Abstract: An experiment on perpendicular illusion was made with 20 college studentsand young workers by using a set of tilted parallel lines as the inducing partof the stimulus. The effect of perpendicular illusion was found in the almostvertically and horizontal1y located testing lines, and the magnitude of perpen-dicular illusion was closely related to the tilt angle of the inducing lines,but when the two parts of the stimulus were seperated apart for each eye,and then looking through a stereoscope, the perpendicular illusion was no moreobserved: This suggested that the perpendicular illusion is li?nly to be initiatedon the retina, and it may be explained by the theory of lateral inhibition.

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