe et al. (Cognition 119:137-141, 2011) showed that pigeons, like humans, perceived parallel lines as nonparallel but that the orientation of subjective convergence was opposite to that of humans. We trained three bantams to peck at the narrower (or wider) of the two gaps at the end of a pair of nonparallel lines. After adapting them to target lines with randomly oriented crosshatches (which result in no apparent illusion to humans), we tested the bantams' responses on randomly inserted probe trials, in which crosshatches that should induce the standard Zöllner-like illusion for humans replaced the randomly oriented ones. The results suggested bantams, like pigeons, perceive a reversed Zöllner illusion.

The Ebbinghaus illusion is a geometric illusion based on a size-contrast between a central circle and surrounding circles. A central circle surrounded by small inducing circles is perceived as being larger than a central circle surrounded by large inducing circles. In the present study we investigated 5- to 8-month-old infants' perception of the Ebbinghaus illusion using a preferential-looking paradigm. We measured the preference between a central circle surrounded by small inducing circles (overestimated figure) and a central circle surrounded by large inducing circles (underestimated figure). Infants showed a significant preference for the overestimated figure when the central circle was flashing, but not when it was static. Furthermore, there was no preference between the two figures when the central circles were removed. These results suggest that infants' preference reflects their perception of the size illusion of the central circle. There is a possibility that 5- to 8-month-old infants perceive the Ebbinghaus illusion.

Interest in geometric illusions in architectural design was restimulated in the 1970s by the publication of a paper by Gregory and Heard on the Café Wall illusion. Illusory patterns have been used in urban design for centuries. This brief note identifies two further examples of urban illusions found in Alicante, Spain and suggests that they may represent currently the longest examples of urban geometric illusion in the world.

We report two experiments indicating that varying the configuration of face features changes perception of an oval aperture windowing the face: as the eyes and mouth of a frontal-view face photograph are moved vertically toward face boundaries, the oval appears increasingly elongated, taller, and narrower; when eyes and mouth are moved toward the nose, the oval appears increasingly rounder, shorter, and wider. This shape illusion is maximised when faces appear upright within the oval, and major face features (eyes, nose, and mouth) appear in their correct relative locations. These results establish that processing of a face configuration can affect perception of a geometric shape that shares visual space with a face. Whether the illusion is face-specific or a special case of a more general geometric illusion is discussed.

Angular induction is the process by which one line segment can bias judgment of orientation and/or collinearity of another segment, and it has been established that the magnitude of error is a determinate function of the relative angle between the two. We examined how these known relationships are affected by decomposing the induction segment into an array of scattered points. The bias that was produced by such arrays was found to be consistent with a formal model of angular induction, with the strength of the effect decreasing as the scatter among the points was increased. This decline in strength was almost linear with a logarithmic transform of the dimensions of the stimulus array. We also evaluated the hypothesis that the induction stimulus is detected by one or more channels--for example, neurons--for which the sensitivity profiles are modeled as Gabor wavelets. The change in induction strength with increasing point scatter was not predicted by a single width of channel. However, the combined activity of an ensemble of channels that differed in width did match the perceptual effects if one also stipulated that each channel would respond maximally to a fine-line stimulus.

WOS: 000181323800071 PubMed: 12621222 …

The Poggendorff illusion is a well-documented geometric illusion that involves the brain's perception of the interaction between oblique lines and object contours: an oblique line is apparently mis...

The purpose of this paper is to examine data from two entirely separate academic traditions and to consider whether such combined pool of data offers an opportunity for an expiscation of better understanding of the ancient problem of pictorial perception. The traditions in question are those concerned with the development of pictorial representation through history, they are usually the province of the disciplines of Archeology and History of Art and I shall call them “historical”, and those concerned with the contemporaneous comparisons of perception and execution of pictures in several societies, either by deliberate design or by tacit assumption; these are usually the concern of Psychology and to a lesser extent of Anthropology. Such an examination is also likely to reveal lacunae in these data and therefore show what further work would be profitable.

Subjects made magnitude estimations of fins-in and fins-out Mueller Lyer stimuli. Shaft length, fin length, and fin angle were within-subjects variables, and the sitmuli could be either conventional solid drawings or dot forms, a between-subjects variable. The parametric effects of these variables were similar to results previously obtained. However, principal emphasis was given to lens model and related multivariate analyses of the subjects’ judgments. These analyses suggested that no single “critical” cue seemed to account for the illusion. Rather, various sets of cues could be formulated to simulate the subjects’ judgmental behavior equivalently. In addition, field-independent subjects showed better knowledge of the cue structure than field-dependent subjects. In the main, subjects in this experiment performed like subjects have in tasks not involving visual illusions with multiple sources of information varying in their relevance.

Two experiments are reported which show that (1) a curve tends to be perceived as more curved than its physical dimensions warrant, (2) after a period of inspection there is a decrease in the magnitude of this illusion, and (3) in a minimal cue, monocular viewing, situation a curve is perceived as rotated in space. These findings are used to present a different interpretation of the “Gibson normalization effect”.

Hong Kong Chinese developmental results are presented to test cross-cultural developmental theories relating to changes in illusion susceptibility with age. The Muller-Lyer (M-L) and Sander-Parallelogram (S-P) illusion data confirm the expected decrease with age from 3-12 (Walter, 1942), and the later increase to age 21 due to exposure to a more sophisticated environment (Wapner and Werner, 1957). The data also supported Piaget and Morf's (1956) developmental hypotheses regarding contiguous and noncontiguous versions of the Horizontal-Vertical (H-V) illustions. The United States, Hong Kong, and Arunta cross-cultural comparisons also support the "carpentered world hypothesis," while H-V illusion susceptibility was also related to ecologically valid desert/urban differences in habits of perceptual inference. However, intersample differences in retinal pigmentation and the cross-sectional nature of the study may have influenced the results.

Two experiments were conducted, one utilizing the Titchener circles and the second the Delboeuf target, to determine the effect of size of contextual circle on degree of distortion. The method of adjustment was used in both experiments. The results were very similar to those obtained by indirect psychophysical techniques. The test-retest reliability coefficient for a composite Titchener circles illusion was +.76; for a composite Delboeuf illusion, it was +.77. The correlation between the two types of illusions was +.30. It was also found that in both configurations the illusion of expansion was greater than the illusion of shrinkage, which is consistent with the trend in the Mueller-Lyer illusion.

Three experiments were conducted to examine the effects of multiple fins on the magnitude of the Mueller-Lyer illusion. All studies showed that the multiple form of the elongation illusion was greater than the average of the components and that the multiple form of the shrinkage illusion was smaller than either of the components. The pattern of results failed to support either simple addition models or more complex averaging theories of illusions. A cross-attribute summation hypothesis and a filled space hypothesis were proposed as possible explanations for the results.

The experiment was designed to ascertain whether the distortion of contours by herring-bone backgrounds is determined by the overall form of the background or by the angle at which individual units of the background intersect with the contour. The angle of intersection was reversed either by altering the angle of the background herring-bone units or by varying the angle of the superimposed contour. But these manipulations do not affect the general form of the inducing pattern. In both cases, the direction of the distortion was reversed, supporting the hypothesis that it is the angle of intersection of individual units that is important.

The reading of a point on a graph is influenced by the slope of a line passing from the point in the direction of the calibrated edge against which the point is read. The sloping line is perceived to be too nearly at right angles to the calibrated edge. The direction of the error corresponds to the direction of the slope of the line; the size of the error increases with the distance of the point from the calibrated edge. A number of sloping lines lying between the point and the correct reading on the calibrated edge will increase the size of the illusion. The illusion is of about half the size of the conventional Poggendorff illusion.

Just as circle-size induces differences in the perceived extent of a line which interconnects the circles of the Baldwin illusion, it is demonstrated that circle-size induces differences in the perceived duration of a time interval which intervenes between circles of different sizes.

A new theory of the geometric illusions is presented. Three perceptual processes are described, tending to reduce binocular parallax anomalies for environments containing overlaid objects. Inappropriate operation of these processes gives rise to the illusions. The effects of environmental training on the illusions are considered. Results from cross-cultural studies are cited and used to test a prediction from the theory concerning the magnitudes of cross-cultural differences for two forms of the vertical-horizontal illusion.