Cognitive Neuroscience of Language October 8, 2004 Lecturer: Marielle Lange Today’s goals Cognitive Neuroscience of Language Look at the pathways that conduct the visual information from the eye to the visual cortex 5 From eye to brain Marielle Lange http://homepages.inf.ed.ac.uk/mlange/teaching/CNL/ Today’s reading Leff, A.P., Crewes, G.T., Scott, S.K., Kennard, C., Wise, The Eye R.J.S. (2001). The functional anatomy of single-word reading in patients with hemianopic and pure alexia. Brain, 124, 510-521 Available at the ITO. Visual Perception of Print. Source to identify. 1
Cognitive Neuroscience of Language October 8, 2004 Lecturer: Marielle Lange Light: The physical stimulus Structures of the Human Eye Light is a form of radiant energy. This energy is radiated in waves that have a characteristic wavelength. http://www.nipissingu.ca/stange/courses/P1106/SANTROCKPP/Chapter05.ppt Psychology: Second Canadian Edition by Santrock and Mitterer. Retina, as seen through pupil The retina is a tissue that is an extension of Photoreceptors the brain. On-line book, Anatomy and Physiology, Martini. http://media.pearsoncmg.com/ph/esm/esm_martini_fundanaphy_5/bb/obj/14/CH14/html/ch14_4_1.html 2
Cognitive Neuroscience of Language October 8, 2004 Lecturer: Marielle Lange Structure of the retina Characteristics of Rods and Cones Three types of cones (reacting to blue, red, green ranges of wavelength). Their stimulation in various combinations 120 million per eye 8 million per eye provides the perception of different colours. http://www.nipissingu.ca/stange/courses/P1106/SANTROCKPP/Chapter0 http://www.arts.uwaterloo.ca/~cellard/teaching/PSYC261/vision/vision.ppt 5.ppt Psychology: Second Canadian Edition by Santrock and Mitterer. Distribution of rods and cones Ganglion cells on/off surround http://www.physiology.wisc.edu/neuro524/vision.htm 3
Cognitive Neuroscience of Language October 8, 2004 Lecturer: Marielle Lange Centre-surround Ganglion Cell, receptive fields antagonism In the visual pathway, the message must cross two synapses before it heads toward the brain. On-center ganglion cells: excited when light falls In other sensory pathways at most in the center of their one synapse lies between a receptor receptive field. Inhibited and a sensory neuron. when light falls on the The extra synapse adds to the surround. synaptic delay, but it provides an opportunity for the processing and (Only a weak response is integration of visual information evoked by a uniform field of before it leaves the retina. light. ) On-line book, Anatomy and Physiology, Martini. http://www.arts.uwaterloo.ca/~cellard/teachi http://media.pearsoncmg.com/ph/esm/esm_marti ni_fundanaphy_5/bb/obj/14/CH14/html/ch14_4_1 ng/PSYC261/vision/vision.ppt .html Retinal Output Hubel & Wiesel (Ganglion) Cells 10% are magnocells (large) : fast responses - for timing visual events, visual motion, controlling eye movements, coarse features (low ‘spatial frequencies’), high contrast sensitivity 80% are parvocells (small) : for colour, high acuity, fine detail (high spatial frequencies), low contrast sensitivity Visual magnocellular pathways control eye movements, and are particularly important for maintaining steady fixation 4
Cognitive Neuroscience of Language October 8, 2004 Lecturer: Marielle Lange Optic disc & start of optic nerve Optic disk, optic nerve, optic chiasm, optic tract Optic nerves, Optic chiasm, optic tract Lateral Geniculate Nucleus (LGN) http://www.neuromod.org/ courses/np2000/disorders- attention-awareness- Lateral (pupillary reflex, Geniculate kok/disorders-attention- orient eyes towards Nucleus awareness-kok.ppt objects) (LGN) 5
Cognitive Neuroscience of Language October 8, 2004 Lecturer: Marielle Lange Lateral geniculate nucleus Axonal pathway to the LGN (LGN) The Lateral Geniculate Nucleus Left eye Right eye (LGN) deals with visual information, sending some to reflex centers in the brain stem, other to The LGN has the the visual cortex. six layers each of which gets Functions: Enhance independent information about input from contrast, organizes either the left or information, receives the right eye feedback from other but not both. areas. The Thalamus is mostly a relay center. http://www.neuromod.org/courses/ecba1999/perce http://www.physiology.wisc.edu/neuro524/vision.htm ption-and-attention/perception-and-attention.ppt Magnocellular and parvocellular projections The magno cells (large) are part of the m-pathway -- primarily responsible for processing information about motion and flicker . The parvo cells (small) are part of the p-pathway -- primarily responsible for processing information about form, Large ganglion cells Small ganglion cells colour, and texture . Colour sensitive Colour in sensitive In fovea, Large Receptive Fields monitor cones, Small Receptive Fields Low resolution with 1:1 High resolution` Can receive info from as connections Slow, sustained resp. Fast, transient response. many as 1000 rods - More sensitive at low More sensitive at high coarse coding contrast contrast 6
Cognitive Neuroscience of Language October 8, 2004 Lecturer: Marielle Lange Striate cortex (V1, Area 17) Visual Cortex (or striate cortex) Primary and association areas http://www.physiology.wisc.edu/neuro524/vision.htm Retina, geniculate-striate system 1,000,000 axons! Axons carrying Retinotopic maps signals from neighbouring parts of the retina are next to one another within the optic nerve. http://www.driesen.com/retino-geniculate- striate_system.htm 7
Cognitive Neuroscience of Language October 8, 2004 Lecturer: Marielle Lange What Do Images Look Like V1: Topographic in Cortex? representation Bottom image: Slice through area V1. The cells that have stained dark are those that Original image were responding while the animal viewed the stimulus shown above. Preservation of spatial structure topographic representation. “Retinal” image Important because of the vast numbers of cells (~100,000,000 in each hemisphere's V1). Note also how the cortex expands the “Cortical” image representation of the fovea relative to the periphery (cortical magnification). LGN to V1 connections Cortical organization Information travels from the LGN primarily to layer 4 of V1 but not all of in V1: the information goes to the same part of layer 4. Magnocellular layers of the LGN project to an upper subdivision of layer 4 in V1 Layered and Columnar and the he parvocellular layers of the LGN to a lower subdivision of this layer. Organization Separation of information (e.g., motion vs. colour) so that it can be processed separately. 8
Cognitive Neuroscience of Language October 8, 2004 Lecturer: Marielle Lange Columnar Columnar organization organization 1: few cells (‘molecular’ layer) Each column can The surface of the cortex be seen as a 2: -> V2 is divided into functionally computational distinct regions or unit that codes a microcolumns, each specific about 30 µ m in diameter. information (orientation, direction, colour). Neurons within a column will tend to increase or Here: orientation 5: motor cortext, decrease their firing rates 6: feedback cx columns together. (Pinwheel demo on course’s website) http://www.physiology.wisc.edu/neuro524/vision.htm Hubel and Wiesel’s Selectivity hierarchical model of visual cortical processing Cells in V1 do not stick to the same sort of circular, center/surround organization as the ganglion cells Simple cells respond to lines in a particular They have more complex organizations that allow for new orientation sorts of selectivity that does not occur before we reach the visual cortex. Complex cells respond to lines in a particular orientation, which move in a certain direction http://www.arts.uwaterloo.ca/~cellard/teaching/PSYC261/ vision/vision.ppt 9
Cognitive Neuroscience of Language October 8, 2004 Lecturer: Marielle Lange Orientation selectivity in V1 V1: Position selectivity Orientation selectivity Position selectivity in simple cells in V1. This cell responds The figure shows receptive field maps best when the stimulus of the for several different sorts of simple cells. appropriate orientation and size is in one particular The + symbols show positions where position. the cell responds well to a light spot, and the - symbols show positions where the cells responds well to a dark spot. V1: Direction selectivity V1: Colour selectivity This cell responds best when a blue This cell responds best when bar of the appropriate orientation, the stimulus moves up and to size, and position is presented on a the left. yellow background. This response is not based on Note that this cell is not responding to solely the orientation of the just the combination of blue and moving bar, because when the yellow, because when we reverse the same bar moves in the colours of the bar and the opposite direction, the cell background, the cell's response is responds at a significantly reduced significantly. reduced level. 10
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