PSYCH 2220 Sensation & Perception I Lecture 3. Keywords for lecture 2 Air-dwelling eye, water-dwelling eye, (both: mask, powerful lens, flat cornea, pinhole),

PSYCH 2220Sensation & Perception I

Lecture 3

Keywords for lecture 2

Air-dwelling eye, water-dwelling eye, (both: mask, powerful lens, flat cornea, pinhole), presbyopia, astigmatism, accommodation, depth of focus, ophthalmoscope, retina, retinal blood vessels, fovea, optic disk, blind spot, retina,

cells, cell membrane, ions, potassium, sodium, channels(meaning 1), neurones, resting potential (-70mV), action potential, synapse, neurotransmitter, Schwann cells, axon, dendrites, polarization, depolarization,hyperpolarization,

dark/light adaptation, rods, thresholds, sensitivity, cones, visual purple, Purkinje shift, scotopic, photopic, fovea, receptive fields, bipolar cells, retinal ganglion cells

Eyemovements

Point eyesto rightplace

Accommodation

focus

PupilsLight

Adaptation

Adjust for the lightlevel

Transduction

Convertlight energyto activityin cells

Optic Disc

Fovea

The foveal pit

STRUCTURE OF THE EYE

pupil

cornea

retina

photoreceptorbipolar cell

retinalganglion

cell

LIGHT

lens

EXPANDEDVIEW

blind spot optic nerve

layerlayerlayerinner outermiddleto the blind spot

where this fibre willbecome part of theoptic nerve

The eye and its optics 4 - 1

RETINAL GANGLION CELLS

photoreceptors(rods or cones)

bipolarconnecting cells

retinal ganglion cells

The eye and seeing 5 - 6

Bipolar cell

CONVERGENCE

….. which means thereceptive field of aRGC is biggerthan a photoreceptor

photoreceptors(rods or cones)

bipolarconnecting cells

retinal ganglion cells

The eye and seeing 5 - 6

Bipolar cell

DIVERGENCE

….. which means thereceptive fields of RGCs overlap.

photoreceptors(rods or cones)

bipolarconnecting cells

retinal ganglion cells

The eye and seeing 5 - 6

ExcitatoryBipolar cell

InhibitoryBipolar cell

receptive field

spontaneous activity

photoreceptors(rods or cones)

bipolarconnecting cells

retinal ganglion cells

The eye and seeing 5 - 6

ExcitatoryBipolar cell

InhibitoryBipolar cell

OFF-CENTRE CELL

photoreceptors(rods or cones)

bipolarconnecting cells

retinal ganglion cells

The eye and seeing 5 - 6

ExcitatoryBipolar cell

InhibitoryBipolar cell

photoreceptors(rods or cones)

bipolarconnecting cells

retinal ganglion cells

The eye and seeing 5 - 6

ExcitatoryBipolar cell

InhibitoryBipolar cell

ON-CENTRE CELL

e

CONCENTRICALLY ORGANIZEDRECEPTIVE FIELDS

fovea

The eye and seeing 5 - 7

e

CONCENTRICALLY ORGANIZEDRECEPTIVE FIELDS

i i

i i ii

iiii

i

the receptive fieldof an OFF-CENTRE retinalganglion cell

the receptive field of anON-CENTRE retinalganglion cell

fovea

The eye and seeing 5 - 7

VIDEO from disc…

Look at how the cells will respond toan edge.

Followed by Sustained and Transient

video...

resp

on

se

1

2

21

3

3

4

4 5

5

space

response to spot in centre

response to spot in surround

spontaneous level

0

high

low

LIGHT DARK

Machbands

HI !

Types of Retinal Ganglion Cells

On-centreOff-surround

Off-centreOn-surround

Sustained transient

e eee

eeee

e i i

the receptive fieldof an OFF-CENTRE retinalganglion cell

e

e

i i ii

iiii

i eee

the receptive field of anON-CENTRE retinalganglion cell

Sustained transient

1 2 3 4

Perceptual effects that can beunderstood from knowing aboutretinal ganglion cells...

Machbands

Simultaneous contrast

Scallopillusion

Scallopillusion

luminance

MACH BANDS(seen on each side of an edge)

LUMINANCE PROFILES FOR PRODUCING ILLUSIONSDEMONSTRATING RETINAL GANGLION CELL

FUNCTIONING

“SCALLOPED” ILLUSION(edges seen, gradual change

part missed)

SIMULTANEOUSCONTRAST

(central areas which are thesame, seen as different)

GRADIENTS(can’t be easily detected)

Actual

Perceived

KEY

A light check in the shadow is the same gray as a dark check outside the shadow.

©1995, Edward H. Adelson

PHYSICAL PERCEPTUAL

luminance brightness

wavelength colour

Hermann Grid

less inhibition

RETINAL GANGLION CELLS

• Have spontaneous activity• show action potentials• can be inhibited by light• can be excited by light• have concentric fields• have smaller fields in the fovea

• (they also respond in an interesting and surprising way to colour, but we’ll come back to that when we look at colour)

INFORMATION GOING TO BRAIN

• is LIMITED (partial)• is ALREADY PROCESSED• is in the form of ACTION POTENTIALS• is DISTORTED (fovea more)• tells about EDGES (change)

Introduction to the structure of the brain

Cortex

THE OPTIC CHIASM

Left half of the brain needsinformation about the RIGHThalf of the visual field.

RIGHTVISUALFIELD

fixation point(foveas point here)

Left hemi-retina

RIGHT

FIELD

VISUAL

fixation point(foveas point here)

RIGHT

FIELD

VISUAL

OPTIC CHIASM

LEFT

FIELD

VISUAL

OPTIC CHIASM

RIGHT

FIELD

VISUALLEFT

FIELD

VISUAL

OPTIC CHIASM

LEFT RIGHTBRAIN BRAIN

DESTINATIONS OF THE VISUALPATHWAYS

1 Visual information is required for VISUAL REFLEXES aswell as PERCEPTION.

2 Three examples of visual reflexes are:

3 Perceptual pathway goes to the visual cortex via thethalamus (relay). The part of the thalamus that relays visualinformation to the visual part of the cortex is called theLATERAL GENICULATE NUCLEUS.

i PUPIL

ii FAST EYE

iii SLOW EYEMOVEMENT

regulates theamount of light inthe eye

changes where youare looking fromone place toanother

keeps the imagestable during headmovements andwalking

pupil controlcenter in brainstem

superior colliculus(swelling in themiddle of brainstem)

vestibular area(swelling at backof brain stem)

MOVEMENT

CONTROL

FUNCTION PURPOSE SITE IN BRAIN

The visual system 6 - 6

RIGHT

FIELD

VISUALLEFT

FIELD

VISUAL

OPTIC CHIASM

BRAIN STEM

THALAMUS pupil control centre

superior colliculus

vestibular area

DESTINATIONS OF THE VISUALPATHWAYS

1 Visual information is required for VISUAL REFLEXES aswell as PERCEPTION.

2 Three examples of visual reflexes are:

3 Perceptual pathway goes to the visual cortex via thethalamus (relay). The part of the thalamus that relays visualinformation to the visual part of the cortex is called theLATERAL GENICULATE NUCLEUS.

i PUPIL

ii FAST EYE

iii SLOW EYEMOVEMENT

regulates theamount of light inthe eye

changes where youare looking fromone place toanother

keeps the imagestable during headmovements andwalking

pupil controlcenter in brainstem

superior colliculus(swelling in themiddle of brainstem)

vestibular area(swelling at backof brain stem)

MOVEMENT

CONTROL

FUNCTION PURPOSE SITE IN BRAIN

The visual system 6 - 6

RIGHT

FIELD

VISUALLEFT

FIELD

VISUAL

OPTIC CHIASM

BRAIN STEM

THALAMUS pupil control centre

superior colliculus

vestibular area

Lateral geniculate nucleus of the THALAMUS

Organization of the lateral geniculateof the THALAMUS (1)

Parvocellularlayers (3- 6)

Magnocellularlayers (1- 2)

LEFT RIGHTBRAIN BRAIN

Injection of tracer to left eye

6655 44

3322

11 1122

334455

66

LATERAL GENICULATE NUCLEUS

1 Acts as a relay to the cortex

2 Keeps information from the two eyes separate

3 Has visual receptive fields that look just like the retina

4 Is retinotopically arranged

5 Is divided into layers:

1

2

3

4

5

6

LEFT RIGHT

gets input from RIGHT eye

gets input from LEFT eye

1,2 Magnocellular layers

3-6 Parvocellular layers

The visual system 6 - 8

(Magno = big)

(Parvo = small)

CORTEX

Magnification factorwhen looking at the centre, each letter uses

the same amount of cortex

David Hubel Torsten Wiesel

Plotting the receptive fieldof a simple cell…..

Hubel & Wiesel described three types of cells in the cortex:

• simple• complex• hypercomplex

from their responses all vision is built up.

They received a NOBEL PRIZE for this work.

CELL TYPES IN THE PRIMARYCORTEX:

SIMPLE CELLS

1 ... have receptive fields like this.

KEY:i= inhibitorye=excitatory

or or or

2 These fields could be made up from retinalcells like this:

ie

ie

Cortical cell

RECEPTIVEFIELDS

CELLS

ee

e

eee

e

e

e

ii

i

i

i

ii

i

i

i

ii

i iee

e

eee

e

e

e

ii

i

i

i

ii

i

i

i

ii

i i

WILL RESPOND

WILL NOT RESPOND('e' & 'i' regions stimulated).

SIMPLE CELLSare orientation tuned...

will respond equally well to any of these

ee

e

eee

e

e

e

iii

i

i

ii

i

i

i

ii

i i

ee

e

eee

e

e

e

ii

i

i

i

ii

i

i

i

ii

i i

ee

e

eee

e

e

e

iii

i

i

ii

i

i

i

ii

i iee

e

eee

e

e

e

iii

i

i

ii

i

i

i

ii

i i

ee

e

eee

e

e

e

i ii

i

i

ii

i

i

i

ii

i i

receptive field ofcomplex cell

receptive field ofcomplex cell

The visual system 6 - 13

Complex cells

receptive field

will not respond will respond will respond

The visual system 6 - 14