chapter 4: the visual cortex and beyond Flashcards
describe the pathway from the retina to the brain
- optic nerve
- optic chiasm
- 90% go to lateral geniculate nucleus (LGN), 10% go to superior colliculus
- cortex
what happens at the optic chiasm
anything in the right visual field (regardless of the eye), end up on the left hemisphere of the brain
vice-versa
what is the function of the LGN and where is it located
regulates neural info as it flows from retina to cortex
- receives more signals from the cortex than the retina called “feedback”
located in the thalamus
what is the function of the superior colliculus
controls eye movement
what are the other names for visual receiving area
striate cortex
V1
what are simple cortical cells
cells in the striate cortex with side-by-side receptive fields that have excitatory and inhibitory areas
Explain how simple cells respond best to certain orientation
- layout of the excitatory and inhibitory areas are parallel to each other
- the more tilted it is, the more it will stimulate the inhibitory area and decrease firing rates
what are complex cells
cells that respond best to correctly oriented bar of light that moves across the entire receptive field
what are end-stopped cells
cells that fire to moving lines of a specific length or to moving corners or angles
what are end-stopped cells
cells that fire to moving lines of a specific length or to moving corners or angles
why are simple, complex and end-stopped cells also called feature detectors
because they fire in response to specific features of the stimulus, such as orientation or direction of movement
define selective adaptation
firing causes neurons to eventually become fatigued or forces them to adapt
what are the two physiological effects caused by selective adaptation
- neuron’s firing rate decreases
- neuron fires less when that stimulus is immediately presented again
define what is the contrast threshold that was used to measure the effect of selective adaptation to orientation
minimum intensity difference between two adjacent light and dark bar until they can barely be seen
define selective rearing
if an animal is reared in an environment that contains only certain types of stimuli, then neurons that respond to these stimuli will become more prevalent
explain why results of selective rearing experiments are described as “use it or lose it”
presenting the rearing orientation over a period of days/weeks keeps the neurons that respond to that orientation active.
- other neurons lose their ability to respond to their orientations
explain the experiment done by Blakemore and Cooper on the kittens
- kittens kept in the dark from birth to 2 weeks
- then placed in striped tube for 5 hours a day
kittens seemed blind to orientation that they hadn’t seen in the tube
what is the retinotopic map
electronic map of the retina on the cortex
define the cortical magnification and cortical magnification factor
apportioning of a large area on the cortex to the small fovea
- cortical magnification factor: size of magnification
true or false? the more space on the cortex allocated for an image translates into a larger size of the image
false, it translates into a better detailed vision
explain what location columns and orientation columns are
organization of the cortex where all neurons in a perpendicular column to the surface of the cortex represent the same location on the retina and the same orientation
define a hypercolumn
a location column with all of its orientation columns
explain the tiling effect
a scene is divided into small areas. each area sends info to one location column. together, they cover the entire visual field
true or false? each visual area can overlap each other
true
explain how visual signals are processed as they move from V1 to higher-level extrastriate areas
receptive field sizes gradually increase.
as we move up this hierarchy of extrastriate cortex, visual scene builds up from line or edge to entire shapes and objects
define the technique called ablation
destruction or removal of tissue in the NS
describe the object/landmark discrimination problem and the ablation part of the experiment
object: be able to discriminate between two objects and put aside “target object”
landmark: be able to remove cover of food closest to “landmark”
ablation: temporal or parietal lobes removed
conclusion: what and where pathway
what does the term dorsal and ventral refers to
dorsal: back or upper surface of an organism
ventral: lower part of the brain
true or false? specific ganglion cells exists for both dorsal and ventral stream
true
define neuropsychology
study of the behavioral effects of brain damage in humans
what is the double dissection method
damage to one area of the brain causes function A to be absent while function B is present in one patient
damage to another area of the brain causes function B to be absent while function A is present in another patient
why can the dorsal pathway also be called the how pathway
because it determines how a person carries out an action.
explain the experiment that supports the idea that perception and action are served by different mechanisms
illusion: line 1 is longer, line 2 appears longer
- task 1: length estimation task
- task 2: grasping task
illusion works for perception not for action
describe the neurons found in the inferotemporal cortex
increase in receptive fields continues through the what stream
- largest receptive fields at the apex of the stream in IT cortex respond to more complex objects
name a few structures in the medial temporal lobe (MTL)
parahippocampal cortex
entorhinal cortex
hippocampus
the MTL structures are extremely important for __
memory
define the contextual modulation effect
effect of stimulating outside the receptive field can affect what’s happening within the receptive field
describe gross’s experiments on neurons in the IT cortex of the monkey
presented stimuli like lines, squares, circles, etc
- one neuron refused to respond to anything, until experimenter pointed at something in the room
- expanded types of stimuli presented
- found neurons that responded to real-life, complex objects like hands and faces
what is the link between MTL neurons and hippocampal neurons
neurons in the MTL that respond to perceiving specific objects or events are also involved in remembering these objects and event
what is perceptual organization
lines of the same orientation are perceived as a group that stands out from the surrounding clutter
