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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.

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...

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”.

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.