Abstract
We report two psychophysical experiments that investigate a visual illusion that is considered common knowledge among type designers, but has never been studied scientifically. Specifically, the thickness of a horizontal line is overestimated in relation to that of a vertical line. Experiment 1 confirmed the existence of the illusion. In Experiment 2, we replicated the effect and showed that the illusion is closely related to the vertical-horizontal illusion, in which the length of a vertical line is overestimated in comparison to a horizontal one. Both the overestimation of thickness and length is larger when the stimulus is surrounded by a horizontally elongated frame, as opposed to a vertically elongated frame. We discuss potential explanations for the thickness illusion and its relation to the vertical-horizontal illusion.
Highlights
Among type designers, it is common knowledge that even the most ordinary letters are subject to a multitude of illusions [1,2,3,4]
Replicating the vertical-horizontal illusion, we found that the mean point of of subjective equality (PSE)
Replicating Experiment 1, we found that the horizontal line was perceived as thicker than the vertical line
Summary
It is common knowledge that even the most ordinary letters are subject to a multitude of illusions [1,2,3,4]. This study investigates one of the most common illusions apparent in type design, which affects the perceived thickness of lines. The perceived thickness of a horizontal line is overestimated in comparison to a vertical line. This particular illusion is demonstrated here in the form of a circle, but type designers compensate for the same illusion in rectilinear shapes, such as an ‘L’ or a ‘T’
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