CHAPTER 10 ability to see distances of objects in environment is your perception of these objects and the scene as a while is based on a two dimensional image on your retina cue approach to depth perception what info is contained in 2 D image that enables us to perceive depth in a scene occlusion a signal or cue that one object is in front of another learned the connection b w this cue and depth through our previous experience with the environment divide cues into 3 groups oculomotor cues based on our ability to sense the position of our eyes and the tension in our eye muscles monocular cues that work with one eye binocular cues that depend on 2 eyes oculomotor cues info derived from the status of eye muscles created by 1 convergence inward movement of the eyes that occurs when we look at nearby objects 2 accommodation the change in the shape of the lens that occurs when we focus on objects at various distances both indicate when an object is close and are useful up to a distance of about arm s length with convergence being the more effective of the 2 idea behind cues is that we can feel the inward movement of the eyes that occurs when the eyes converge to look at nearby objects and we feel the tightening of eye muscles that change the shape of the lens to focus on a nearby object close range monocular cues work with one eye info patterns derived from the environment include accommodation pictorial cues depth information that can be depictured in a 2 D picture movement based cues are based on depth info created by movement pictorial cues sources of depth info that can be depicted in a picture visual cliff apparatus table with clear solid top pattern at 2 levels human infants 6 14 months visual cliff task to crawl to mom cross deep side result new crawlers go experienced crawlers sit stop at cliff until you get experience on your own you don t know pictorial cues they develop occlusion occurs when one object hides or partially hides another form view does not provide info about an objects absolute distance only indicates relative distance ex Hill covers mountains mountains farther away relative height objects that are below horizon and have their bases higher in the field of view are usually seen as being more distant when objects above the horizon being lower in the field of view indicates more distance looking straight out at an object high in visual field near horizon indicates greater depth than looking down as you would for objects lower in visual field ex Picture of cars on road base of car higher on picture is further than base of car closer relative size when two objects are of equal size one that is father away will take up less of your field of view than the one that is closer person s knowledge of physical size ex Telephone poles on a long road in a picture know they re the same size in real life even though they look smaller as they get father away perspective convergence parallel lines extend out from an observer they are perceived as converging becoming closer as distance increases perceptual coming together of parallel lines ex Coming together of train tracks at the further point familiar size when we judge distance based on our prior knowledge of sizes of objects experiment shoes that under certain conditions our knowledge of an object s size influences our perception of that object s distance most effective when other info about depth is absent ex Experiment with the coins pictures of diff coins were all same size but person said they were different sizes bc they were familiar with their real size atmospheric perspective occurs when more distant objects appear less sharp and have a slight blue tint father away object is the more air and particles we have to look through making objects that are farther away look less sharp and bluer than close objects long range ex Scene on the coast of water when high humidity areas further away are blurry unclear static or pictorial monocular depth cues ex Chalk drawing size of monocular depth cue texture gradient elements that are equally spaced in a scene appear to be more closely packed as distance increases ex Picture of cobble stone can tell bricks apart when closer but further away bricks look much closer packed shadows when associated with objects can provide info regarding the locations of these objects enhance the 3 D of objects ex Spheres on checkerboard w and w o shadow w o location unclear w can tell some resting and some floating shading an effect the visual way an object is perceived linear perspective vanishing point provides point of view physically parallel lines converge perceptually with distance pre linear art hieroglyphics attempts at linear perspective in art have shifting vanishing points vanishing points help with one coherent shape motion produced cues motion parallax nearby objects appear to glide rapidly past us but more distant objects appear to move more slowly noting how the image of a near object and a far object move across the retina as the eye moves from position 1 to position 2 the image of the near object travels a large distance across the retina it appears to move rapidly as the observer moves image of far objects travels a much smaller distance across the retina so it appears to move much more slowly one of the most important sources of depth info from animals close and medium range ex When driving in car thing outside side window moving quickly past you things ahead moving slowly deletion as an observer moves sideways and some things become covered accretion as an observer moves sideways and some things become uncovered both are related to motion parallax and overlap bc they occur when overlapping surfaces appear to move relative to one another effective for detecting the differences in the depths of two surfaces binocular depth info binocular disparity difference in the images in the left and right eyes retinal disparity 2 eyes 2 pictures corresponding retinal points the places on each retina that would overlap if one retina could be slid eon top of the other horopter an imaginary surface that passes through the point of fixation and indicates the location of objects that fall on corresponding points on the two retinas point of fixation determining merge jumping thumbs ex right eye closed and then switch shows on right side viewmasters men on moon counterfeit retinal disparity points not on horopter or too close w eyes crossed between you and fixation pt do not have corresponding retinal