September 2021
Volume 21, Issue 9
Open Access
Vision Sciences Society Annual Meeting Abstract  |   September 2021
Does the vertical-horizontal illusion explain over-estimation of perceived step height?
Author Affiliations
  • Andrew Schofield
    Aston Unversity
Journal of Vision September 2021, Vol.21, 2028. doi:
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      Andrew Schofield; Does the vertical-horizontal illusion explain over-estimation of perceived step height?. Journal of Vision 2021;21(9):2028.

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      © ARVO (1962-2015); The Authors (2016-present)

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In the vertical-horizontal illusion (VHI) observers overestimate the length of a vertical line relative to a horizontal especially when presented in a ‘T’ configuration. This illusion his has been used to accentuate the perceived height of steps with a vertical grating on the riser and a step-edge highlighter forming the horizontal bar. Patterned steps with the edge highlighter are typically compared to blank steps. Consequently, other effects may contribute to misperceived height including aggregation of the thick highlighter into the step height, and the filling of the patterned step with modulations (filled intervals appear larger). Various configurations of the VHI were tested including vertical luminance gratings (L) and second-order modulations of contrast, CM; orientation, OM; and spatial frequency, FM. Over 3 experiments, observers were asked to compare the apparent height of gratings with that of either filled, unmodulated rectangles or unfilled rectangles. Rectangles were presented alone or as part of a step with a highlighter. Highlighters sometimes matched the properties of the grating, sometimes not, and where sometimes separated from the gratings by a thin line. Observers undertook 2ifc judgements indicting which of a test or standard rectangle appeared taller. All gratings except FM appeared taller when presented in the step configuration with a contiguous highlighter matching the properties of the grating. However, this effect was greatly reduced when a thin line separated the grating from the highlighter and abolished when the highlighter did not match the grating. In the rectangle conditions, all cues except FM appeared taller than blank rectangles and L and CM appeared taller than filled-unmodulated rectangles. In conclusion, the ability of vertical stripes and edge-highlighters to accentuate step height may be due to aggregation of the highlighter into the grating and filled interval effects. Further, second-order CM and OM modulations produce a similar illusion.


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