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

Hiroyuki Ito; Xiaoqian Peng; Yukyu Araragi

doi:10.47691/joi.v6.13927

Hiroyuki Ito Faculty of Design, Kyushu University, Shiobaru, Minami-ku, Fukuoka-shi, Japan https://orcid.org/0000-0003-0344-5374
Xiaoqian Peng Graduate School of Design, Kyushu University, Shiobaru, Minami-ku, Fukuoka-shi, Japan
Yukyu Araragi Faculty of Human Sciences, Shimane University, Matsue, Shimane, Japan

DOI: https://doi.org/10.47691/joi.v6.13927

Keywords: letter-row tilt illusion, reversed letter-row tilt illusion, contrast polarity, geometrical illusion, reversed stairs illusion

Abstract

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.

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