Module 4.2 - The Visual System Flashcards
light travels in waves that vary in terms of 2 different properties. what are these 2 properties?
length and amplitude
true or false: different species see different wavelength
true
what are the 3 characteristics of light
wavelength, amplitude, purity
in what 3 ways are the characteristics of light experienced by us?
hue, intensity and saturation
hue
colour of the spectrum
intensity
brightness
saturation
colourfullness or density
sclera
the white, outer surface of the eye
cornea
the clear layer that covers the front portion of the eye and also contributes to the eyes ability to focus
pupil
regulates the amount of light that enters by changing its size; it dilates (expands) to allow more light to enter and constricts (shrinks) to allow less light into the eye
iris
a round muscle that adjusts the size of the pupil; it also gives the eyes their characteristic colour
lens
a clear structure that focuses light onto the back of the eye
how does the lens focus light onto the back of the eye?
through the process of accommodation
retina
lines the inner surface of the eye and consists of specialized receptors that absorb light and send signals related to the properties of light to the brain
true or false: the retina consists of a single layer
FALSE: the retina contains a number of different layers
photoreceptors
specialized receptors found at the back of the eye; they send information to biopolar and ganglion cells
optic nerve
a dense bundle of fibres that transmit activity from the ganglion cells to the brain
optic disc
an area on the retina with no photoreceptors
blind spot
area on the retina with no photoreceptors
why are we not aware of our blind spot?
because the mind “fills in” the blind spot
rods
photoreceptors that occupy peripheral regions of the retina; they are highly sensitive under low light levels
what colours are rods most responsive to?
black and grey
what is the ratio of rods to ganglion cells?
10:1
cones
photoreceptors that are sensitive to the different wavelengths of light that we perceive as colour
where are the cones clustered?
around the fovea
fovea
the central region of the retina
what is the ratio of cones to ganglion cells
1:1
dark adaptation
the process by which the rods and cones become increasingly sensitive to light under low levels of illumination
trichromatic theory/young Helmholtz theory
colour ion is determined by 3 cone types that are sensitive to short (blue), medium (green) and long (red) wavelengths of light
what 3 colours are all other colours derived from?
red green and blue
opponent-process theory
a competing theory of colour vision, which assume that the visual system treat pairs of colours as opposing or antagonistic
opponent-process theory is consistent with _________
ganglion cells
colour blindness
total inability to distinguish colours
about ___% of all people are partly colour blind
4%
colour blindness is often caused by what?
when one type of cones contains the wrong proteins (e.g., “red ones” incorrectly contain the protein found in “green ones”)
near-sightedness/myopia
when the eyeball is slightly elongated, causing the image that the cornea and lens focus on to fall short of the retina
farsightedness/hyperopia
when the length of the eye is shorter than normal, causing the image to be focused behind the retina
feature detection cells
cells that selectively respond to simple and specific aspects of a stimulus, such as angles and edges
what are the 2 streams of vision
dorsal stream and ventral stream
dorsal stream
parietal lobe. visually guided movement. Patient DF
ventral stream
temporal lobe. object recognition. involved with recognizing things
prosopagnosia
face blindness
where does someone with prospagnosia have damage?
have damage to the right fusiform gyrus
perceptual constancy
the ability to perceive objects as having constant shape, size and colour despite changes in perspective
shape constancy
we see objects as having a constant shape even though the shape of the retinal image produced by an object changes when our point of view changes
location constancy
we perceive stationary objects as remaining in the same place even though the retinal image moves about as we move our eyes, heads, and bodies
size constancy
we see an object as having constant size even when its retinal image becomes smaller or larger (e.g., an approaching car is not actually growing)
brightness constancy
we see objects as having a relatively constant brightness even though the amount of light they reflect changes as the overall level of illumination changes
colour constancy
we see an object as maintaining its hue despite the fact that the wavelength of light reaching our eyes from the object may change as the illumination changes
binocular depth cues
distance cues that are based on the differing perspectives of both eyes
convergence
when the eye muscles contract so that both eyes focus on a single object; it typically occurs for objects that are relatively close to you
retinal disparity/binocular disparity
the difference in relative position of an object as seen by both eyes, which provides information to the brain about depth
monocular depth cues
visual cues to depth or distance that can be used by one eye alone
texture gradients
objects that are coarse and distinct at close range become fine and grainy at greater distances
light and shadow
the shadow cast by an object allows us to detect both the size of the object and the relative locations of objects. in addition, closer objects reflect more light than far-away objects
motion parallax
when an observer is moving, objects appear to move at different speed and in different directions
relative size
if 2 objects in an image are known to be of the same actual size, the larger of the 2 must be closer
heigh in plane
objects that are higher in our visual field are perceived as farther away than objects low in our visual field
linear perspective
parallel lines stretching to the horizon appear to move closer together as they travel farther away
interposition
nearby objects block our view of far-off objects, such as the umbrellas blocking the view of buildings behind them
