Stereovision. Binocular disparity

Transcription

1 Stereovision Binocular disparity

2 Retinal correspondence Uncrossed disparity Horoptor Crossed disparity Horoptor, crossed and uncrossed disparity Wheatsteone stereoscope (c. 1838)

3 Red-green anaglyph How to make a random-dot stereogram Left eye image Right eye image x A A y B B

4 Disparity selectivity in V1 Distribution of disparity preferences

5 Disparity-selective simple cells left right Monocular monocular A linear linear left B C binocular Binocular linear linear monocular energy right A Zero zero disparity disparity B Position position shift shift C Phase phase shift shift D A binocular energy monocular linear reference point left right binocular Disparity-selective complex cells B linear monocular Monocular energy C energy Binocular binocular D energy energy Selective for 0 disparity Disparity-selective complex cells zero A Zero left right disparity disparity position B Position shift shift phase C Phase shift shift

6 Disparity-selective complex cells the mismatched contrast pair has a different one sees the same value than that for the matched pair. These described above. Co findings show that the complex cell rejects properties of the c A L R L R L R L R < X Nw Simple a d 1\ 'a t - ] cell 0 ~ ~~~ 4-, '' D i 0 = Complex r t 4 3 cell Things that can happen with 2 eyes Fusion Suppression Diplopia Rivalry Binocular rivalry

7 Working hypothesis: neural activity in primary visual cortex is conscious visual awareness optic nerve Right eye V1 LGN primary visual cortex (V1) Left eye Prediction: traveling waves of cortical activity Brain Percept Perceptual and neural traveling waves Peak fmri response Percept

8 Activity correlates with perceived latency # of trials Behavior 1 3 Latency (s) Infer ~115 ms timing difference over ~3.5 mm distance. fmri response latency (sec) Behavioral latency sec sec 2-3 sec Distance (cm) Estimated neural latency Neural latency Time Estimated neural latency (sec) Ave speed = 2 cm/sec Distance (cm) Observer DN PN SL Diverted attention left eye right eye Cdisplay C C2DA3B42D... Time Detect repetition

9 Diverting attention preserves waves in V1 but eliminates them in V2 & V3 Waves measured with VDSI in monkey V1 Waves measured with VDSI in monkey V1

10 Implications: neural processing hierarchy Rest of brain Right eye V1 Attention Left eye Feedback Binocular rivalry models A Summation (LR) Opponency Unit (R-L) Left Monocular Right Monocular B C D Response L. Eye R. Eye Time (s) Winner take all index Distance, depth, and 3D shape cues Pictorial depth cues: familiar size, relative size, brightness, occlusion, shading and shadows, aerial/ atmospheric perspective, linear perspective, height within image, texture gradient, contour. Other static, monocular cues: accommodation, blur. Motion cues: motion parallax, kinetic depth effect, dynamic occlusion. Binocular cues: convergence, stereopsis/binocular disparity.

11 Monocular depth cues Retinal projection depends on size and distance Ames room Ames room

12 Familiar size (Epstein 1965) How far away is the coin? Occusion as a cue to depth Texture 1. density 2. size 3. foreshortening

13 Shading, reflection, and illumination illumination occlusion reflectance shading Shading Shading (flip the photo upside down)

14 Cast shadows Dynamic cast shadows Shading and contour

15 Linear perspective Aerial/atmospheric persepective Size constancy

16 Size contrast Motion parallax The kinetic depth effect