Perceptual similarity of mirror images in infancy

Abstract

Perception of mirror images by three-to four-month infants was studied in five experiments using habituation paradigms. In the first experiment, babies discriminated right profiles of two different faces but not the left and right profile of the same face. In the second, babies discriminated a 45° oblique from a vertical line, but not the oblique from its mirror image. In the third, babies discriminated oblique lines that differed by 50° and were not mirror images. In the final experiments. 90° rotations of a ⊏-shape were discriminated but not 180° rotations that formed lateral or vertical mirror images. These results demonstrated that although babies were able to discriminate differences in orientation (even among obliques) they tended to view mirror images, especially lateral mirror images, as equivalent stimuli. We propose that the perceptual equivalence of mirror images reflects an adaptive mode of visual processing; mirror images in nature are almost always aspects of the same object, and they usually need not be discriminated. The relations of the perceptual similarity of mirror images to the ontogeny of the object concept and to the development of reading are discussed.