Final Exam Study Guide Chapter 10 Perceiving Depth and Size 1 Cue Approach to Depth Perception a Oculomotor Cues feel the positioning of our eyes and tension in eye muscles Created by Convergence when we look at nearby objects Accommodation change in shape of lens occurring when we focus objects at different distances b Monocular Cues work with only one eye i ii i Pictorial Cues sources of depth information that can come from 2 D images 1 Occlusion one object partially covers another a Eg tree occludes a building far away 2 Relative Height a Objects below horizon higher in visual field more b Objects above horizon lower in visual field more distant distant 3 Relative Size when objects equal size closer one takes up more of the visual field a Eg further car smaller than nearer one 4 Perspective Convergence parallel lines appear to come together in distance a Eg train tracks of object sizes 5 Familiar Size distance judged based on previous knowledge a Eg judge position of dime quarter and half dollar 6 Atmospheric Perspective distant objects appear less sharp and have blue tint a Eg looking at Canal ships in distance 7 Texture Gradient separate elements appear more packed as distance increases a Eg buildings in distance on Corredor 8 Shadows indicate where objects are located a Eg balls on checkerboard ii Motion Produced Cues 1 Motion Parallax closer objects glide past faster but objects 2 Deletion and Accretion objects covered or uncovered as we in distance move slower move relative to them a Deletion covering b Accretion uncovering c Binocular Cues depend on both eyes i Binocular Disparity difference in images in both eyes 1 Human eyes spaced 7cm apart so brain gets slightly different pictures of same scene 2 Physiology of Depth Perception a Tsutsui Experiment i Monkeys matched texture gradients that were 2 D pictures and 3 D stereograms Recordings from parietal lobe neuron showed response to ii o Pictorial cues o Binocular disparity Binocular Depth Cells respond best to a specific degree of absolute binocular disparity b Blake and Hirsch Experiment i ii Cats were reared by alternating vision between two eyes Results showed they 1 Had few binocular neurons 2 Were unable to use binocular disparity to perceive depth 3 Perceiving Size a Perception of size depth interaction Our ability to perceive an object s size can sometimes be drastically affected by our ability to perceive the object s distance ii Eg whiteout with helicopter and box on the ground b Visual Angle angle of an object relative to the observer s eye Depends on Size of stimulus Distance of stimulus from observer Objects of different size can have the same visual angle 1 Eg A smaller object thumb can completely cover a larger object that is far away clock As object moves closer to retina the size of the angle increases 1 Halving distance between stimulus and observer doubles the size of the retinal image v Thumb method of determining the visual angle 1 When thumb at arm s length whatever it covers has a visual angle of about 2 degrees i ii c Holway and Boring Experiment distance and size perception interrelated Observer was at the intersection of two hallways A luminous test circle was in the right hallway placed from 10 to 120 feet away A luminous comparison circle was in the left hallway at 10 feet away Task was to adjust the comparison circle to match their perception of the test circle iii iv i i ii iii iv Setup of Holway and Boring s 1941 experiment The observer changes the diameter of the comparison circle in the left corridor to match his or her perception of the size of the test circles in the right corridor Each test circle has a visual angle of 1 degree and is presented separately This diagram is not drawn to scale The actual distance of the far test circle was 100 feet v 4 Phases vi Conclusions 1 Phase 1 the observer has all depth cues so judgments were based on the physical sizes of the circles Removal of depth cues 2 Phase 2 observers performed the task monocularly 3 Phase 3 observers looked through a peephole 4 Phase 4 drapes added in hallway 1 Accuracy levels decreased as depth cues were removed visual angle remained constant 2 Size estimation is based on the actual size of objects when good depth information is available 3 When depth information is not available visual angle is used d Size Constancy perception of object s size remains relatively constant i ii Effect remains even if the size of the object on the retina changes Size distance scaling equation 1 S K R X D S object s perceived size K a constant R the size of the retinal image D the perceived distance of the object iii i ii Changes in distance and retinal size balance each other e Other information Familiar Size use size of familiar objects to judge size of other objects Texture Gradient cylinder example even as textures become closer together we know cylinder the same size because their bases cover the same proportion f Emmert s Law i ii iii Retinal size of an afterimage remains constant Perceived size will change depending on distance of projection This follows the size distance scaling equation 4 Visual Illusions stimulus that is incorrectly interpreted by the visual system a When conditions are such that we receive inaccurate information we experience a non veridical perception b M ller Lyer Illusion i ii Conflicting cues theory Perception of line length depends on 1 The actual length of the vertical lines 2 The overall length of the figure The conflicting cues are integrated into a compromise perception of length c Ponzo Illusion i ii 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 iii d The Ames Room i ii Two equal size people appear very different sizes Room construction a The shape looks like a normal room when viewed with b The actual shape has the left corner twice as far away as one eye the right corner e Moon Illusion i Moon appears larger on horizon than when it is higher in the sky ii One possible explanation 1 Apparent distance theory horizon moon is surrounded by depth cues while moon higher in the sky has none iii Another possible explanation 1 Angular size contrast theory moon appears smaller when surrounded by larger objects 2 Thus the large expanse of the sky makes it appear smaller Chapter 11 Sound The Auditory System Pitch Perception 1 Pressure