vision Flashcards
receptive fields: explain the purpose of receptive fields
2 features of central (foveal) vision
detail day vision, colour vision
what is responsible for central vision
fovea, as highest concentration of core photoreceptors
what is central vision used for
reading, facial recognition etc.
how is central vision assessed
visual acuity assessment
what does loss of foveal vision result in
poor visual acuity
3 features of peripheral vision
shape, movement, night vision
what is peripheral vision used for
navigation vision
how is peripheral vision assessed
visual field assessment
effects of extensive visual field loss
unable to navigate in environment, so may need white stick even with perfect visual acuity
what is the receptive field of a neurone
retinal space within which incoming light can alter pattern of a neurone (positive signal from stimulated photoreceptor, and negative signals from all others, to single ganglion cell)
what is the receptive field of a photoreceptor
small circular space surrounding photoreceptor
what is convergence
where retinal ganglion cells receive input from neighbouring photoreceptors
diagram of receptive field
slide 3
define convergence
number of lower order neurones field synapsing on same higher order neurone
cone vs rod system convergence
cone > rod
central vs peripheral retina convergence
central > peripheral
low convergence: receptive field, visual acuity, light sensitivity
small receptive field, fine visual acuity, low light sensitivity
high convergence: receptive field, visual acuity, light sensitivity
large receptive field, coarse visual acuity, high light sensitivity
2 types of ganglion cells
on-centre, off-centre
what are on-centre ganglion cells stimulated by (and off-centre ganglion cells inhibited by)
light at centre of receptive field
what are on-centre ganglion cells inhibited by (and off-centre ganglion cells stimulated by)
light on edge of receptive field
what are on-centre and off-centre ganglion cells important for
contrast sensitivity, enhanced edge detection
where is lowest convergence
fovea as 1:1:1 (1 cone, 1 bipolar cell, 1 retinal ganglion cell)
