Perception 2 Flashcards
Visible light
Band of energy within the electromagnetic spectrum
Visible light wavelengths from
400-700nm
Different wavelengths of light are associated with different ____ ____
Color perceptions
Photons
Small pockets of energy that light consists of
Luminance
Number of photons per unit space
Absorption
As photons collide with particles of matter
Reflection
As light strikes opaque surfaces
Transmission
Light passes through transparent matter
What do simple chambered eyes use to project an image onto the retina
Convex cornea and lens
The human eye enables ____, which can represent the spatial structure rather than sum total of light
Directional sensitivity
_____ transduce light into an electrical potential
Photoreceptors
Retinal ganglion cells
Where visual signals flow through a network of neutrons to, and then out the back of the eye via the optic nerve
Two types of photoreceptors
Rods and cones
Rods are located
Primarily in peripheral retina
Rods are capable of
Operating in low light levels, and can detect a single photon
Cones are concentrated
In center of center of retina (fovea)
Cones require ____ light levels to respond
Higher
Cones have ____ different _____
3, photopigments
Cones are sensitive to ____, ____, and ____ wavelengths
Short, medium, and long
Visual pathway consists of
Retina -> optic nerve -> optic chiasm > LGN > primary visual cortex
Bottom up
The retina doesn’t simply record light intensifies, responses are shaped processes occurring within the retina, most notably light/dark adaptation and lateral inhibition
Top down
The brain also uses knowledge about how light interacts with objects when determining perceived brightness
Brightness constancy
When someone perceives something as the same colors in both situations
What causes brightness constancy
White color will reflect less light indoors than black color will reflect outdoors
Light dark adaptation
Sensitivity of retina changes to adjust to brightness, and is reduced when it’s too bright and increases when it’s not bright enough
Light dark adaptation makes it so the retina encodes _____
Contrast
Contrast
The ratio of an objects luminance relative to the mean or background luminance
Contrast plays a critical role in achieving
Brightness constancy
Light/dark adaptations can produce ____ under some circumstances
Illusions
Lateral inhibition
Early form of information processing in retina
Retinal ganglion cells receive both _____ and _____
Excitatory (+) and inhibitory (-)
Retinal ganglion cells are
Arranged in a center surround configuration across the retinal image
Lateral inhibition makes the visual system
Sensitive to changes in luminance
The sensitivity to changes in luminance caused by lateral inhibition can have
Dramatic effects on perceived brightness
Our visual system also uses knowledge of how _____ ____ with 3d objects when determining brightness
Light interacts
Why does the world appear devoid of color under low light conditions
Only rod photoreceptors, which contain a single type of photopigment, are sensitive enough to operate
Because light of different wavelengths and intensities can elicit identical responses, which
Makes it impossible to accurately signal different wavelengths
S cones
Cones that are preferentially sensitive to short wavelengths (blue)
M cones
Cones that are preferentially sensitive to middle wavelengths (green)
L cones
Cones that are preferentially sensitive to long wavelengths (red cones)
The relative outputs or the three cones allows
Unambiguous signaling of wavelength
Monochromacy
Complete color blindness which is caused by having either 0 or 1 functioning cone type; extremely rare
Dichromacy
Only 2 functioning cone types
Protanopia
Type of dichromacy; missing L cones; 1% males 0.02% females
Deuteranopia
Type of dichromacy; missing M cones; 1% males 0.01% females
Tritanopia
Type of dichromacy; missing s cones; 0.002% males, 0.001% females
Anomalous trichromacy is _____ ______ form of color perception deficiency
Most common
Anomalous trichromacy
Defect in one of the cone types
Protanomaly
L cone defect
Deuteranomaly
M cone defect
Tritanomaly
S cone defect
Ishihara Color Test
test for color blindness
Color opponency
Retinal ganglion cells receive excitatory + and inhibitory - input from different cone types
Color opponency can be demonstrated using ___
Negative afterimages
Our visual systems also try to achieve ____ by accounting for the intensity and composition of light hitting different surfaces
Color constancy
