# PSYB51H3 Lecture Notes - Lecture 2: Ophthalmoscopy, Retina, Sclera

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4 Mar 2011
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PSYB51
24th September, 2010
Lecture 2: The First Steps in Vision
Short Answer Question (Sample) ± on info learned from last lecture!
- Method of constant stimuli
- Method of Limits
- Magnitude estimation
------
- Light = an electromagnetic wave
- Very short spectrum of VISIBLE LIGHT (to humans)
- Colours is psychology [COLOUR PERCEPTION]
Æ In WHUPVRISK\VLFV ,7'2(617(;,67 (Colour is something that is
created by the visual system)
------
- Light can be absorbed, diffracted...: these principles apply to the entire
HOHFWURPDJQHWLFVSHFWUXPDOWKRXJKZOOEHIRFXVLQJRQ9ISIBLE LIGHT
1)
- Ex: shining light on a black surface = most of the light will be gone as in
ABSORBED
- Ex: Filters [ABSORB LIGHT!] = green/blue/yellow/red filters = these filters
only let through light of wavelength that we perceive as green/blue/yellow or
red respectively
- so all the other wavelengths are reduced Æ probably not completely
filtered out
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PSYB51
24th September, 2010
- so in a green filter: everythinJLVDEVRUEHGDQG³ILOWHUHG´RXWH[FHSWIRUJUHHQ
wavelengths [green light]
2) Diffracted:
- For waves of all sorts Æ LWGRHVQWKDYHWREHOLJKW
3) Reflected:
- Happens with mirrors and glass surfaces
- Happens on an object = some light absorbed while some is reflected
- Ex: brown deskÆ some brown[dark orange] wavelengths reflected back =
so you view desk as brown
- Purkinie eye-tracking system: these reflection on the eye
Î These reflections (P1 P2 P3...etc) arise from different optical surfaces of
the eye [outer and inner surface]
Î In total: 4 types of reflections on the cornea as well as on the lens behind
them
Î Now these reflection viewed from front Æthey look like little spots
Î So you measure the position of these light spots on your camera and then
you can determine the eye-position [where the eye is looking at]
4) Transmitted:
- Ex: Solar Panels = so it does not only absorb light energy but transforms it
to something else Æ ELECTRICAL ENERGY!
5) Refracted:
Ex: depth of pool Æ looks less deep than it really is!
- So what kind of information do we get from light?
Æ So vision helps us identify what we can or cannot eat and perhaps even
FIND it [FOOD] in the first place
ÆDifferentiate between different shapes [if you like bananas vs. Apples] =
so shape perception [you can do that with your eyes!]
ÆYou can recognize individuals [people] that are your friends and family
Æ<RXDOVRZDQWWREHDEOHWRUHFRJQL]H\RXU³HQHPLHV´-> e.g. unfriendly
dogs! = you want to be able to perceive DANGER!
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PSYB51
24th September, 2010
ÆSocial significance: you can perceive information about other people
RYTHYM
ÆTrees can also sense light: use light for PHOTOSYNTHESIS!
-some trees shed their leaves/change leaf colour = they can sense what time
of the year it is based on the light [e.g. to get ready for winter]
So you can decide whether something is important to you in whatever
ways:
- Whether you want to approach an object/individual or avoid it!
So, it makes sense to develop eyes [for humans]! But many other
animals have eyes as well.
Evolution of the eye:
Eye spots = you can already observe in single-cellular organisms
6RWKH\¶YHOLWWOHVSRWVRQWKHLUPHPEUDQHWKDWVHQVHOLJKW>,W¶VMXVWSURWHLQVWKRXJK Æ LW¶VTXLWH
different from what you have in the eyes]
- Just the regions of photo sensor cells = multiple cells that are just responsible for sensing
and you also have nerve fibres
- Obviously in single-cellular organisms ±> they have no nerves = they have just one cell!
- Cells that respond in some way to light = photoreceptors Æoften they have light-sensitive
protein [opsin]
- So information converted into neural signal and passed onto nerve fibres to some other
area [maybe CNS]
- In this picture: here the eye or what looks like an eye is on the surface of the skin
- The next step is to have this region of photoreceptors in some kind of a fold/cup
- Why does that make sense? It will limit the direction of light beams
- So light coming from above will hit photoreceptors at the bottom of that eye while the
opposite occurs for light coming from below
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## Document Summary

Short answer question (sample) on info learned from last lecture! Very short spectrum of visible light (to humans) in 907284158. 8% \$%\$% (colour is something that is created by the visual system) Light can be absorbed, diffracted: these principles apply to the entire. Ex: shining light on a black surface = most of the light will be gone as in. = green/blue/yellow/red filters = these filters only let through light of wavelength that we perceive as green/blue/yellow or red respectively. So all the other wavelengths are reduced probably not completely filtered out www. notesolution. com. So in a green filter: everythin8,-847-0/,3/19070/4:90. 0591477003 wavelengths [green light: diffracted: For waves of all sorts 9/40839,;094-09: reflected: Happens on an object = some light absorbed while some is reflected. Ex: brown desk some brown[dark orange] wavelengths reflected back = so you view desk as brown. Purkinie eye-tracking system: these reflection on the eye.

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