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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. Cues to Depth. What happens when you close one eye?. Still appreciate depth

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## Test 1

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**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.**What happens when you close one eye?**• Still appreciate depth • Monocular cues help us with depth perception. • Patient’s often confused about this.**Characteristics**• Cues not hard wired • Learned inferences that the visual system makes.**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.**Emmert’s Law**• Example • Afterimage**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**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**Monocular Cues in Natural Setting**• See website this is different than in lecture notes. • http://sites.sinauer.com/wolfe3e/chap6/startF.htm**Stereopsis**• This is true depth perception. • Preattentive**Absolute Depth**• Distance from egocentric position • More dependant on monocular cues**Relative Depth**• Objects in relation to each other • Stereopsis ideal for detecting this**Types of Disparity**• Horizontal vs. vertical disparity • Other types of disparity • Disparity gradients give rise to tilted surfaces • Orientation disparity**Types of Disparity**• Horizontal vs. vertical disparity • Other types of disparity • Disparity gradients give rise to tilted surfaces • Orientation disparity**Special Cases**• Chromostereopsis • Result of chromatic aberration • Longitudinal vs transverse**Stereoacuity**• Depth discrimination threshold • Hyperacuity similar to vernier acuity – can get 4 to 5 seconds of arc**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**Characteristics**• Effect of exposure time • Retinal eccentricity • Background illumination**Measuring Stereoacuity**• Howard Dolman apparatus • Method of adjustment • Method of limits**Stereopsis upper limit**• Patent or quantitative stereopsis • Latent or qualitative stereopsis**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.**Stereo Targets**• Local stereopsis • Line targets • Provides monocular cues • Best used for Stereoacuity measures**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**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

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