L3 Flashcards
how does the visual world map onto the retina
it is inversely projected onto the retina
where do 90% of the fibers in the optic nerve terminate
the lateral geniculate nucleus of the thalamus
what allows for mapping of the visual field
the response of cells in the LGN (on and off centre surround)
what is on centre
when light of the correct orientation falls onto the centra it will increase the cells firing rate and when it falls on the surround it will decrease the firing rate
this is the opposite for off centre
what is retinotopic organisation
the visual world is mapped onto the retina > LGN relationships are maintained in the nervous system
what is the patteren for LGN retinotopic mapping
how will the cells be active hen something moves across the visual field
when an object moves across the visual field the cells that respond are usually in a linear pattern
where do fibers from the LGN project to
V1 / striated cortex / brodmann’s area 17 / primary visual cortex
where is V1 located
at the very back of the occipital lobe. you cant see most of it as it is on the inside of the brain
what cells are found in V1
simple and complex cells
what is a simple cell
these respond to elongated bars or edges of light
these are orientation selective and have separate on and off subregions
these cells can be binocular or monocular
what are complex cells
these are orientation selective
have spatially homogenous receptive feild therefore they have no sporate on/off sub regions
nearly all of these cells are binocular
list the order of cells information passes through in the brain
retinal ganglion cell –> LGN –> simple cell –> complex cell
what is meant by the columnar architecture of V1
the cortex has many layers. if you look at cells at right angles to the surface to see what they respond to, they all have a receptive field which overlaps and they all have the same orintation selectivity (they all involved in processing the same part of the visual field)
when you look at cells in the horizontal plane they shift systematically and as the position of the receptors fields and preferred orintation slowly change. this shows that the cells respond to slightly different things indicating that they are responsible for a different parts of the visual world
what does retinotopy mean
remapping of the retinal image onto the cortical surface
which region of the retina has a greater magnification factor (used more of V1)
the foveal region
a local group of neurons in V1 represents what
a point in the visual field
what is an example of topographic organisation
retinotopic mapping
what is topographic organisation
an ordered representation of the sensory environment where spatially adjacent surfaces are represented in adjacent positions in the brain
what are the 2 reasons why retinotopic mapping is the most efficient way for us to perceive vision
space saving and local processing
what takes up the most space in the brain
brain volume is largely driven by axon volume because myelination takes up a lot of space
therefore reducing axon length provides space form more neurons and conserves metabolic resources
what is the most efficient way to keep axon length short in the brain
axon length is shortest when neurons that share dence connectivity are clustered together
eg like having all the cells for processing the visual field in V1
how does retinotopic mapping allow for local processing
cells are all clustered together in V1. the proximity facilitates processing such as lateral inhibition
what are sound waves
pressure pulses that travel at 340 m/s
what is the human range of hearing
20 - 20,000 Hz
describe age related hearing loss in men and women
it is much worse in men than it is for women
a 10 dB decrease in hearing does what to the perceived loudness
1/2’s it
name the structures of the outer ear
ear canal
name the structures of the middle ear
meleous, incus and stapies
name the structures of the inner ear
eustachian tube, coclia, semicircular canals
what are the nerves of the ear
vestibular nerve, facial nerve, auditory nerve
explain the effect of the sound wave in the cochlea
the coclia is fluid filled. vibrations produce waves which bend the outer hair cells which amplify the weak mechanical signal
then the inner hair cells transduce that information. they do this because the vibrations cause them to bend which open ion channels which causes an electrical signal
how is the cochlea tonotopically mapped
the base is for high frequency’s and the apex is for low
what is the pathway of sound information
cochlea –> brainstem –> midbrain –>medial geniculate nucleus of the thalamus (forbrain) –> auditory cortex
what happens at the inferior colliculus
this is where sounds that your body is producing is subtracted from your auditory signal
eg this is why you may not notice that you are chewing loud
what is the medial geniculate nucleus
this is where attention is controlled
eg if a sound comes from one side, this is the location that makes you turn to that side
describe topographic representation in the primary auditory cortex
anterior is for low frequencys and posterior is for high
why is it important that the auditory cortex is topographically mapped (5 points)
it reduces axon length because sounds that are close in frequencys and processed together
facilitates processing (lateral inhibition)
allows sound to be encoded on the basis of time/frequency changes
scene analysis allows you to detect different frequency’s in the environment (low = footsteps, high = birds)
detection of beat for social cohesion (eg the base in music makes you dance which forms social bonds)
what is top down processing
using information from a higher level mental process and prior experience
what is bottom up processing
processing that begins with the sense receptors
what % of inputs to the visual cortex are top down
6%
is the primary auditory cortex larger in old world monkeys or humans
old world monkeys (macaques)
however in humans the surrounding belt and parabelt areas are about 10x larger
where does the auditory cortex get its information from
most connectivity is top down as around 66% is from other cortical areas
why does the auditory system use so much top down processing
allows for context and procedural demands to bias perception
allows for integration of multisensory input
