NPB 110B - MT2 Visual Systems (receptive fields)

optic nerve

bundle of axons from retinal ganglion cells that are stuck together encoding visual scene, flows out of the eye

optic chiasm

crossing of subset of retinal ganglion axons

optic tract

rebundling of axons after they have crossed the chiasm

lateral geniculate nucleus

visual subdivision of the thalamus, where they make a synapse and then thalamic cells project to the cortex

primary visual cortex (V1)

anatomical target of thalamic input

Lateral visual pathway

carries action potentials from retinal ganglion cells in temporal retina and conveys info to contralateral visual field

Medial visual pathway

carries action potentials from retinal ganglion cells in nasal retinal, conveys info from ipsilateral visual field

where is the left part of the visual fields encoded

right half of nasal half of the left eye and right half of temporal half of the right eye

what happens at optic chiasm

axons in medial portion of each optic nerve crosses to the opposite side

right optic nerve

contains all info for right eye

midline/medial axons

show info for left side of left eye and right right side of right eye

optic tract

contains info for both eyes about contralateral fields

major cellular layers

magnocellular (lower 2 layers), parvocellular (upper 4 layers)

magnocellular

larger receptive fields, better sensitivity, motion processing (course details)

parvocellular

smaller receptive fields, better acuity, color processing (fine details)

primary visual cortex

representation of visual field, divided into 12 sections

disproportionate representation

more cortical representation devoted to the fovea, topographic map

simple cell in V1

cell that responds primarily to oriented edges and gratings, have elongated subregions that respond either to light or dark

simple cells receptive field

built by convergent input of more than 1 LGN cell

good stimulus for simple cells

vertically oriented bar of light covering excitatory field centers of each input cells

orientation tuning

action potential spikes are used to create a tuning curve, arranged in columns

orientation columns

V1 is organized into narrow columns of cells, like somatosensory cortex

major pathways of visual system

dorsal and ventral

dorsal pathway

“where” (location and action), middle temporal visual area

ventral pathway

“what” (object recognition, inferotemporal cortex

inferotemporal cortex

higher order part of cortex, has part that is responsible for recognizing faces in monkeys and people, likes all features organized in specific way

prosopagnosia

failure to identify faces