2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002

1

Visual pathways

from here to there to everywhere

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 2

Imageon retina(as seenfrom backof eye)

Real world object

Pathways are between maps• maps maintain neighborhoodness and

local features (corners, lines, etc)• First map: retina a slightly distorted map

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 3

Each ganglion cell fires according to what is at its location

Area that each cell responds to is a receptive field

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 4

neighbouring cells in retina

respond to

neighbouring locations in image

visual map

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 5

Visual pathways

• path of visual information through brain• starts with ganglion cells• ends at cortical area• maps at LGN, V1, etc (LGN)

StriateCortex

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 6

What not to worry about• images in visual maps are distorted• images in visual maps are upside-down

this does not matter as long as• neighbours in image are also neighbours

in visual map

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 7

What can you do with a distorted upside down map?• determine edge orientations• determine line intersections (which and angle)• number of lines, motions of lines• regions, holes, patterns

Visual system determines structure of world

• measurements from maps• some knowledge (experience/evolution) of

world

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 8

How, What and Watch Out• How: parietal lobe

– LGN…V5/MT, action, spatial vision, visually guided behaviour

• What: temporal lobe– LGN…V3/4/8, object recognition, complex object

recognition– if damaged can produce action, but not perceive

location or orientation (Rama, pp. 63-)• Watch out: superior colliculus

– optic nerve…midbrain, orientation, “snake on your left?”, illumination changes

– processes auditory and tactile sensations too

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 9

How: parietal lobe -dorsal path• LGN…V5/MT, action, spatial vision, visually guided behaviour and

action• global movement

(LGN)

StriateCortex

V5/MT

Parietal Lobe

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 10

What: temporal lobe - ventral path• LGN…V3• object recognition through form and local

movement

(LGN)

StriateCortex

V3

Temporal Lobe

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 11

What: temporal lobe• LGN…V4…V8• object recognition through colour

(LGN)

StriateCortex

V4

Temporal Lobe

V8

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 12

Watch out: superior colliculus • optic nerve…midbrain: Tecto-fugal• receives ~20% of optic nerve fibers • more concerned with where a stimulus is than what• controls eye movements, detects objects located away from fixation and

guides eyes towards objects

(LGN)

Superior Colliculus

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 13

Watch out: superior colliculus • orientation of gaze and attention• “snake on your left?”, illumination changes• processes auditory and tactile sensations too

(LGN)

Superior Colliculus

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 14

Watch out: superior colliculus • passes on some information to parietal

lobe when V1 is destroyed– “blindsight” - unconscious sight

(LGN)

Superior Colliculus

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 15

Summary of pathways1. Object structure (“what I am seeing?”)

• located in temporal lobe; conscious?• form perception• colour perception

2. Movement (“how do I get this there?”)• located in parietal lobe; unconscious?• motion perception and planning

3. Preconscious reactions (“Aieee! Snake!?”)• Located in midbrain• Reacts to sound, touch: which direction is

danger?

2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 16

Summary of pathways

• All pathways operate separately, in parallel

• Question: how do we experience a unified world?