Chapter 4 Flashcards
visual pathway to the brain
retina (PNS) -> optic nerve (PNS) -> optic chiasm (CNS) -> lateral geniculate nucleus <-> occipital lobe
lateral geniculate nucleus (LGN)
located in the thalamus
receives info from both retina and striate cortex
holds on visual info about receptive fields
where do 90% of light information go? what about the other 10%?
90% goes to LGN
10% goes to superior colliculus
what does the superior colliculus do?
controls eye movement
what parts in the brain does the LGN receive feedback from
striate cortex (then transmits info to dorsal and ventral streams)
other names for striate cortex
V1
primary receiving area
primary visual cortex
striate cortex
where visual info from receptive fields continue to be processed
receptive fields not organized as center-surround like retina and LGN
simple cortical cells
aka feature detectors (simple, complex, and end stopped)
side-by-side receptive fields of neurons in striate cortex
simple cells
type of feature detector
firing occurs based on non-moving stimulus presented in a specific direction through a side-by-side receptive field
complex cells
type of feature detectors
firing occurs based on moving stimulus in a specific direction where neurons produce electrical signals
detect movement but NOT what it is
end stopped cells
type of feature detectors
firing occurs based on certain moving corners, angles, and length of stimulus where neurons produce electrical signals
detect movement AND what it is
selective adaptation
exposure to a certain feature for a SHORT period of time DECREASES firing in the cortical neurons for that feature
why do neurons decrease in firing for selective adaptation?
adaptation (getting used to specific feature; firing fades for a feature that is presented repeatedly for a short while)
short term effect – adaptation occurs for a few minutes but goes away
Ex: contrast threshold (difference in light intensity)
selective rearing
exposure to a certain feature for a LONG period of time INCREASES firing in the cortical neurons
why do neurons increase in firing for selective rearing?
neural plasticity/experience-dependent plasticity (neurons can be shaped to respond in a certain way)
long term effect – neurons continue to actively respond to orientation for weeks and days
spatial organization
how the environmental stimulus is processed in specific locations of the brain
spatial = location (up, down, left, right)
image of stimulus (represented spatially in the striate cortex through electrical signals)
retinotopic map
image from retina can be electronically mapped out in area V1
electronic map
a map of electrical signals going to certain locations of the brain
cortical magnification
how the small fovea accounts for a large area in the striate cortex
fovea
makes up 0.01% of retina
8-10% of electronic map in V1 comes from fovea
cortical magnification factor
the size of the magnification
can be asses through brain imaging
cortical magnification on visual cortex based on fMRI scans
image located in fovea stimulates a larger area of the visual cortex
image located in the peripheral retina stimulates a smaller area of the visual cortex
columns
group of neurons firing in a specific area of the striate cortex
location columns
receptive fields in retina are in the same location of the striate cortex
orientation columns
neural firing in a column of the cortex occurs when stimulus is positioned in a particular direction
hypercolumns
location column w/ all orientations of a stimulus
cortical property of an image (how are images perceived in the visual cortex?)
image of stimulus does not have to look the same way in the visual cortex
neurons in visual cortex just need electrical info to represent stimulus
tiling
in relation to cortical property
location columns working together to cover entire receptive fields
streams
pathways leading to other brain areas
ablation
destruction or removal of tissue in the nervous system
goal is to understand the function of a particular area of the brain
object discrimination problem
“what” pathway – ventral stream
temporal lobe is destroyed = cannot identify objects
landmark discrimination problem
“where” pathway – dorsal stream
parietal lobe is destroyed = cannot identify locations
action pathway
“how” pathway – deals w/ taking action or what you do to an object
located in dorsal stream for “where” pathway
neuropsychology
study of behavioral effects of brain damage in humans
double dissociation
one individual has one brain area damaged (function A) but not another (function B) whereas another individual has the opposite brain area (function B) damaged and not the other (function A)
Patient D.F.
a woman who had damage to ventral stream due to carbon monoxide poisoning
unable to match orientation of a card but can physically place it in the correct orientation (how pathway intact – tells us dissociation b/w what and where pathways)
Pt with damage to parietal lobe but not temporal lobe showed opposite effect
size illusion experiment
people without brain damage can show differences in their what and how pathways by detecting line differences
length estimation task (focus on ventral pathway = perception NOT accurate; falsely assume line 1 is smaller than line 2)
grasping task (focus on dorsal pathway = perception IS accurate; fingers detect line 1 as longer than line 2)
inferotemporal (IT) cortex
type of higher-level neurons
detects patterns of objects
hippocampus
type of higher-level neurons
forming and storing memories
why is the medial temporal lobe (MTL) important?
structures involved not only in perceiving objects and concepts but also involved in remembering them
