M & P Pathways Different type of ganglion cells further sub divided in M and P ganglion cell: - Vary in appearance, connectivity, electrophysical properties Separate stream of information dealing with different aspects of vision (ex. Sensitivity, detail, color, motion) M: Magno (big): -Few of them (take a lot of space), large receptive field -Achromatic, insensitive to color, tells amount of light (shade of gray) perceives -Sensitive to moving stimuli, response fast to change in movement because of transient firing -Because they are large they have low acuity -Past signals to brain quickly -Habituation quickly to changes in stimuli -Insensitive to colors because getting input from cones (because we still of cones in the periphery), not disting between different type of cones and rods, the overall signals it gets can’t distinguish between wavelength P: Pavo (small): -Makes 90% of ganglion cell population -Small receptive field -Sensitive to color -Useful for detail, higher acuity -Conduct slower -Keeps responding until stimuli stops (opposite of M cell) NonM-nonP K cells (5% present) Color perception P cell: Tells difference in wavelengths Red-green cells: want to see red in center and not green in the surround Green-red cells: Wants to see green in the middle and not red in the surround Blue-yellow cells: Wants to see Blue in the center and surrounded with combination of Red and green in the surround which makes yellow Effect explains color-afterimage: causing one type of cone to over response, and in the absence of a color while reappear if staring at something else because the opposite color will over compensate (ex. Green for red) Visual parallel processing: Pathways leaving the retina are carrying different type of information Color blindness: doesn’t mean absence of color. VISION III Visual field: the space we can see when looking straight ahead. Full visual field divided in the middle. Both eyes see each others field in part. Left visual field is control by right visual cortex and vice versa. Images from one side has to cross over (optic chiasm). Decussation at chiasm. What leaves the eye is the optic nerve which turns into optic tracts. Opti tract: Temporal stays on the original side, but nasal nerves switches at chiasm. Retina to brain: damage to any of steps from retina to visual cortex will bring a certain amount of blindness. LGN: 6 layers (stacked like pancake which are slightly bend) Have layers for M type and P type and nonM-nonP type - LGN kept separate but we reorganize them from the nasal and temporal fibers First two layer receive input from M type of RGCs (deal with motion, rapid responding) Layer 3,4,5,6 are getting input from P-type RGCs (deals with color, acuity, shape) Koniocellular (non-M non P) tiny cells, in between all the other 6 layers Looking at same thing but bringing different information (M vs P type VS k type) Receptive fields: Concentric circles, (Response depends on whether or not a stimuli is in the receptive field of the particular cell that is being looked at, for example M cells???) Monocular: Only one eye activates the firing Visual cortex - V1 extends into medial portion (opening in the back of brain), touching other part but not communicating - - - - - Cells that are close to each other in the retina are looking at similar part of visual field compared to those apart. Want cell looking at the same thing to be close so they can excite each other (retinotopic maps) Retinal map is distorted Cortical magnification: how many cell are devoted to a certain area Retinotopic maps, cells near by in retina are looking at nearby in LGN in visual cortex. Cell looking at same thing be next to each other However the map is distorted. Undergoing process of Cortical magnification. Cortical magnification: Brain making sense of patent of activity and making sense of that Ocular dominance columns Use of reactive tracer in one eye, meaning all ganglionic cell will pass it to their connections, so it will spread to the LGN and visual cortex. They saw layers were radioactive and some not. Ocular dominance columns: Inputs Laye IV are monocular; one cell response to(………) Binocular: Cells get input from both eyes Many neurons in V1 respond best to bars of light. Orientation of bar of light will affect the amount of firing Orientation selectivity When looking at block of visual cortex, as move through columns of left and right eye, cells responds to different light orientation A particular cell that get ESPS firing from a group of cells that firing in concentric receptive field, will prefer the line of light that would be equivalent to all of their firing??? It not just orientation selective but some neurons are direction selective (bar of light moving in a particular direction) Moving light in one direction increase firing and in the opposite would decrease firing Simple cells: Orientation selective cells Complex cells: On and off are not obvious because the direction it is moving determine the firing rate (mostly binocular) Suggest parallel processing, M-cell responsible for direction, P-cell responsible for shape, and nonM-nonP (koniocellular) responsible for color. When we put them together we get the picture we are looking at Cortical module - Processing all necessary information (………..) Beyond V1 - Areas part of visual cortex but not Striate Dorsal Stream and Ventral stream Dorsal stream: Mt directional-selective, respond to motion more than shape, fire for optical illusion. MST responsible for navigation Ventral stream: V4 plays a role in shape and color perception. Area IT receptive field varies, important for processing faces FFA contains face specific neuron, respond to when we see a face in general, what may look like a face. Highlight prosopagnosia face blindness, can’t recognize a face from the next. Questions remain: grandmother cell how do we recognize specific individual,
