Experiment by Holway and Boring ? continued ? Part 1 of the experiment provided observers with depth cues. ? Judgments of size were based on physical size. ? Part 2 of the experiment provided no depth information. ? Judgments of size were based on size of the retinal images. Size Constancy ? Perception of an object?s size remains relatively constant. ? This effect remains even if the size of the retinal image changes. ? Size-distance scaling equation ? S = K (R X D) not on test ? The changes in distance and retinal size balance each other Size-Distance Scaling ? Emmert?s law: ? Retinal size of an afterimage remains constant. ? Perceived size will change depending on distance of projection. ? This follows the size-distance scaling equation. Visual Illusions ? Nonveridical perception occurs during visual illusions. ? Müller-Lyer illusion: ? Straight lines with inward fins appear shorter than straight lines with outward fins. ? Lines are actually the same length. Müller-Lyer Illusion ? Why does this illusion occur? ? Misapplied size-constancy scaling: ? Size constancy scaling that works in 3-D is misapplied for 2-D objects. ? Observers unconsciously perceive the fins as belonging to outside and inside corners. ? Outside corners would be closer and inside corners would be further away. ? Since the retinal images are the same, the lines must be different sizes. ? Problems with this explanation: ? The ?dumbbell? version shows the same perception even though there are no ?corners.? ? The illusion also occurs for some 3-D displays. Ponzo Illusion ? Horizontal rectangular objects are placed over railroad tracks in a picture. ? The far rectangle appears larger than the closer rectangle but both are the same size. ? One possible explanation is misapplied size-constancy scaling. The Ames Room ? Two people of equal size appear very different in size in this room. ? The room is constructed so that: ? The shape looks like a normal room when viewed with one eye. ? The actual shape has the left corner twice as far away as the right corner. ? One possible explanation - size-distance scaling ? Observer thinks the room is normal. ? Women would be at same distance. ? Woman on the left has smaller visual angle (R). ? Due to the perceived distance (D) being the same her perceived size (S) is smaller ? This is using the size-distance scaling equation (S = R X D). Anjali
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