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PSYB51H3 Lecture Notes - Zonule Of Zinn, White Spot, Ganglion Cell

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PSYB51 Lecture 2
- What kind of psychophysical methods exist? Mention at least four. Describe one of them
in more detail.
o Method of limits
o Signal detection theoy
o Cross modality matching-perceived intensity of sound and match that by adjusting
souce of light(comparing apples and oranges sort of thing) Magnitude estimation
o Method of constant stimuli
o Method of adjustment
- Receptive fields: the ability of a neuron to respond to physical stimuli directly or
indirectly, within a constraint field of space
- Filters: retina filters different types of information, perception is filtering out information
to tell whether something is there or not
- Contrast- is filtered out in retina, difference in luminance which is more important info
than absolute levels of luminance
- Light: electromagnetic waves ; a steam of photons, tiny particles that each consist one
quantum of energy
o Can be either wave or little particle(both), depends on situation when these
metaphors work or don’t
o Light as photons when it hits a surface and absorbing while it’s good to talk of
light as a wave when it is travelling
o Light is a small range(tiny fractions) of electromagnetic range of a large
o Short spectrum of visible light from red to blue
o Colour is something that is created by the visual system
- Light can be absorbed, diffracted, reflected, transmitted or refracted
- Absorbed: energy(e.g. light) is taken up and not transmitted at all
o E.G. dust, surfaces, filters
- Diffracted: bent, or having waves that are spread out (e.g. waves of sound or light as they
encounter an obstacle, e.g., pass through a narrow aperture, they bend... first picture, )
o Sunlight passes through a tree, light gets bend and different wave lengths get bend
differently that is why you see them spread out
- Reflected: energy that is redirected when it strikes a surface
o Purkinje reflections
4 different surfaces in which light gets reflected(outer/inner surface of
cornea, outer/inner surface of lens)
These reflections viewed from front looks like little spots, measure the
positions of the light spots in camera and you can determine where the
eyes are actually looking
o Eye movements

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- Transmitted: energy that is passed on through a surface(when it is neither reflected nor
absorbed by the surface)
o Example: solar panels car with these panels absorbs light energy and transforms
it to electrical energy
- Refracted: Energy that is altered as it passes into another medium(e.g. light entering
water from the air)
o The two mediums must have two different densities, this difference determines
the degree to which refraction occurs
o Depth of a swimming pool
o Rainbows colourful because light gets bend when it hits surface
o Eye glasses, the eye itself
- Why is sensing light a “good idea”?
o You want to recognize those who are your enemies and those who are your
o You can avoid danger
o You can decide whether something is impt to you
o Light and being tired
You know when to sleep
Light determines whether or not we are getting sleepy or not
Circadian rhythm
If you are awake for a long time, you will get tired; but there is also a
clock that is adjusted by light (cycle)
- Special photoreceptor in eyes to provide brain with info about what kind of light there is
(day or evening, night or morning)
- Trees can also sense light
o Photosynthesize, some trees shed leaves, they can sense what time of year it is
(fall or summer for example)
- Evolution of eye
o Eye spots-very primitive eye movements, some protein on singular cell that
senses light
o Light sensitive protein: opsin
o If you have multiple cells, you can have nerve fibers(pass info from sensory
transduction that pass onto something else) and photoreceptors, some animals just
have that, all photoreceptors will get light from anywhere on that side of body,
and all photoreceptors will get same information, not very detailed very blurred
o To achieve more spatial vision good idea to have some kind of depressed/folded
area that allows limited directionality so light can only come from certain
directions hitting only certain photoreceptors ; important for animals that need to
perceive objects

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Light coming from above would hit the photoreceptors of bottom of eye; light
from below hits to part; light from above will not hit the receptors at the top
you get more specific info about where light is coming from
But still not very accurate, same sort of light will spread across larger
regions so vision is still blurred
o When aperture in front of eye is smaller(pin hole)
Pinhole eye allows finer directional sensitivity and limited imaging c
Light coming from some source will only hit certain part of retina, and
stimulate photoreceptors only in that part, light that comes from same
source but goes different direction will be prevented from hitting that part
of retina
A water filled cavity in eye, you might get infections
o Close the cavity, transparent humor develops in enclosed chamber so it prevents
bacteria, cornea(transparent membrane) also ensures the liquid is same density
which is important for refraction
o Distinct lens develop, the smaller the pinhole is the less light that gets in so you
won’t be sensitive to lower level to light, so larger aperture and have things
spatially resolved would be to have lens
o Transparent humour develops in enclosed chamber
o Distinct lens develops
You get spatial vision
Spherical eye sclera gives it shape
o Iris and separate cornea develop
- Eyes is not so durable, affected by age , 8 years you lose the acuity of eyes (loses its
o Eyes surrounded by sclera(white stuff)
o Cornea- light passes through it
o Inside eyes is lens which is hooked to ciliary muscles which are connected to
zonules of zinn(sac in which lens is embedded)
o iris makes eye colourful, ring shaped muscle that constricts to make pupil
o Pupil is nothing, just a hole, aperture
o The iris, lens, ciliary muscle, etc divide eye into 2 chambers: aqueous humor is
the front chamber, aqueous is water, called humor(comes from Greek word for
fluid, 4 fluids of body, if you have a good balance of this then you have good
humor), aqueous humor provides cornea(living membrane, consists of cells, nerve
endings, blink reflex)
o Lens itself doesn’t regenerate, less elastic as you age
o Vitreous humor, egg white, gel like, creates a pressure that makes eye’s shape
round, inflates the eye to its form
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