Download lecture 2

PSYCH 2220
Sensation and Perception (I)
Lecture 2
Keywords for lecture 1
electromagnetic spectrum, (pit viper), mechanical energy,
chemical energy, stages of vision, (i) eye movements,
(ii) focus, (iii) light regulation, pupil, pin-hole camera,
refraction, focus, cornea, lens, accommodation,
myopia, hyperopia, astigmatism, presbyopia
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
SHORT SIGHTED
(Myopia)
DISTANT
OBJECT
eg. star
Even the relaxed lens is too strong. The rays are
focused in front of the retina!
DISTANT
OBJECT
eg. star
The CONCAVE lens makes the rays DIVERGE, thus
compensating for the unwanted strength of the eye's optics.
The eye and its optics 4 - 5
LONG SIGHTED
(Hyperopia)
CLOSE
OBJECT
The fully-contracted lens cannot get strong enough. The
rays are focused behind the retina!
CLOSE
OBJECT
The CONVEX lens helps the rays CONVERGE, thus
assisting the inadequate strength of the eye's optics.
The eye and its optics 4 - 6
With age, the lens becomes less flexible and accommodation becomes
fixed at some distance. This fixing of the focal length of the lens is
called PRESBYOPIA.
The refracting power of the eye may not be the same in all dimensions.
This is called ASTIGMATISM.
Side view
Flatter
Top view
For this person, the cornea is flatter from left to right than it is from
top-to-bottom. Therefore, for this astigmatic person, vertical lines
would be better in focus than horizontals.
Photo taken through
a LARGE aperture
shallow depth of
field
(only one distance is
in focus)
Photo taken through
a SMALL aperture
long depth of
field
(lots of distances are
in focus)
Most of the refraction
takes place at the
air/water boundary of
the CORNEA in the
air
Lens in the eye of
an AIR-LIVING
animal
AIR LIVING
No refraction takes place
at the water/water
boundary of the CORNEA
in the water
Lens in the eye of a
WATER-LIVING
animal
WATER LIVING
DIVING ANIMALS
1 put on a mask that keeps air in front of
cornea
2 rely on a STRONG lens that can
change from air-living to water living eg:
otter
Air Type
3 Have a FLAT cornea (to remove its
influence) and then use a WATER-LIVING
style lens eg. Penguin, flying fish
Water Type
4 Have two pairs of eyes - one for each
environment eg. Four-eyed fish
5 Use a WATER-LIVING style lens in the
water and bi-pass the cornea by using a
PIN HOLE pupil on land eg. seal
1. Diving mask
2.
strong
The Otter - who can change her
eye from .....
… Air Type
… to….
….Water Type
3. Flat cornea + fish-type lens
4. Four eyes (!)
Four-eyed fish
4. Four eyes (!)
5. Pin hole on land; fish-type in water
Human using the seal solution
Antony van Leeuwenhoek (1632-1723)
Leeuwenhoek’s
Microscope
Na+
nucleus
K+
cytoplasm
membrane
Potassium K+ (Latin Kalium)
Sodium Na+ (Latin Natrium)
extra-cellular
fluid
NERVE CELL
ONE WAY
synapse
voltage dependent
sodium channels
neurotransmitters
ACTION POTENTIAL
THE CELL CONCEPT
KEYWORDS:
Cell, membrane, cytoplasm, nucleus, extracellular fluid
ions, sodium, potassium, channels
electrode, voltmeter, microelectrode, resting potential
millivolt (1/1000 volt)
NERVE CELLS
sodium channels, action potential
axons, synapse, neurotransmitter, millisecond
VIEWER
SUBJECT
Half-silvered
mirror
How an OPHTHALMOSCOPE works
Optic
Disc
Fovea
RETINAL PROPERTY
1 Image upside down
2 image is very small
3 image on a curved
surface
4 TWO retinas
5 blood-vessel tree
PERCEPTION
>>>>>
>>>>>
seen right way up
world seen actual size
>>>>> no curve seen
>>>>> only ONE world seen
>>>>> no tree seen!!!
RETINAL PROPERTY
PERCEPTION
1 Image upside down >>>>> seen right way up
2 image is very small >>>>> world seen actual size
3 image on a curved surface >>>>> no curve seen
4 TWO retinas
>>>>> only ONE world seen
5 blood-vessel tree
>>>>> no tree seen!!!
6 BLIND SPOT (where the
nerve comes in ) has no
receptors
>>>>>
7 only the central part of the
retina is very sensitive >>>>>
no hole seen!
no difference in
clarity between
vision in different
parts of the field
Filling in
Visual memory test:
what letters are on the
‘4’ key?
So:
visual input is poor
visual memory is poor
therefore
vision is poor!
We are almost blind!!
Sometimes:
we see what is not there
do not see what is there
(Do we ever see what
IS there?! There might
be more to this
perception thing than
meets the eye..)
Adaptation
.. than this one.
.. than this one.
This one appears
brighter...
This one appears
dimmer...
Under PHOTOPIC CONDITIONS
but under SCOTOPIC CONDITIONS
Structure of eye and retina
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
cone
Rod
RECEPTIVE FIELD:
the area in which energy will have an effect
VISUAL RECEPTIVE FIELD:
the area in the outside world where light
will have an effect
THE VISUAL RECEPTIVE FIELD
OF A SINGLE PHOTORECEPTOR
The Visual Receptive Field
of a single photoreceptor.
Light outside this region
will have no effect on this
cell.
screen
a single rod
The foveal pit
Different
shape
Different
distribution
edge BLIND FOVEA
SPOT
edge
edge BLIND FOVEA
SPOT
edge
starts off bad
BAD
BAD
Different
sensitivity
starts off better than
rods
gets very good
doesn't improve much
GOOD
GOOD
time in dark
time in dark
GOOD
RODS
Different
pigments
BAD
BLUE
GOOD
CONES
RED
BAD
RODS
BLUE
CONES
RED
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