PSYB51H3 Lecture Notes - Vitreous Body, Aqueous Humour, Scotopic Vision

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22 Nov 2012
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PSYB51
Lecture 2
SAQ: Which kinds of psychophysical methods exist? Mention at least four. Describe one of
them in more detail.
- Signal detection theory not really
- Cross modality matching
- Magnitude estimation
- Method of constant stimuli
- Method of limits
- Method of adjustment
Method of cross modality matching: having stimuli like sound and light being presented at the
same time
- perceive magnitude of a sound and match it with another modality.
One of the retina’s job is FILTERING to tell whether something is there or not
Light
- Is electromagnetic waves
- Is both a wave and a tiny particle
- Use metaphor of wave when light is “trapping” energy
- Use light as a particle when thinking of it as a photon, when it is hitting a surface and
being absorbed; resulting in sensory transduction
- It is the small range of electromagnetic waves
Light can be:
- Absorbed: energy that is taken up and not transmitted at all. Eg, dust, surfaces, filters (to
some extent, they absorb light)
- Diffracted: happens whenever waves pass through an aperture or encounter some sort of
an obstacle; bending of light or having waves that are spread out
o Eg. When you take a photo or when looking at the sun and there is a rainbow
- Reflected: energy that is redirected when it strikes a surface
o Eg. The ways light gets reflected by the cornea
- Transmitted: energy that is encountering a surface and is transmitted in some form that
is not called reflection of absorption
o Eg. Getting transformed into electrical energy
- Refracted: when energy is altered as it passes into another medium
o Eg. When a pencil is put in water it looks as if it is bended
o Depth of a swimming pool looks shallower than it is
o Rainbows are colorful because light enters a drop of water and the light gets bent
as it hits the surface. Then turns into reflection
o Refraction is necessary for eye glasses
The Human Eye
Why is sensing light a “good idea”?
- You can find food, gives information about nutrition, helps perceive possible dangers,
circadian rhythm: can recalibrate after travelling,
Evolution of the Eye
- Primitive mechanisms of eye sensing: eye spots
o A single protein or cluster on single cells
- if you have the setup with a line of photoR and nerve fibres photoreceptors receive
light from everywhere. Everything is completely blurred; not very detailed information
- to achieve more spatial vision, it’s a good idea to have a folded area that limits
directionality so light can only come from certain directions and not others. The same
source of light will still spread light over a large region, so vision is still blurred
- “Pinhole” area
The human eye is made up of various parts:
- Eye is as big as a quarter, but not as durable as a quarter; easily damaged and ages very
easily
o Aging with vision begins to kick in (peak of its abilities) 8 years
o After 8 years you being to lose your acuity
o Lens starts to become sclerotic loses elasticity
- Lens attached to ciliary muscles + iris (ring shaped muscle to make pupil smaller
pinhole mechanism), pupil (piece of our body that is just a hole)
- Divided into 2 chambers
- Aqueous & vitreous humor: vitreous = gel like, inflates the eye
- Light is reflected, passes through cornea and gets refracted (has higher density than air)
o When jumping in water and opening eyes, it is blurry because its refractive index
is much higher than that of our cornea
- Pinhole mechanism also helps with vision without refraction
- People that are near sighted when walking into dark room, it is a little blurry
Refraction
- 4 diff optical components that modulate refraction: cornea, aqueous humor, lens, vitreous
humor
- Accommodation: biggest part of refraction
o Constant
- When something is closer to your eye, need more refraction cornea can’t help; glasses
and contacts can help
- The lens adds to refraction; the fatter it is, the more refractive power it has
- When you have a stretched lens (because ciliary muscles are relaxed, make aperture
larger)
- When cilliary muscles contract, the aperture gets smaller and the lens relaxes more into
its natural state
No problems with refraction:
a) Emmetropia: no problems with refraction; far light is being bent into a single point
b) Myopia: when the eyeball is longer than what refraction is able to
o Can be corrected with a concave lens
c) Hyperopia: corrected with convex lens, refraction power is too strong because eye is too
small
d) Astigmatism: cornea is not exactly spherically shaped; light does not get focused
properly; gets focused in spots
Ophthalmoscope
- A way at looking inside of the eye
- There is a single spot where everything goes in and out of the eye optic disk
- Hole in retina where we cannot see anything blind spot
- Dark spot = macula (means spot)
o Macula is where there is a high density of cones
- Neurons of the retina travel to the midbrain, therefore retina is part of the brain
- Fundus = back of the eye where the retina is
- Fovea has the highest density of photoR but is the thinnest area of the retina
Optic disk
- Place where ganglion cells, axons and blood vessels enter and exit the eye
- Situated on the nasal side of the fovea
- Left eye blind spot on left side; right side on right eye
- When something is in blind spot, gets filled in with the background/context of picture
Physical light travels through many areas, transduction happens in photoreceptors
Photoreceptors: first step of transducing physical things into neural signals
- 2 types:
o Rods
More specialized for scotopic vision nighttime