One of us has frequently chosen a pot lid that was too big. Hypothesizing the error was a problem with foreshortening, we depicted a cylinder in parallel perspective, tilted 30°, with the top circle foreshortened to a 2D ellipse. Parallel projection provides foreshortening without convergence. Observers judged which of two 2D ellipses was identical to the one depicting the cylinder’s top. One had the same dimensions as the ellipse depicting the cylinder top, 40 mm wide and 15 mm tall, and the other one was bigger, 41 x 18. The observers chose the bigger ellipse. An ellipse depicting a cylinder’s top may look bigger because of crosstalk from perceptual information for a circle in perspective. This information for a tilted 3D surface “biases” perception -- merely biasing the 2D ellipse towards the circle. The 2D ellipse’s apparent eccentricity is simply lessened -- it does not go all the way to a perfect circle. With respect to our original errors with real pot lids, if depicting ellipses can be biased towards circles then surely really circular pot lids can be similarly biased towards ellipses, when the lids are viewed highly tilted.

Mastandrea, S., Hammad, S., Kennedy, J.m. (2012). The Pot/Lid illusion in parallel perspective, 41, 90-90.

### The Pot/Lid illusion in parallel perspective

#### Abstract

One of us has frequently chosen a pot lid that was too big. Hypothesizing the error was a problem with foreshortening, we depicted a cylinder in parallel perspective, tilted 30°, with the top circle foreshortened to a 2D ellipse. Parallel projection provides foreshortening without convergence. Observers judged which of two 2D ellipses was identical to the one depicting the cylinder’s top. One had the same dimensions as the ellipse depicting the cylinder top, 40 mm wide and 15 mm tall, and the other one was bigger, 41 x 18. The observers chose the bigger ellipse. An ellipse depicting a cylinder’s top may look bigger because of crosstalk from perceptual information for a circle in perspective. This information for a tilted 3D surface “biases” perception -- merely biasing the 2D ellipse towards the circle. The 2D ellipse’s apparent eccentricity is simply lessened -- it does not go all the way to a perfect circle. With respect to our original errors with real pot lids, if depicting ellipses can be biased towards circles then surely really circular pot lids can be similarly biased towards ellipses, when the lids are viewed highly tilted.
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2012
Mastandrea, S., Hammad, S., Kennedy, J.m. (2012). The Pot/Lid illusion in parallel perspective, 41, 90-90.
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Utilizza questo identificativo per citare o creare un link a questo documento: `https://hdl.handle.net/11590/175665`
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