precise detail) than rods; concentrated most heavily in the centre of the retina and fall off
in density toward its periphery.
-fovea: a tiny spot in the centre of the retina that contains only cones; visual acuity is
the greatest at this spot.
-rods: specialized visual receptors that play a key role in night vision and peripheral
vision; more sensitive to dim light; outnumber cones in the periphery of the retina;
density is greatest outside the fovea and gradually decreases toward the periphery of
the retina; adverted vision for dark objects.
-dark adaptation: the process in which the eyes become more sensitive to light in low
illumination; complete in 30 mins.
-light adaptation: the process whereby the eyes become less sensitive to light in high
illumination. improves visual acuity
-receptive field: made up of rods and cones in the retinal area, when stimulated, affects
the firing of the visual cell.
-lateral antagonism: occurs when neural activity in a cell opposes activity in
Vision and the brain
-optic chiasm- the point at which the optic nerves from the inside half of each eye cross
over and project to the opposite half of the brain
-axons from the left half of each retina carry signals to the left side of the brain, vice
-after meeting the optic chiasm, the optic nerve fibres diverge 2 pathways, the main
pathway projects into the thalamus (brain’s major replay station); the second visual
pathway leaving the optic chiasm branches off to superior colliculus (midbrain);
function of 2nd pathway is the coordination of visual input with other sensory input.
-90% of the axons from the retinas synapse in the lateral geniculate nucleus (LGN);
visual signals are processed in the LGN and distributed to areas in the occipital lobe that
make up the primary visual cortex.
-Main visual pathway is subdivided into: magnocellular (processes info regarding
brightness) and parvocellular (handles perception of color) channels. they engage in
parallel processing, which involves simultaneously extracting different kinds of info from
the same input.
-simple cells respond best to a line of the correct width, oriented at the correct angle,
and located in the correct position in its receptive field.
-complex cells more responsive if a line sweeps across their receptive field, only if it
moves in the right direction.
-feature detectors: neurons that respond selectively to very specific features of more
-after visual input is processed in the primary visual cortex, it travels through 2 streams:
ventral stream (processes the details of what objects are out there, perception of form
and color of the external world); dorsal stream (processes where the objects are,
perception of motion and depth; visual control of action)