chapter 4 part 1 Flashcards
area v1
visual receiving area of the brain, called v1 because it is the first visual area in the cortex - also called the striate cortex
complex cells
neurons in the visual cortex that respond best to moving bars with particular orientations
contextual modulation
change in response to a stimulus presented within a neuron’s receptive field caused by stimulation outside of the receptive field
contrast threshold
intensity difference between two areas that can just barely be seen - often measured using gratings with alternating light and dark bars - changing intensity difference until the bars can just barely be seen
optic chiasm
meeting point of the optic nerves from each eye - some cross over to the opposite side - means that all fibres corresponding to one visual field (left or right) end up on the contralateral side to that field, regardless of which eye they come from
where do visual signals go from the optic chiasm?
about 90% go to the lateral geniculate nucleus in the thalamus of each hemisphere while the other 10 percent goes to the superior colliculus, which controls eye movements
function of lgn
- neurons have centre surround receptive fields
- regulates neural information as it flows from the retina to the cortex
- receives information from the brain (actually receives more signals from the cortex than from the retina), which helps regulate which incoming information goes to the brain
occipital lobe
receives info from the lgn and acts as the visual receiving area - also called the striate cortex or v1
simple cortical cells
cells in the striate cortex that have excitatory and inhbitory areas like centre surround fields in the retina and lgn
the difference is that the fields are organized side by side rather than in centre surround - respond best to vertical bars of light, lines or edges of particular orientations depending on the cells
orientation tuning curve
the relationship between orientation of a line and firing in a v1 neuron - found by measuring the responses of a simple cortical cell to bars with different orientations
complex cells
cortical neruons that respond to moving lines - barlike stimuli- these cells only respond when a correctly oriented bar of light moves across the entire receptive field - some cells respond best to a particular direction of movement
end stopped cells
cell in the visual cortex that fires to moving lines of a specific length or to moving corners or angles- ex a neuron that fires to a medium sized corner moving upwards
feature detectors
simple complex and end stopped cells - all fire in response to certain features of stimuli - as we travel farther from the retina, feature detectors become more and more complex
lateral geniculate cells
centre surround receptive fields very similar to the receptive field of a ganglion
selective adaptation
a procedure used to measure the physiology behaviour relationship between neurons in the cortex and perception
- based on the idea that firing eventually causes neurons to become fatigued, or to adapt - neurons will decrease their firing rate and fire less when that stimulus is immediately presented again
adaptation is selective because only the neurons that were responding to the stimuli adapt, and the ones that were not responding do not
supports the idea that feature detectors play a role in perception - decreasing sensitivity can be interpreted as a perceptual result
selective adaptation procedure
- measure a persons contrast threshold
- adapt them to an orientation by having them view a high contrast adapting stimulus
-remeasure the contrast threshold of all the test stimuli
theory is that adaptation should cause an increase in the contrast threshold, making it harder to see low contrast stimuli
selective rearing
idea that 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
based on the fact that adaptation is a short term effect - selective rearing is longer term -‘use it or lose it’
neural plasticity/experience dependent plasticity
the idea behind selective rearing: response properties of neurons can be shaped by perceptual experience
selective rearing in kittens
kittens who were forced to live in a plexiglass tube with no corners or edges other than the stripes on the tube and who were unable to move their heads to see see oblique or horizontal stripes (cone) were blind to orientations they had not been exposed to - neurons didn’t respond to horizontal stimuli
retinotopic map
stimulation of different areas on the retina activate corresponding areas of the cortex
the map of the retina on the cortex is called a retinotopic map - this means that two points that are close together on an object and on the retina will activate neurons that are close together in the brain
cortical magnification
spatial representation on the cortex is distorted - more space is allotted to locations near the fovea than to locations in the peripheral retina
the fovea accounts for 8 to 10 % of the retinotopic map, while it accounts for only 0.01 percent of the retina’s area
cortical magnification factor
the size of cortical magnification - space for the fovea on the cortex
information about what we are looking at directly takes up more space on the cortex than what is off to the side
