Depth Perception
In Chap. 7 , the reader is invited to understand that the capacity to see the world in three dimensions, that is, of perceiving depth, is based on the availability and contribution of several cues. The main cues for perceiving depth could be based on bin
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Depth Perception
The possibility to see the world in three dimensions remains quite fascinating considering the following peculiar fact: images arrive on the retina in two dimensions. Spontaneously, no one would doubt that there is a physical world that includes a third dimension. Nevertheless, the brain has to build this third dimension. The present chapter addresses this phenomenon, that of the construction of space or, more specifically, of depth. In the preceding chapters, different aspects of visual perception sent the reader back to fundamental concepts of physics for understanding the nature of stimuli or to fundamental concepts of physiology or brain sciences for understanding biological bases of perception. In the present chapter, special attention is paid to psychological phenomena allowing to perceiving this third dimension. After a review of the main cues for perceiving depth, two phenomena are examined closely. The first one, perceptual constancy, is fundamental and is indeed not involved only in depth perception. The second one reveals cases, most often fascinating and fun, where these cues are misleading and induce illusions.
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Cues for Perceiving a Third Dimension
The capacity of perceiving depth is based on the availability and contribution of several cues. These cues are kind of tricks allowing the brain to generate this impression of depth. However, using these tricks requires no voluntary effort; they are spontaneously activated by the data provided by the visual scene. For understanding how these cues are studied in the field of perception, it is appropriate to make some distinctions between terms or concepts. First, for studying
© Springer International Publishing Switzerland 2016 S. Grondin, Psychology of Perception, DOI 10.1007/978-3-319-31791-5_7
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Depth Perception
the estimated distance, for example, researchers will distinguish absolute distance and relative distance. The idea of absolute distance, sometimes also called selfcentered, refers to the estimation of the distance between an object and the one observing this object. In contrast, reference is made to relative distance, or exocentric distance, to designate the distance between the objects or between parts of these objects. If we generally find it hard to precisely estimate the absolute distance, we are rather good to decide if an object is closer to us than another object. In addition to this absolute vs. relative distance distinction, it is important to keep in mind that the various depth cues that can be used can be classified in the following three dichotomous categories. Cues may be extraocular (nonvisual) rather than visual. Thus, information on depth might not be extracted specifically from the visual system per se, but from a source belonging to another sensory modality, namely, the kinesthetic system. Another useful distinction is the one between pictorial cues, which are static, and kinematic cues, which are dynamic, i.e., related to movement. Finally, there are binocular cues, as opposed to monocular
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