August 2016
Volume 16, Issue 12
Open Access
Vision Sciences Society Annual Meeting Abstract  |   September 2016
Holistic and analytic observation of the vertical-horizontal illusion: the way of looking at things alters percept of line length
Author Affiliations
  • Masahiro Ishii
    Sapporo City University
Journal of Vision September 2016, Vol.16, 294. doi:10.1167/16.12.294
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      Masahiro Ishii; Holistic and analytic observation of the vertical-horizontal illusion: the way of looking at things alters percept of line length. Journal of Vision 2016;16(12):294. doi: 10.1167/16.12.294.

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      © 2017 Association for Research in Vision and Ophthalmology.

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Abstract

A figure that consists of two lines forming an inverted T shape creates a geometrical illusion. The vertical line appears to be longer than a horizontal line of equal length (the vertical-horizontal illusion). People mostly judge the line length from the holistic appearance of the figure, concerning its proportions. There is more than one way to judge the length of the vertical line relative to the length of the horizontal line. An analytic observation is a possibility. One, for instance, can mentally rotate and translate the horizontal line to compare with the vertical line side-by-side in the plane of representation. In the present study, we examine whether an analytic observation modulates the line length judgment of the VH illusion. An experiment, using the method of adjustment technique, was conducted to measure the point of subjective equality, where the vertical line seemed to be the same length as the horizontal line. 168 observers participated. Each participant performed two trials in a row: one trial by a holistic observation and the other by an analytic observation. The viewing distance was 50 cm and the horizontal line subtented 5.7 degree constantly. For the holistic observation, they overestimated the length of the vertical line an average of 16.8%. For the analytic observation, by contrast, they overestimated the length an average of 4.9%. The illusion was significantly smaller with the analytic observation than with the holistic observation. One theoretical accounts of the VH illusion is the perspective theory, a vertical line is perceived as receding from the observer, whereas a horizontal line is perceived to lie in the display surface. It may be assumed that the 2D mental rotation counteracts the illusory 3D recession of the vertical line.

Meeting abstract presented at VSS 2016

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