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Introduction to the Experiment

This experiment will use the method of adjustment to determine how much the Müller-Lyer illusion may distort your perception of relative line lengths. The applet will present an image of two lines of different lengths, one above the other (see figure1 below). The upper line is a standard stimulus line, and will be the same length throughout this experiment. The lower line is a comparison stimulus line, which you will be able to make longer or shorter than the standard. Each line will have arrowheads on its ends: the standard line will have arrowheads pointing inward; the comparison line will have arrowheads pointing outward on some trials and inward on other trials. By adjusting the length of the comparison line so that it appears to match the length of the standard line, this experiment will measure the effect of the Müller-Lyer illusion on your perception of relative length (i.e., your judgment about the relative lengths of the comparison and standard lines):


figure 1