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
- Method of adjustment
- Magnitude estimation
- Light = an electromagnetic wave
- Very short spectrum of VISIBLE LIGHT (to humans)
- Colours is psychology [COLOUR PERCEPTION]
Æ In WHUPVRISK\VLFV ,7'2(61¶7(;,67 (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
- 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
- so all the other wavelengths are reduced Æ probably not completely
24th September, 2010
- so in a green filter: everythinJLVDEVRUEHGDQG³ILOWHUHG´RXWH[FHSWIRUJUHHQ
wavelengths [green light]
- For waves of all sorts Æ LWGRHVQ¶WKDYHWREHOLJKW
- 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
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]
- Ex: Solar Panels = so it does not only absorb light energy but transforms it
to something else Æ ELECTRICAL ENERGY!
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<RXDOVRZDQWWREHDEOHWRUHFRJQL]H\RXU³HQHPLHV´-> e.g. unfriendly
dogs! = you want to be able to perceive DANGER!
24th September, 2010
ÆSocial significance: you can perceive information about other people
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
- 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
6RWKH\¶YHOLWWOHVSRWVRQWKHLUPHPEUDQHWKDWVHQVHOLJKW>,W¶VMXVWSURWHLQVWKRXJK Æ LW¶VTXLWH
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
- 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
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.