alt Hacker NewsAs someone who wears corrective lenses for astigmatism, I can guarantee that what you perceive as a straight line, assuming you are human, is not, until your brain corrects it and signals 'straight line' to you.
That is unrelated to astigmatism. In Art 101 class in college we explored this phenomenon. It's caused by the spherical nature of the human eyeball.
The exercise was to sit on the floor in the corner of a particular campus building that had a lot of long architectural lines and draw what you see without looking at the paper. If you drew straight lines, the prof knew you were thinking about drawing, and not just drawing what you saw.
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Not so sure. When I first started wearing glasses for astigmatism, it turned rectangles into trapezoids. Totally destroyed my depth perception. After a while I got used to it and stopped walking into curbs and buildings. Later in life I moved to progressive lenses. The straight lines then became curves. Adjusted after a while again, but the curves never fully went away. Regardless, I have to take the glasses off for sports that require good depth perception like ping pong or tennis.
Yeah. If you try hard enough, you can slightly break the correction and directly notice the curvature of the straight lines, especially long ones moving towards you, on the border of your visual field. The eye physically produces a heavily distorted picture, but it's at least partially rectified and the brain does a sort of continuous neural SLAM, what you perceive is the result of it.