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Test 1

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  1. Test 1 • Covers material through fixation disparity • 20 multiple choice questions • Study guide questions and problem set • Do not need to know formula for calculating the amount of fixation disparity.

  2. Cues to Depth

  3. What happens when you close one eye? • Still appreciate depth • Monocular cues help us with depth perception. • Patient’s often confused about this.

  4. Characteristics • Cues not hard wired • Learned inferences that the visual system makes.

  5. Monocular Cues to Depth in a deprived environment • Retinal image size-this cue works when other cues are absent • Emmert’s law – the perceived size of the object producing a retinal image of given fixed size is proportional to its perceived distance.

  6. Emmert’s Law • Example • Afterimage

  7. Problem with using retinal images • We do not perceive real life objects based on visual angle. • Familiar objects would be growing or shrinking • Need an invariant or constant to compensate for retinal image size

  8. Holway/Boring Experiment

  9. Size Constancy • Perception needs to account for both distance and retinal size • S=K(RxD) • S is perceived size • K is a constant • R is retinal image size • D is perceived distance

  10. Monocular Cues in Natural Setting • See website this is different than in lecture notes. • http://sites.sinauer.com/wolfe3e/chap6/startF.htm

  11. Stereopsis • This is true depth perception. • Preattentive

  12. Absolute Depth • Distance from egocentric position • More dependant on monocular cues

  13. Relative Depth • Objects in relation to each other • Stereopsis ideal for detecting this

  14. Types of Disparity • Horizontal vs. vertical disparity • Other types of disparity • Disparity gradients give rise to tilted surfaces • Orientation disparity

  15. Types of Disparity • Horizontal vs. vertical disparity • Other types of disparity • Disparity gradients give rise to tilted surfaces • Orientation disparity

  16. Special Cases • Chromostereopsis • Result of chromatic aberration • Longitudinal vs transverse

  17. Stereoacuity • Depth discrimination threshold • Hyperacuity similar to vernier acuity – can get 4 to 5 seconds of arc

  18. Howard-Dolman • Calculating disparity – Howard Dolman Apparatus • n = 2a/2.9 x 10-4 x d/d2 • n = angular stereoscopic disparity in radians • 2a = interpupillary distance • d = fixation distance • change in d = linear distance between the two rods

  19. Characteristics • Effect of exposure time • Retinal eccentricity • Background illumination

  20. Measuring Stereoacuity • Howard Dolman apparatus • Method of adjustment • Method of limits

  21. Stereopsis upper limit • Patent or quantitative stereopsis • Latent or qualitative stereopsis

  22. Purpose of coarse stereo • Processing of depth outside the horopter • Cue for the vergence system • Back up stereo system • May be primary stereo signal for small angle strabismus.

  23. Stereo Targets • Local stereopsis • Line targets • Provides monocular cues • Best used for Stereoacuity measures

  24. Global Stereopsis • Random dot stereogram – provides no monocular cues to depth • May play a role in detecting camouflaged object • Targets have to be fused for form perception to occur

  25. Characteristics • Stereo correspondence problem or how does the visual system decide which dots to fuse. • The visual system yields the best global interpretation of depth • Depth averaging