The Muller-Lyer figure and the fly

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Science  31 Oct 1975:
Vol. 190, Issue 4213, pp. 479-480
DOI: 10.1126/science.1166319


In the Muller-Lyer illusion two horizontal line segments of equal length are perceived by humans as unequal. The gaze of a fly presented with Muller-Lyer figures corresponds to human eye movements and human (illusionary) evaluations of the segment lengths. It is suggested that a theory similar to the phenomenological theory which accounts for the fly's gaze may account for the human eye's movement during an observation of Muller-Lyer figures.