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The Müller-Lyer Illusion (MLI) has been suggested as a potential marker for the perceptual impairments observed in schizophrenia patients. Along with some positive symptoms, these deficits are not easily modeled in rodent experiments, and novel animal models are warranted. Previously, MK-801 was shown to reduce susceptibility to MLI in monkeys, raising the prospects of an effective perception-based model. Here, we evaluate the translational feasibility of the MLI task under NMDA receptor blockage as a primate model for schizophrenia. In Experiment 1, eight capuchin monkeys (Sapajus spp.) were trained on a touchscreen MLI task. Upon reaching the learning criteria, the monkeys were given ketamine (0.3 mg/kg; i.m.) or saline on four consecutive days and then retested on the MLI task. In Experiment 2, eight chronic schizophrenia patients (and eight matching controls) were tested on the Brentano version of the MLI. Under saline treatment, monkeys were susceptible to MLI, similarly to healthy human participants. Repeated ketamine administrations, however, failed to improve their performance as previous results with MK-801 had shown. Schizophrenic patients, on the other hand, showed a higher susceptibility to MLI when compared to healthy controls. In light of the present and previous studies, the MLI task shows consistent results across monkeys and humans. In spite of potentially being an interesting translational model of schizophrenia, the MLI task warrants further refinement in non-human primates and a broader sample of schizophrenia subtypes.

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.

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 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.