problem 2 - the visual brain Flashcards
the lateral geniculate nucleus (LGN)
- in the thalamus
- regulates info coming from the retina to the visual cortex
- for every 10 nerve impulses the LGN sends back 4 to the cortex
- LGN neurons have the same center-surround configuration as retinal ganglion cells = respond best to small spots of light on the retina
layers of the LGN
LGN is organized into 6 layers
* each layer receives signals from only one eye
* 1, 4 & 6 = contralateral eye
* 2, 3 & 5 = ipsilateral eye
* each eye sends half of the information to the LGN in left hemisphere and half to LGN in right
magnocellular cells (LGN)
size: large
location: layers 1 & 2
function: for dynamic visual properties like movements
parvocellular cells (LGN)
size: small
location: layers 3, 4, 5 & 6
function: for texture & color
koniocellular cells (LGN)
size: very small cell bodies
location: between each layer of M & P cells
function: for color
super colliculus
an area involved in controlling eye movements & other visual behaviors that receives about 10% of the fibers from the optic nerve
striate cortex (aka primary visual receiving area)
in the occipital lobe
3 types of cells: simple cortical, complex & end-stopped
neurons respond to some patterns of light & not to others
simple cortical cells (striate cortex)
- have excitatory & inhibitory areas
- arranged side by side
- respond best to bars of a particular orientation (specific orientation)
complex cells (striate cortex)
- respond best to movement of a correctly oriented bar across the receptive field
- respond best to a particular direction of movement
end-stopped cells (striate cortex)
- fire to moving lines of a specific length or to moving corners or angles
- respond best when the corner moves upward
orientation tuning curve
indicates the relationship between orientation and firing
determined by measuring the responses of a simple cortical cell to bars with different orientations
selective adaptation
if neurons fire for long enough, they become fatigued, or adapt - this adaptation causes 2 physiological effects:
1. The neuron’s firing rate decreases
2. The neuron fires less when stimulus is immediately presented again
Adaptation is selective because only the neurons that respond to verticals or near-verticals adapt, and other neurons do not
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
use it or lose it principle
retinotopic map
a map in which each point on the LGN corresponds to a point on the retina
occur in each of the 6 layers and the maps of each of the layers line up with one another
maps in the striate cortex
Similar to retinotopic maps: nearby points in the striate cortex receive signals from nearby locations on the retina
Cortical magnification factor: apportioning the small fovea with a large area on the cortex
location columns (striate cortex)
are perpendicular to the surface of the cortex so that all of the neurons within a location column have their receptive fields at the same location on the retina
orientation columns (striate cortex)
each column contains cells that respond best to a particular orientation
orientation of columns depends on the orientation that they respond to
ocular dominance columns (striate cortex)
neurons in the cortex are also organized with respect to the eye to which they respond best = each neuron encountered along a perpendicular electrode track responds best to the same eye
Most neurons respond better to one eye than to the other = ocular dominance
hypercolumns (striate cortex)
all 3 types of columns can be combined into this larger unit
* has many columns that all together are responsible for all functions
* is like an idea (not real)
the what pathway (vision)
ventral pathway - temporal lobe
* associated with object discrimination
the where pathway (vision)
dorsal pathway - parietal lobe
* associated with landmark discrimination
* is for taking action & knowing the location of the object (where)
* also involves physical interaction with the object (how)
single dissociation
2 groups are tested on 2 tasks and between group difference is apparent only in one task
Used to know if a certain brain area is involved in a certain function
* Group 1 would be control, group 2 would be people with brain damage for example
* Both groups do the same 2 tasks - one task they would both perform the same and in the other task the experimental group would perform worse
double dissociation
Has 3 groups
1. group impaired with area A
2. group impaired with area B
3. group with no impairements
* Performances can be compared to each other
* stronger evidence - can see exactly where the impairment comes from
solves problem w single dissociation: no longer reasonable to argue that a difference in performance results merely from the unequal sensitivity of the two tasks
achromatopsia
dont see colors
* disturbance in the CNS
* seeing in shades of gray (depth and texture remain intact)
* associated with lesions encompassing V4 and region anterior to V4 (ventral pathway)
akinetopsia
not seeing movement / loss of motion perceptin
* Seeing moving objects as snapshots → one position and suddenly another
* Lesion at V5/MT – middle temporal area
* Only when lesion is bilateral = akinetopsia, people can perceive motion as long as V5 is intact in at least one hemisphere
