chapter 5- vision Flashcards
what is the law of specific nerve energies?
-the brain encodes information based on which neurons are active. its not based on the stimuli themselves but instead these neurons. if you touch your eyes you see things, if you stillmulated audio receptors you would hear
what is the centre of the iris
pupil
light enters centre of iris. the ____ . it is focused by ______ (adjustable) and ____ (not adjustable, and projected to the _____, the rear surface of the eye
pupil, … lens, cornea…retina
the visual system does not replicate images instead it
codes it by various neuronal activity
describe travel of light through the receptors
it first goes to receptors at the back of the eye, then to bipolar cells then to ganglion cells. the ganglion axons go to the back of the brain to the optic nerve. there are also amacrine cells which get information from bipolar cells and send it to other bipolar cells, amnicrane cells and ganglion cells
what do amnicrine cells do
refine the input to ganglion cells enabling certain ones to respond mainly to particular shapes, directions of movement, changes in lighting color and other visual features
what creates the blind spot
the axon join the optic nerve and it has no receptors
why don’t you notice blind spot
brain fills in the gap, anything in blind spot one eye is visible to the other eye
the fovea is the
central portion of the retina, tiny and specialized for acute specialized vision..it is so detailed because almost no blood vessels or ganglion axons
the more important part of seeing detail from the fovea is
each receptor connects to a single bipolar cell which connects to a single ganglion cell that has an axon to the brain
the ganglion cells in the fovea of humans are called
midget ganglion cells
why are they called midget ganglion cells
each is small and responds to a single cone , so each cone in the fovea has a direct route to the brain
vision is dominated by what you see in fovea because
midget ganglion cells provide 70 percent of the input to the brain
“eyes like a hawk” is a phrase because
birds have two fovea one looking ahead and one straight and their eyes are bigger
where do predatory birds have most receptors and why
top half because they spend most time looking down. input from bottom goes to top of the fovea
why can the brain not detect the exact location or shape of a peripheral light source? what advantage does it have instead
because towards to periphery more and more receptors converge onto bipolar and ganglion cells ..has sensitivity for dim light, perception of fainter things
in the peripehrary the ability to detect detail is limited by
inference by nearby objects
rods are in the ____ and for ___ light and cones are in the ___ and for ____
peripherally, dim…..fovea, color
are there more rods or cones ? what’s the ratio?
more rods..20:1
visible lights consists of electromagnetic radiation within the range
less than 400nm to more than 700nm
why do we call the wavelengths light
the receptors in our eyes are tuned to detecting them
what does trichromatic theory/young helmholts theory say about how we see color
we perceive color through the relative rates of response by three kinds of cones, each one maximally sensitive to a different set of wavelengths
how did hemholtz decide on three?
people could match any color by mixing appropriate amounts of just three wavelengths?
what happens when all 3 types of wavelengths are active
we see white or gray
which wave length cones are more abundant? because of this we its harder to see what dots
medium and long. blue
what is the difference in distribution of short medium and long wavelength cones
short is evenly while the other two are distributed haphazardly with differences among individuals .causes small differences. cones are so scarce in periphery no color vision there .
what is color constancy?
ability to recognize colours despite changes in lighting
why should we avoid talking about the color of a wave length of light?
a certain wavelength of light can appear as different colours depending on the background
explain retinx theory
combo of the words retina and cortex. the cortex is comparing information from different parts of the retina to determine the brightness and color for each area…
what was dale purves idea that was more general of the retinix theory
whenever we see something we make an inference…visual perception requires reasoning and inference not just retinal stimulation
explain opponent process theory
color vision works in pairs….red,green..yellow blue..white black….when you stare at a color it gets fatigurd…this is because cells in the retina for example one gets excited by short and inhibited by medium/ long…but if you stare at blue for two long that cell becomes fatigued and stops firing as much. you get a decreased response leading you to perceive yellow
why can opponent process theory not be the whole story
after images depend on the whole context, not just the light on individual receptors..the cerebral cortex must be responsible not the bipolar or ganglion cells
where does the dorsal stream go through
parietal cortex
what pathway is the dorsal stream
action, “how” because of importance for visually guided movements
what happened to the patient who had damage to her ventral pathway
she couldn’t see objects but she could put an envelop through slot but she could not say wether it was horizontal or vertical
what happens to patients with dorsal damge
they can identify objects they see while walking but not good at integrating vision with arm and leg movements so they bump into things
where is secondary visual cortex
just anterior to v1 in the occipital cortex
what is the difference between receptive feilds in v1 and v2
v2 receptive fields are elongated
cells of what area respond to corners, textures or complex shapes?
v2
which areas are highly sensitive to color and other the disparity between what the left and right eye sees
v2 and v3
true or false: both area v1 and v2 respond to lines, edges or sine wave gratings
true
cells in the _____ learn to recognize meaningful objects
inferior temporal cortex
monkeys responded about the same to mirrored images but not to _____..why?
figure- ground reversal..they and humans perceive it as a white object with black background
what happens after a bit of experience viewing an object vs at first?
at first the cell responds mainly to the angle it saw but after experience it responds almost equally to it at different angles regardless of major changes in the pattern that reaches the retina
what is a possible bases of object permanence?
monkeys saw an object then new or surprising one appeared. some cells in inferotemprol cortex when an original object objeread and other cells responded strongly to a new object
what is visual agnosia? explain how it presents
an inability to recognize objects despite otherwise satisfactory vision….damage to temporal lobe…can describe objects but fail to recognizenzie what they are
true or false: most brain objects activate one brain area more than another in a specialized fashion
false
what are the three objects that produces specific responses and what are the locations
- pictures of places: parahippocampal cortex
- faces: fusiform gyrus in inferior temporal cortex especially in right side
- bodies: an area close to the face area
how far one sees is dependant on what
how far light travels before it strikes ones eyes
explain sensation vs perception
sensation is registration by the sensory organ (eyes) of a physical stimuli and perception is how we interpret what we see
describe the cornea
clear outer covering, protects the eye, damage leads to eye pain and blurry vision
what is the iris
colored area, opens and closes to allow less or light through the pupil
the _______ is at the back of the eye, is the most important and has photo receptors
retina
what are the two common refractive errors? describe them
usually, normal vision focuses directly on retina….
there is myopia (near sightedness : near to you is clear) where focal point light focuses in front of/ before the retina. the eyeball is elongated or curved on cornea
hyperopia: farsightedness: focal point falls behind the retina
lens can be too flat
what is ther energy released by rods and cones when struck by light
proteins called oxins
the perception of color depends on _____
wavelength of light
what do night vision goggles use
infrared
which color cones we have the least of
blue
according to trichromatic theory what determines color
the ratio of activity across the three cones
according to opponent process theory the brain perceives color on a continuum from ____ to____ and another ______ to _____
red to green, yellow to blue
how does the inability to distinguosh between red and green occur
long and medium wavelength cones having the same photopigment
which cells make inhibitory contact onto bipolar cells
horitzontal cells
what happens when youre startled
information goes to the superior colliculis so that it can get there fast and not need higher response
axons from the ____ (____) half of each retina cross over to the oppisite side of the brain. axons from the ______ (____) half of each retina remain on the same side of the brain
nasal (inside)……. temporal (outer)
describe the optic chiasm
the junction of the 2 optic nerves from each eye
most axons go to the ____
lateral geniculate nucleus of the thalamus
what are receptive fields
part of the visual field that either excite or inhibits a cell in the visual system of the brain
what kind of receptive field do ganglion cells have
centre-surround
what are the three categories of genglion cells
parvocellular, magnocellular, koniocellular
describe parvocellular cells
theyre in the fovea, small cell body, color
describe magnocellular cells
large cell body, light and movement
what is the inability to recognize faces called
prosopagnosia
what about infants suggsest built in recogotion of faces
they look at them more than anything else
the “________ responds to a stimulis moving in a particular direction
middle temporal cortex (mt/v5)
the _______ respons to expansion, contraction or rotation of a visual stimulis
medial superior temporral cortex
