The reader is probably familiar with optical illusions, where one doesn't think one sees what in fact one is seeing. For example, the reader may be asked to judge which of two lines is longer. From the way that the two lines are presented, one line does indeed look longer than the other. However, on measuring the lines with a ruler, they are found to be identical in length. This is an optical illusion -- your eyes and brain have tricked you into seeing something that isn't really so.
Word Ways: Vol. 5
, Article 4.
Available at: https://digitalcommons.butler.edu/wordways/vol5/iss1/4