Psychology 2115A/B Lecture Notes - Chromatic Aberration, Scotopic Vision, Electromagnetic Spectrum

13 views7 pages
Published on 20 Apr 2013
School
Western University
Department
Psychology
Course
Psychology 2115A/B
Chapter 3 Review: Vision, Part 1
By the end of this section, you should know about:
- Slight and the eye
- Visual transduction
- Pigments and perception
Light
The quantum theory of light
o Quantum = particle of light
o Photon = 1 quantum
Intensity of light measured in photons
Smallest amount of light possible = a single photon of light
We measure light in terms of its intensity how bright it is, the number of photons present
The Electromagnetic Spectrum
Wavelength: the physical distance between the two highest peaks of a photon wave
Can be very short or very long
Very short and very long wavelengths of light are not visible to the human eye we are restricted to a
very small spectrum of light
Visible wavelengths of light correspond to a small portion of the entire electromagnetic spectrum
The longer the wavelength, the more red they appear to be
The shorter they are, the more blue/purple they appear to be
Greens and yellows in the middle
The Structure of the Eye
o Eyeball contained in the eye socket: a protective bony socket
o The cornea: Primary visual element that does almost all of the bending of light
Approximately 13mm in diameter, very transparent, contains no blood vessels, contains many
nerve endings
Functions to serve as a fixed lens
Responsible for gathering light and concentrating it so that it gets into the eye
Bulges forward form the eyeball football shaped
This bulging allows reception of light from slightly behind your eyeball allows you to see
slightly behind where your eye is
o Aqueous humor: transparent liquid that fills the chamber behind the cornea
o Pupil: a whole bounded by two membranes (iris)
Iris is a coloured membrane that surrounded the pupil
Can contract and expand depending on how big the whole needs to be
Iris membrane forms a ring around the hole (pupil) itself
The muscle in the iris is a dilator muscle
Controlling the amount of light that can enter the eye
o Lens: contain no blood vessels or nerves
Slightly yellow and gets more discoloured as we get older
Observed about 10% of the light that is allowed to enter the eye
Held in place by cilliary muscles that allow the lens to move in particular ways changes the
shape of the lens
o All of these elements of the eye are all trying to focus the light onto the back of the eye where the
retina is
o Vitreous humor: liquid that keeps the eyeball relatively round
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The Optical Elements of the Eye
Cornea refracts light the most
o Hits the cornea, goes through the pupil, hits the lens, accommodates the signal onto the retina
The changing shape of the lens provides fine focus, allowing us to focus from infinity to as close as
10 cm
Slightly yellow to correct for chromatic aberration
o Everything looks a little yellow in order to correct for the slight aberration in the environment
o Chromatic aberration makes you not able to see colours as well because the eye is yellowing
o Visible spectrum runs from 300-1600 nanometers in wavelength
The Pupil
Limits the amount of light that enters the eye
Diameter ranges from 2-8 mm
Small pupil size reduces image degradation, by increasing depth of field
Optimal pupil size is 2-3 mm
The pupillary reflex: automatic reflexive response that makes the two pupils equivalent in size at all
times
The Lens
Located directly behind the pupil and iris
Critical for bringing an image into focus on the retina
o Without the lens, vision is difficult and focused vision is impossible
The lens is relatively relaxed when the object is far
When the object is closer, the lens becomes much tighter
Accommodation
The process by which the lens varies its focus
When lens is spherical (increased curvature), near objects are in focus
When lens is flattened (decreased curvature), far objects are in focus
Near point: distance at which the lens can no longer adjust to bring close objects into focus
o Presbyopia: are related condition where there are changes in the near point where reading is not
at a comfortable distance
o Occurs because the muscles that are controlling the flatness and roundness of the lens are getting
stiff
Far point: distance at which a spot of light becomes focused on the retina
Optical Defects
Emmetropic eye
o Normal eye shape
o Image focused on the retina
Hyperopic eye: ‘far sighted
o Eyeball too short
o Near objects do not focus on the retina
Myopic eye: ‘near sighted’
o Eyeball too long
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