Hockenbury Discovering Psychology 5th txtbk

Perception119Depth PerceptionHow Far Away Is It?Key Theme• Perception of distance and motion helps us gauge the position ofstationary objects and predict the path of moving objects.Key Questions• What are the monocular and binocular cues for distance or depth perception,and how does binocular disparity explain our ability to see threedimensionalforms in two-dimensional images?• What visual cues help us perceive distance and motion?• Why do we perceive the size and shape of objects as unchanging despitechanges in sensory input?Being able to perceive the distance of an object has obvious survival value, especiallyregarding potential threats, such as snarling dogs or oncoming trains. But simplywalking through your house or apartment also requires that you accurately judgethe distance of furniture, walls, other people, and so forth. Otherwise, you’d beconstantly bumping into doors, walls, and tables. The ability to perceive the distanceof an object as well as the three-dimensional characteristics of an object iscalled depth perception.Monocular CuesWe use a variety of cues to judge the distance of objects. Monocular cues requirethe use of only one eye (mono means “one”). When monocular cues are used byartists to create the perception of distance or depth in paintings or drawings, theyare called pictorial cues. After familiarizing yourself with these cues, look at thephotographs on the next page. Try to identify the monocular cues you used todetermine the distance of the objects in each photograph.1. Relative size. If two or more objects are assumed to be similar in size, the objectthat appears larger is perceived as being closer.2. Overlap. When one object partially blocks or obscures the view of another object,the partially blocked object is perceived as being farther away. This cue isalso called interposition.3. Aerial perspective. Faraway objects often appear hazy or slightly blurred by theatmosphere.4. Texture gradient. As a surface with a distinct texture extends into the distance, thedetails of the surface texture gradually become less clearly defined. The texture ofthe surface seems to undergo a gradient, or continuous pattern of change, fromcrisp and distinct when close to fuzzy and blended when farther away.5. Linear perspective. Parallel lines seem to meet in the distance. Forexample, if you stand in the middle of a railroad track and look downthe rails, you’ll notice that the parallel rails seem to meet in thedistance. The closer together the lines appear to be, the greater theperception of distance.6. Motion parallax. When you are moving, you use the speed of passing objectsto estimate the distance of the objects. Nearby objects seem to zipby faster than do distant objects. When you are riding on a commutertrain, for example, houses and parked cars along the tracks seem to whizby, while the distant downtown skyline seems to move very slowly.Another monocular cue is accommodation. Unlike pictorial cues, accommodationutilizes information about changes in the shape of the lens of thedepth perceptionThe use of visual cues to perceive the distanceor three-dimensional characteristics ofobjects.monocular cues(moe-NOCK-you-ler) Distance or depth cuesthat can be processed by either eye alone.Depth Perception in Photographs Severalmonocular cues combine to produce theillusion of depth in this photgraph of theGinza, a major shopping and entertainmentdistrict in Tokyo. See if you canidentify examples of relative size, overlap,aerial perspective, texture gradient, andlinear perspective.