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. transient cells sustained cells magnocellular layers of LGN parvocellular layers of LGN DORSAL VENTRAL

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.

visible invisible Spatial Frequency Threshold contrast CONTRAST SENSITIVITY FUNCTION Contrast sensitivity low high low

Low spatial frequency High High contrast Low THE CONTRAST SENSITIVITY FUNCTION

Low spatial frequency High High contrast Low stationary moving

.. 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

Artist’s cues Stereopsis Parallax Perspective Size Overlay Texture gradient Accommodation and convergence Cues to DEPTH

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

Perspective and overlay cues

overlay > perspective perspective > size overlay > size

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

EMMERT’s LAW If retinal image stays the same then perceived size will depend on distance small thing close big thing far

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

(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 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

overlay > perspective perspective > size overlay > size overlay > stereopsis stereopsis > perspective …but only at close distances

Pulfrich illusion

Parallax

parallax video

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

RIGHT EYE LEFT EYE FAR NEAR FAR CELL

RIGHT EYE LEFT EYE FAR NEAR NEAR CELL

NEAR FAR

… motion in depth leads us nicely into…. VISUAL MOTION

My mother by David Hockney

The scrabble game by David Hockney

Visual motion

Active motion of real image INFLOW OUTFLOWDATA Passive motion of real image Active motion of after image Attempt to move paralyzed eye Passive motion of after image No movement No movement PREDICTIONS No movement YES movement YES movement YES movement YES movement No movement EXPERIMENTS No movement YES movement

Active motion of real image INFLOW OUTFLOWDATA Passive motion of real image Active motion of after image Attempt to move paralyzed eye Passive motion of after image No movement No movement PREDICTIONS No movement YES movement YES movement YES movement YES movement No movement EXPERIMENTS No movement YES movement No movement YES movement YES movement No movement YES movement