Journal of Illusion

The reversed letter-row tilt illusion and an underlying geometrical illusion

Hiroyuki Ito — 2026-09-24

It is known that when a certain set of characters is repeated in a row, the row is perceived to tilt (letter-row tilt illusion). This study reports previously unobserved tilt illusions. We found that when the polarity in luminance contrast of characters in the row is alternated, the direction of the illusory tilt is reversed (reversed letter-row tilt illusion). We extracted horizontal short line segments with a stairs structure that were utilized in typical reversed letter-row tilt illusion figures. We found that the stairs configuration of contrast-alternated short-line segments or dots constitutes a new geometrical illusion (reversed stairs illusion) that is assumed to underlie typical reversed letter-row tilt illusions. Different effects of contrast-polarity reversals were also shown on character rows that produce a letter-row tilt illusion without an explicit stairs structure.

Linton stereo illusion

Paul Linton — 2026-07-01

We present a new illusion that challenges our understanding of stereo vision. The illusion consists of a larger circle at 50 cm, and smaller circle in front of it at 40 cm, with constant angular sizes throughout. We move the larger circle forward by 10 cm (to 40 cm) and then back again (to 50 cm). The question is, what distance should we move the smaller circle forward and backward to maintain a constant perceived separation in depth between the circles? Constant physical distance (10 cm) or constant retinal disparity (6.7 cm)? Observers choose constant retinal disparity. The ‘Linton Stereo Illusion’ therefore appears to suggest that perceived stereo depth reflects retinal disparities rather than 3D geometry.

Learning a surfaces’ shape from binocular disparity and perceiving it from shading

Tadamasa Sawada — 2026-06-26

Some special images are known to produce a learning effect in 3D perception. This image represents a 3D scene but it has been degraded so that the 3D information of the scene can be perceived from the image only after the learning has taken place. This study presents a new type of image that is not degraded but can produce a learning effect in 3D perception. This image has a luminance gradient of shading that represents a saddle (hyperbolic) shape that is perceived on the basis of the gradient only after the saddle shape has been learnt on the basis of binocular disparity. This learning effect suggests that the 3D information can be transferred across depth cues in the visual system.

Fast positive motion aftereffect arising in the afterimage of rotating ‘Enigma’

Hiroyuki Ito — 2026-09-25

Enigma is an Op art piece that induces an illusory flow in rings on a radial sunburst pattern. We report that, after an Enigma pattern was slowly rotated and then removed, a fast rotation of the rings’ afterimage in the same direction as the previous rotation was perceived. The phenomenon is demonstrated with movies and experimental results.