engleski

The illusion of the snow tire traffic sign

The traffic sign B45 shows a chained automobile tire that is oriented towards the observer and which is placed inside the blue circle. It has been noticed that the outer blue circle appears distorted in horizontal manner. The aim of this study was to demonstrate and to measure the size of this illusion. Two experiments were conducted ; one using the method of adjustment, and the other the method of constant stimuli. Both experiments consisted of three situations – blue circle (control), blue circle with the white ellipse inside, and the B45 sign. The point of subjective equality was measured. Participants’ task was to set the width of the object that varied randomly so that it forms a perfect circle. The ANOVA analysis showed significant effect, but only the “ellipse” situation differed significantly from the control situation. In the second experiment the participants had to decide whether the presented stimuli were distorted in horizontal or vertical manner. The ANOVA analysis on the points of subjective equality showed significant effect where both – “ellipse” and B45 situations significantly differed from the control situation. This indicates that there is a moderate but significant tendency to perceive such circles as horizontally distorted.

traffic sign illusion; snow tire sign illusion; distortion of circle; circle perception

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