> The horizontal-vertical illusion is a phenomenon in which the vertical line appears longer when a horizontal line and a vertical line of the same length are d

> The horizontal-vertical illusion is a phenomenon in which the vertical line appears longer when a horizontal line and a vertical line of the same length are drawn. For example, it has been shown that when a building that is in fact 10 meters both along its frontage and in height is viewed, it seems to the viewer that the height is 1.4 times the width, making the building look 14 meters tall. The first sentence is manifestly false. If you take the example image in the article and rotate it 90 degrees, so that the red line is horizontal and the black line is vertical, then it's still the red line that looks longer (admittedly I find the effect is a bit weaker). What's really going on is that the impact of black line's length is reduced by having something halfway along it, while the red line is unbroken. Either the image represents a different illusion or (and I guess this is really it) it's not that vertical lines necessarily look longer, it's just that, in practice, they're more likely to be unbroken (like the red line) while horizontal lines are more likely to have other things visually impacting their apparent length.