Transcript lecture 3

PSYCH 2220
Sensation & 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
Eye
movements
Point eyes
to right
place
Accommodation
focus
Pupils
Light
Adaptation
Adjust for
the light
level
Transduction
Convert
light energy
to activity
in cells
Fovea
Optic
Disc
The foveal pit
STRUCTURE OF THE EYE
lens
retina
pupil
EXPANDED
VIEW
cornea
blind spot
optic nerve
retinal
ganglion
cell
bipolar cell photoreceptor
LIGHT
to the blind spot
where this fibre will
become part of the
optic nerve
inner
layer
middle
layer
outer
layer
The eye and its optics 4 - 1
RETINAL GANGLION CELLS
photoreceptors
(rods or cones)
Bipolar cell
CONVERGENCE
bipolar
connecting cells
retinal ganglion cells
….. which means the
receptive field of a
RGC is bigger
than a photoreceptor
The eye and seeing 5 - 6
photoreceptors
(rods or cones)
Bipolar cell
DIVERGENCE
bipolar
connecting cells
retinal ganglion cells
….. which means the
receptive fields of
RGCs overlap.
The eye and seeing 5 - 6
photoreceptorsreceptive field
(rods or cones)
Excitatory
Bipolar cell
Inhibitory
Bipolar cell
bipolar
connecting cells
retinal ganglion cells
spontaneous activity
The eye and seeing 5 - 6
photoreceptors
(rods or cones)
OFF-CENTRE CELL
Excitatory
Bipolar cell
Inhibitory
Bipolar cell
bipolar
connecting cells
retinal ganglion cells
The eye and seeing 5 - 6
photoreceptors
(rods or cones)
Excitatory
Bipolar cell
Inhibitory
Bipolar cell
bipolar
connecting cells
retinal ganglion cells
The eye and seeing 5 - 6
photoreceptors
(rods or cones)
ON-CENTRE CELL
Excitatory
Bipolar cell
Inhibitory
Bipolar cell
bipolar
connecting cells
retinal ganglion cells
The eye and seeing 5 - 6
CONCENTRICALLY ORGANIZED
RECEPTIVE FIELDS
fovea
e
The eye and seeing 5 - 7
CONCENTRICALLY ORGANIZED
RECEPTIVE FIELDS
the receptive field
of an OFF-CENTRE retinal
ganglion cell
i i
fovea
i
i
i
i
e i
i i i i
the receptive field of an
ON-CENTRE retinal
ganglion cell
The eye and seeing 5 - 7
VIDEO from disc…
Look at how the cells will respond to
an edge.
Followed by Sustained and Transient
video...
i i i
i eee i
i
i
i i
LIGHT
2
DARK
i i i
i eee i
i
i
i i
the receptive field of an
i i i
ON-CENTRE retinal
receptive field of an
i i i ganglion cell i ee
i i i
-CENTRE retinal
e i
i eee i
i eee i
i
nglion cell
i
i
i
i
i
i
i
i i
i i
the receptive fieldi ofian
i the receptive field of an
the receptive field of an ON-CENTRE iretinal
e
e e i ON-CENTRE retinal
ganglion cell
ON-CENTRE retinal
i ganglion cell
i
ganglion cell
i i
3
5
1
4
the receptive field of an
ON-CENTRE retinal
ganglion cell
response
high
response to spot in centre
spontaneous level
space
1
low
0
2 3 4
5
response to spot in surround
Mach
bands
HI !
Types of Retinal Ganglion Cells
On-centre
Off-surround
i i i
i eee i
i
i
i i
the receptive field of an
ON-CENTRE retinal
ganglion cell
Sustained
1
transient
2
Off-centre
On-surround
the receptive field
of an OFF-CENTRE retinal
ganglion cell
e ee
e i i e
e
e
e e e
Sustained
3
transient
4
Perceptual effects that can be
understood from knowing about
retinal ganglion cells...
Mach
bands
Simultaneous contrast
Scallop
illusion
luminance
Scallop
illusion
LUMINANCE PROFILES FOR PRODUCING ILLUSIONS
DEMONSTRATING RETINAL GANGLION CELL
FUNCTIONING
MACH BANDS
(seen on each side of an edge)
SIMULTANEOUS
CONTRAST
(central areas which are the
same, seen as different)
KEY
Actual
Perceived
“SCALLOPED” ILLUSION
(edges seen, gradual change
part missed)
GRADIENTS
(can’t be easily detected)
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
i i i
i eee i
i
i
i i
i i ofi an
the receptive field
i retinal
eee i
ON-CENTRE
i
ganglion celli
i i
the receptive field of an
ON-CENTRE retinal
ganglion cell
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
RIGHT
VISUAL
FIELD
Left half of the brain needs
information about the RIGHT
half of the visual field.
fixation point
(foveas point here)
RIGHT
VISUAL
FIELD
Left hemi-retina
fixation point
(foveas point here)
RIGHT
VISUAL
FIELD
OPTIC CHIASM
LEFT
VISUAL
FIELD
OPTIC CHIASM
LEFT
VISUAL
FIELD
RIGHT
VISUAL
FIELD
OPTIC CHIASM
LEFT
BRAIN
RIGHT
BRAIN
DESTINATIONS OF THE VISUAL
PATHWAYS
1 Visual information is required for VISUAL REFLEXES as
well as PERCEPTION.
2 Three examples of visual reflexes are:
FUNCTION
PURPOSE
i PUPIL
CONTROL
regulates the
amount of light in
the eye
ii FAST EYE
MOVEMENT
changes where you
are looking from
one place to
another
iii SLOW EYE
MOVEMENT
keeps the image
stable during head
movements and
walking
SITE IN BRAIN
pupil control
center in brain
stem
superior colliculus
(swelling in the
middle of brain
stem)
vestibular area
(swelling at back
of brain stem)
3 Perceptual pathway goes to the visual cortex via the
thalamus (relay). The part of the thalamus that relays visual
information to the visual part of the cortex is called the
LATERAL GENICULATE NUCLEUS.
The visual system 6 - 6
LEFT
VISUAL
FIELD
RIGHT
VISUAL
FIELD
OPTIC CHIASM
THALAMUS
BRAIN STEM
pupil control centre
superior colliculus
vestibular area
DESTINATIONS OF THE VISUAL
PATHWAYS
1 Visual information is required for VISUAL REFLEXES as
well as PERCEPTION.
LEFT
VISUAL
FIELD
2 Three examples of visual reflexes are:
FUNCTION
PURPOSE
i PUPIL
CONTROL
regulates the
amount of light in
the eye
ii FAST EYE
MOVEMENT
changes where you
are looking from
one place to
another
iii SLOW EYE
MOVEMENT
keeps the image
stable during head
movements and
walking
RIGHT
VISUAL
FIELD
SITE IN BRAIN
pupil control
center in brain
stem
OPTIC CHIASM
superior colliculus
(swelling in the
middle of brain
stem)
vestibular area
(swelling at back
of brain stem)
3 Perceptual pathway goes to the visual cortex via the
thalamus (relay). The part of the thalamus that relays visual
information to the visual part of the cortex is called the
LATERAL GENICULATE NUCLEUS.
The visual system 6 - 6
THALAMUS
BRAIN STEM
pupil control centre
superior colliculus
vestibular area
Lateral geniculate nucleus of the THALAMUS
Organization of the lateral geniculate
of the THALAMUS (1)
Parvocellular
layers (3- 6)
Magnocellular
layers (1- 2)
6
6
54
5
4
3
3
2
1
Injection of
tracer to left eye
2
1
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:
6
5
4
3
2
1
LEFT
gets input from RIGHT eye
gets input from LEFT eye
RIGHT
1,2 Magnocellular layers
(Magno = big)
3-6 Parvocellular layers
(Parvo = small)
The visual system 6 - 8
CORTEX
Magnification factor
when looking at the centre, each letter uses
the same amount of cortex
David Hubel
Torsten Wiesel
Plotting the receptive field
of 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 PRIMARY
CORTEX:
SIMPLE CELLS
1 ... have receptive fields like this.
or
or
or
2 These fields could be made up from retinal
cells like this:
RECEPTIVE
FIELDS
ie
i
CELLS
e
Cortical cell
KEY:
i= inhibitory
e=excitatory
SIMPLE CELLS
are orientation tuned...
i
i
i
i
e
i e e
e
i
i e e
e
i
e
i
e i
i
i
i i
WILL RESPOND
i
i
i
e i
e
i
e e i
i e e
e
i
e
i
e i
i
i
i i
WILL NOT RESPOND
('e' & 'i' regions stimulated).
Complex cells
receptive field of
complex cell
will respond equally well to any of these
i
i
i
i
i
i i
i
e i
i e e
e
ii
i e ei
i
e i ee i
ei
i
e i
e ii e
i
ee
i i i i i e e ii
i
i
ei i e i
ee
ii i i e
e e i i i i ii e e i
e e ee i e e
e ii e
e e
ii e e i
i
e i e e
i e ii e i i
i i i e
i
e i i
ii i
i
receptive field of
complex cell
The visual system 6 - 13
receptive field
will not respond
will respond
will respond
The visual system 6 - 14