PSY 318 Wolf CH3 Visual Pathway

complex cells

Cells in V2 that give best response to moving lines of particular orientation Larger receptive fields Less sensitive to location of bar than simple cells Input from more LGN cells than simple cells get Allows larger field, more complex response

the snellen E test

Herman Snellen invented this method for designating visual acuity in 1862. The strokes on the E form a small grating pattern.

LGN 6 layers

Orders info from visual fields Left visual field: left side of body, processes in right LGN (F-A) Right visual field: right side of body, processed in left LGN (F-A) Layers 2,3,5 come from the same side Layers 1, 4, 6 come from opposite side Cells line up from middle outward half closes to nose crosses over, other half doesn't Topographic map

hypercomplex cells

in vision, cells that respond to particular orientations and particular lengths

complex cells in V1

respond to light or dark bars over a broad area

simple cells in V1

respond to lines of a certain angle (edges) Some cells prefer bars of light, some prefer bars of dark Analogous to on-center, off center Orientation turning: prefer bars in specific directions

orientation turning

tendency of neurons in striate cortex to respond more to bars of certain orientations and less to others

cortical magnification

the amount of cortical area devoted to a specific region in the visual field Devote more cortex to fovea than periphery Consequences: Lower resolution in periphery 1. Less brain area for processing 2. Visual crowding Objects in periphery blend with each other Have to move eyes to see them clearly

visual crowding

the deleterious effect of clutter on peripheral object recognition

spatial frequency

the number of cycles of a grating per unit of visual angle Number of times a pattern repeats per unit area Not as simple as fewer cycles (thicker bars) easier to see

topographical mapping

the orderly mapping of the world in the lateral geniculate nucleus and the visual cortex

phase vision

the relative position of a grating how the bars line up on the ganglia

Acuity

the smallest spatial detail that can be resolved sharpness of vision

column

vertical arrangement of neurons in striate Within a column, all neurons prefer same orientation Receptive field changes as you move down Across, column, orientations change

Hubel and Wiesel discovered the bar shaped receptive fields

How do you get from circular fields to bars? Cell in striate receives input from several LGN/retinal ganglion cells Line up circular fields to make any orientation Mostly vertical or horizontal V1 responds to lines POINTELISM/PIXELS Hubel and Wiesel discovered the bar-shaped receptive fields The experiment Simple cells Each striate cell responds strongest to specific features like: Movement Specific directions Bars Edges Gratings Specific frequency and orientation Preferences act like a filter -Each LGN cell responds to one eye or the other, never to both. -Each striate cell can respond to input from multiple LGN cells/layers -Striate cells are the first to combine info from both eyes

hyper column

In the striate cortex, unit proposed by Hubel and Wiesel that combines location, orientation, and ocular dominance columns that serve a specific area on the retina. 1-mm block of striate, many columns One receptive field Contains columns responding to every possible orientation (0-180 degrees)

Striate cortex

The visual receiving area of the cortex, located in the occipital lobe. processes visual info Also called Primary Visual Cortex (V1) (if destroyed we have no conscious vision/blind)(no dream in images)

lateral geniculate nucleus (6 layers)

a place in the thalamus that receives impulses from the optic nerve (wire from retina to middle of brain) two nuclei, a right and left (all senses except smell go thru the thalamus Layers 1-2: Magnocellular.(rods: bigger than cones) (ganglion cells) Large cells, input from M ganglion cells, Respond best to large , fast-moving objects. Layers 3-6 Parvocellular: CONES Smaller cells, input from P ganglion cells. Respond best to fine spatial details of stationary objects. (cannot respond to dim, like constant detail) Layers 1-6 are 80% of optic nerve Koniocellular: very small cells in between the magnocellular and parvocellular sections (disorganized bits in between the nice organized cells)

retinal ganglion cells

contribute to processing of stripes, lines, edges organize the signals and send them to the brain