Transcript lecture 6
PSYCH 2220 Sensation and Perception I Lecture 6 Keywords for lecture 5 Dorsal/ventral streams, action/perception streams. Grandmother cell hypothesis. Face cells, hand cells (in ventral stream), prosopagnosia. Distributed processing. DORSAL transient cells magnocellular layers of LGN parvocellular layers of LGN VENTRAL sustained cells SPATIAL VISION FOURIER’S THEOREM: “any complex curve can be mathematically described as the sum of a series of sine waves” Variation of luminance across a scene can therefore be described as a series of sinewaves of different SPATIAL FREQUENCIES. Just low spatial frequencies…. … all spatial frequencies High spatial frequencies here are NOT telling you about the face but about the annoying squares…. …when the squares are too small to be seen, then the remaining information (i.e., the face) can be seen clearly. high low Contrast sensitivity Threshold contrast invisible visible low high Spatial Frequency CONTRAST SENSITIVITY FUNCTION High contrast Low THE CONTRAST SENSITIVITY FUNCTION Low spatial frequency High stationary High contrast Low moving Low spatial frequency High .. which revises… Big rfs best for low sf found in periphery Where cells prefer MOVEMENT (on way to dorsal stream good for action…) DEPTH PERCEPTION Cues to DEPTH Stereopsis Parallax Perspective Size Artist’s cues Overlay Texture gradient Accommodation and convergence David Hockney The Ame’s room as conflict between SIZE and PERSPECTIVE Ame’s room movie perspective vs size The IMPOSSIBLE TRIANGLE as conflict between PERSPECTIVE and OVERLAY (or OCCLUSSION) The playing card illusion as conflict between overlay and size b a 6 A Perspective and overlay cues perspective > size overlay > perspective 6 overlay > size A Size constancy: a given object seems the same size as its retinal image size varies with distance from the viewer. Mechanisms of size constancy can be clarified by looking at when it breaks down… 1 – Emmert’s Law 2 – Moon Illusion small thing close big thing far EMMERT’s LAW If retinal image stays the same then perceived size will depend on distance holding the screen closer makes the after image look smaller holding the screen further away makes the after image look bigger EMMERT’s LAW If retinal image stays the same then perceived size will depend on distance DEMO ONLY!! They have been MADE different sizes here!!) CRITICAL POINT: the moon always has the same visual angle, but different perceived distance. Scale demo (from Lord of the Rings) Binocular disparities and stereopsis left eye's view of a cube right eye's view of the same cube (red over left eye) The correspondence problem: How does the brain know which dots in the right eye go with which dots in the left eye? Floating Square RIGHT EYE right eye c a dot 'a' is seen by both a eyes dot b is seen only by b the left eye c dot 'c' is seen only by the right eye d b a left eye LEFT EYE (red over left eye) Reversing the glasses opposes stereopsis and artist’s cues Necker cube Cube Pyramid (lots of depth) (red over right eye) Checkerboard AUTOSTEREOGRAM Ame’s Window Demonstration perspective > size overlay > perspective 6 overlay > size A overlay > stereopsis stereopsis > perspective …but only at close distances Pulfrich illusion a b dark glass to adapt (and slow down) the right eye c right eye left eye b a Parallax parallax video Accommodation and convergence Accommodation and convergence need someone who hasn’t got stereopsis parallax doesn’t know about artist’s cues: (perspective, overlay, texture gradients,size) who could this be??? Accommodation cues can be used to solve the visual cliff. Neural basis of stereopsis Ocular dominance bands FAR CELL RIGHT right EYE eye 1 a FAR f b NEAR left EYE eye LEFT 2 3 NEAR CELL RIGHT right EYE eye 1 a FAR f b NEAR left EYE eye LEFT 2 3 NEAR FAR right eye some cells will respond to movement in the direction of the filled arrows, but not in the direction of the open arrows. left eye … motion in depth leads us nicely into…. VISUAL MOTION My mother by David Hockney The scrabble game by David Hockney Visual motion EXPERIMENTS PREDICTIONS INFLOW OUTFLOW DATA Active motion of real image No movement No movement Passive motion of real image No movement YES movement Active motion of after image YES movement YES movement Passive motion of after image YES movement No movement Attempt to move paralyzed eye No movement YES movement EXPERIMENTS PREDICTIONS INFLOW OUTFLOW DATA Active motion of real image No movement No movement No movement Passive motion of real image No movement YES movement YES movement Active motion of after image YES movement YES movement YES movement Passive motion of after image YES movement No movement No movement Attempt to move paralyzed eye No movement YES movement YES movement