2002/02/12PSYC202, Term 2, Copyright Jason Harrison Recovery of World Structure: Art and Image

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Task of visual perception Stay alive, reproduce, make art Estimate properties of world using light falling on retina Information: –originates from light reflected from objects –internal knowledge (evolutionary/experience) Combined to recover “true” object properties

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Complications, complications… 1.Illumination (intensity, hue, motion) 2.Projection (3D world to 2D images) 3.Fragmentation (occlusion)

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Illumination intensity, hue, motion varies from spot to spot, moment to moment recover “true” surface properties From What material is this?

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection (3D world to 2D images) recover depth and spatial organization depth enables two abilities: a.shape constancy true 3D shape of object b.size constancy true 3D size of object

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Fragmentation (occlusion) objects not always connected in image From

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Complications, complications… 1.Illumination (intensity, hue, motion) 2.Projection (3D world to 2D images) 3.Fragmentation (occlusion)

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection a. shape constancy Perceived shape of object does not change as orientation changes Shape of image on retina changes From

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection a. shape constancy Same image could be due to: - different shapes - different orientations - different depths

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection a. shape constancy if shape known –depth and orientation can be “guessed”

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection a. shape constancy if depth known –shape and orientation can be “guessed”

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection b. size constancy known object size retinal size determines depth depth cues determine size From

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection b. size constancy known object size retinal size determines depth depth cues determine size

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection b. size constancy known object size retinal size determines depth depth cues determine size

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection b. size constancy

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection b. size constancy

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection b. size constancy

2002/02/12PSYC202, Term 2, Copyright Jason Harrison angle  depends only on ratio s/d Projection b. size constancy

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection b. size constancy

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection b. size constancy Angle  the same as long as s/d the same larger or smaller objects can have same  -  1 = s2 d1 d2

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Projection b. size constancy  is known (from retinal size) -> tan       if size is known, distance follows if distance is known, size follows

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Size and Shape Constancy depend on experience depend on expectations “top down” processes how else can we recover depth from images? what depth cues are available?

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Depth cues 1.Pictorial cues (single image) –art techniques (perspective, shading, occlusion) 2.Multi-point cues (multiple images) –motion cues (kinetic depth, motion parallax) –binocular cues 3.Physiological cues (real stimuli) –accommodation of lens –vergence movements

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Pictorial cues occlusion/interposition shading shadows perspective texture gradient height in plan aerial perspective familiar size

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Occlusion/Interposition nearer object occludes further one

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Occlusion/Interposition nearer object occludes further one critical feature “T-junction”

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Shading lightness constancy: shading determines shape uniform reflectance: 3D shape from shading lighting from above –bumps are light on top –dents are light on bottom

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Countershading confuse interpretation of shape

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Countershading on the BB-55 USS North Carolina ( ) more difficult to see or determine barrel diameter From

2002/02/12PSYC202, Term 2, Copyright Jason Harrison with shadows perceived as standing (3D) Shadows dark patches interpreted as shadows lighting from above Ball and shadow demo

2002/02/12PSYC202, Term 2, Copyright Jason Harrison without shadows perceived as flat (2D) (applications to computer interfaces) Shadows dark patches interpreted as shadows lighting from above Ball and shadow demo

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Perspective parallel lines in world converge to a vanishing point in image lines that converge are parallel in world

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Texture gradient perspective: location of texture items and changes in size/shape of texture items

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Change in texture gradient: change in shape and depth From

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Height in plane (distance from horizon) objects closer to horizon appear further away Same object, one closer to horizon: smaller or further away?

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Aerial perspective (da Vinci) smog, haze, etc. scatter light –objects father away: more scattering –if object surrounded by haze, appears farther away

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Without haze, objects appear equally distant Aerial perspective (da Vinci) smog, haze, etc. scatter light –objects father away: more scattering –if object surrounded by haze, appears farther away

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Aerial perspective Why do mountains look closer on a clear day? “Whoa, look at the mountains!” Visual system assumes average amount of haze –more haze, more distance object must be –less haze, less distant object must be –on a clear day, less haze than usual mountains appear closer than normal

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Familiar size if size of object is known –perceived size = true size –depth is inferred

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Pictorial cues occlusion/interposition shading shadows perspective texture gradient height in plan aerial perspective familiar size

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Multi-point cues kinetic depth (motion of object) motion parallax (motion of observer) binocular stereopsis (see lecture from January 29 for kinetic depth and motion parallax)

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Binocular Stereopsis recovery of 3D depth via 3D displacement of eyes each eye sees slightly different image

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Left eyeRight eye Binocular Stereopsis recovery of 3D depth via 3D displacement of eyes each eye sees slightly different image

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Binocular Stereopsis amount of difference between image depends on depth –depth can be calculated exactly from differences –as if angles between eyes were used limitation: depth less than 3 meters limitation: requires matching images (escalator)

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Binocular Stereopsis: stereoscope use two static images one for each eye –coloured glasses, polarized lenses, lenses –divergence of eyes: practice, practice, practice

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Binocular Stereopsis there are always two slightly different images entering visual system double vision rarely occurs to avoid double vision (binocular rivalry) –suppress input from one eye –dominant eye is “attended” –non-dominant eye is “unattended” –if two completely different images are presented attention (and cortex activity) switches back and forth

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Binocular rivalry Tong et al 1998 two different images –face and house presented either –simultaneously –sequentially same fMRI responses rivalry resolved below high-level areas From

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Multi-point cues kinetic depth (motion of object) motion parallax (motion of observer) binocular stereopsis (see lecture from January 29 for kinetic depth and motion parallax)

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Physiological cues - real stimuli accommodation –focusing of an eye vergence –angle between two eyes

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Accommodation (one eye) lens changes shape to focus on objects –rounder for near object –flatter for far objects limitation: depth between 20cm and 2m

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Eyes fixate on object - rotate inwards if near by Eyes fixate on object - less rotation if far away Vergence (two eyes)

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Vergence difference from binocular stereopsis –angle of eyes rather than different images limitation: depth less than 3m

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Complications, complications… 1.Illumination (intensity, hue, motion) 2.Projection (3D world to 2D images) 3.Fragmentation (occlusion)

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Fragmentation objects connected in world –not always connected in image on retinas determine which patches in image belong together Visual completion A B

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Visual completion (fragmentation) Two abilities –modal completion: completion of pieces fragmented by occluders in world –blindspot completion: completion of visual image fragmented by existence of blindspot

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Modal completion handle fragmentation due to external occluder

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Modal completion handle fragmentation due to external occluder

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Modal completion handle fragmentation due to external occluder

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Modal completion handle fragmentation due to external occluder

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Result: - pieces are linked when - edges intersect at >= 90° - there is a visible occluder but no “filling in” behind occluder Modal completion handles fragmentation due to external occluder

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Blindspot completion handles fragmentation due to blindspot in eye

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Information actually picked up What kind of completion occurs? Pattern of light on retina Blindspot completion

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Blindspot completion Result - area is filled in (limited) filling in includes –texture, complex patterns (but not text) –smooth transitions between colours, alignment, intensity, etc AB CD

2002/02/12PSYC202, Term 2, Copyright Jason Harrison Recovery of World Structure: Art and Image 1.Illumination (intensity, hue, motion) 2.Projection (3D world to 2D images) 3.Fragmentation (occlusion)