Vision Flashcards
Vision (operational definition)
process of light energy being transduced (converted; translated) into neural impulses that the brain interprets to produce perpetual experience of sight
Physical energy for vision
electromagnetic radiation (light waves)
Electromagnetic radiation definition
a collection of one or more photons (light particles) propagating through space as electromagnetic waves
Light travels in a combined ____ and ____ waveform
electric and magnetic
*electric (up or down)and magnetic field (left or right) are going in opposite directions but are going together
Wavelength
the distance from identical points in consecutive waves eg. crest to crest; trough to trough; halfway through to halfway through
Amplitude
what is it, what does it effect
the distance from origin to crest or from origin to trough; the size of the wave itself Large vs small
“how big wave”
-effects the brightness
Frequency
what is it, what does it effect
the number of waves that pass a point per unit in time; number of wavelengths in a given period
e.g. number of waves per second; one wavelength per second
“how many waves”
-affects perception of color
Larger amplitude, _____
Smaller amplitude, ______
brighter; dimmer
High frequency, _______
Low frequency, ______
lots of waves; less waves
blueish colors; reddish colors
What is light?
Physical energy in the form of electromagnetic radiation
Visible light
only a small portion of the range of electromagnetic radiation; only one in electromagnetic radiation that can be seen with the naked eye
what has the highest frequency in electromagnetic radiation
gamma rays
what has the lowest frequency in electromagnetic radiation
radio waves
Order from highest to lowest frequency for electromagnetic radiation
gamma rays, x-rays, UV, visible light (purple to red; rainbow backwards); Infrared; radio waves
Sclera
What is it; function; external or internal
External anatomy of eye
“whites” of the eyes (protective outer layer)
Iris
what is it; function; external or internal
External anatomy of eye
the most visible part of the eye
-regulates amount of light that enters the eye
-color is determined by amount of pigment (melanin) in eye (low pigment = lighter iris
higher pigment= darker iris)
Pupil
What is it; function; external or internal
External anatomy of eye
black circular opening in the middle of the iris
1) constricts
-allows less light in but sharpens the image falling on the retina
2) dilates
-allows more light in but image is less sharp
Cornea
What is it; function; external or internal
External anatomy of eye
- transparent layer forming the front part of the eye
- protects eye and helps refract (bend; not reflect) the light
Lens
What is it; function; external or internal
Internal anatomy of eye
- transparent structure behind the iris
- helps refract the light on the retina by changing shape
Retina
What is it; function; external or internal
Internal anatomy of eye
- neural tissue lining the internal back surface of the eye
- absorbs light, processes images, and sends visual info to brain (optic nerve)
Fovea
What is it; function; external or internal
Internal anatomy of eye
-center of retina; best visual acuity (sharpness of vision)
Optic nerve
What is it; function; external or internal
Internal anatomy of eye
- bundle of nerve axons exiting the back of the eye
- transmits visual information from the eye to brain
- causes to have blind spot in our vision
why is there a blind spot in optic nerve
there is no photoreceptors
Photoreceptors
where are they found, what are they
retina contains specialized sensory receptor cells (PHOTO-receptors) that are sensitive to light
1) rods
- vision in dim light; peripheral vision; FOUND ONLY in peripheral retina
2) cones
- vision in bright light, color vision, fine details; highest concentration in fovea
Journey of light
1) rays of light enter the eye through the cornea, where they are partly bent (refracted)
2) move through the pupil which keeps extra light out
3) the rays of light pass through the transparent lens, which changes shape in order to fine-focus the image (accommodation )
4) light continues through the fluid matter, vitreous humor, within the eyeball and shines an upside down image onto the retina lining
5) light rays fall on retina, which processes and converts incident light to neuron signals using rod and cone cells
6) optic nerve sends to brain
What did Young & von Helmholtz discover?
Trichromatic theory of color
- discovered the retina contains three types of color receptors (cones)
1. blue (short)
2. green (medium)
3. red (long) - the light stimulation of these colors in varying combinations produces the perception of all visible colors
e. g stimulating red and green cones on retina causes us to perceive yellow
What did Edwald Hering discover?
Opponent process theory of color
-he noted that some color combinations we never see
(reddish-green, yellowish blue)
-argued that light is processed in an opponent manner
-some color pairs are processed the same neural pathway
-Photoreceptors can only process one color in each pathway at a time
-when one is activated the other is inhibited
What are the pairs of opposing color responses
red-green
yellow-blue
white-black
What happens when you stare at one color too long according to the opponent process theory?
causes photoreceptors to become fatigued
-when the color is removed, the opposing photoreceptors are free to fire along the same pathway and leads to the perception of after images
Trichromatic theory vs opponent process theory
Which one is correct?
both to a certain extent
trichromatic theory is correct in a sensory receptor level: some cones are sensitive to red, some to green, some to blue
Opponent process theory is correct in neural processing level: as the signal travels from the visual receptors in the occipital lobe, some neurons are activated by one color (red) and deactivated by different color (green) and then they compensate
