psych 2220 sensation & perception i lecture 3. keywords for lecture 2 air-dwelling eye,...
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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