visual development Flashcards
where do axons from the neurones of the retina grow?
to the thalamus, where they form synapses with neurones in the thalamus in a very organised arrangement
-> axons from the thalamus neurones grow towards the visual cortex in the occipital lobe
how do columns in the visual cortex receive stimuli
from L eye, to R eye to L to R
- > alternating pattern
- > info from the same area of the retina in the right and left rhe synapse next to each other, gives the brain the ability to create one 3D image
when are the columns in the visual cortex formed?
before the critical period for development of vision
where does eveidence.for the critical period come from?
animal models
one group of monkeys were raised in the dark for 3-6 months
another group raised in the light, with no exposure to patterns.
-> what was found?
both groups had difficulty with object discrimination and pattern recognition.
=> visual development requires light and patterns
what did hubel and wiesel do?
raised monkeys from birth to 6 months, depriving them of any light stimulus in one eye ( monocular deprivation )
=> blind in the light deprived eye when it was exposed to light
=> retinal cells did respond to light stimuli, cells of the visual cortex did not.
deprivation for only a single week during a certain period after birth produced the same result
monocular deprivation in kittens results
under 3 weeks- no effect
after 3 months - no effect
at 4 weeks - major effect, even if closed for a matter of hrs
born blind… under 3weeks= no effect
over 3 months = connections made = no effect
4weeks = critical period & lack of stimulation = development effected
what happens during the critical period?
at birth = overlap between the territories of axons
adults = less overlap
after monocular deprivation, columns with axons from the light deprived eye take up more territory in the visual cortex.
=> visual stimulation required for the refinement of columns & full development of the VC
what do axons do in the VC
compete for target cells
-> every time a neurone fires onto a target, they stnapse of another axon sharing the target cell is weakened.
-> if this happens repeatedly, the synapses that are not firing are cut back.
=> when one eye is deprived of light, tbe axons will not be stimulated, only those of the eye getting light will fire.
=> the synapses from the deprived eye will be weakened and eventually lost
what is stereoscopic vision?
close objects ( less than 30 m )
- > visual field is seen from 2 angles
- > cells in the VC let us compare images from one eye to the other
how can we see distant objects
images on the retinas look simailar
-> use visual cues and past experiences
what helps judge depth
overlaps & colour changes
what does the carpentered world hypothesis suggest?
people who live in a world dominated by straight lines and right angles perceive depth diffent to those who live in a circular culture
are depth cues innate or learned
learned
what baby behaviours must be determined by genes?
crying
walking
grasping
within 24hrs of birth, newborns can distinguish human faces and voices
