Outline 6 - 1 Outline 6: Sensory Systems, Part 1, Vision...

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Unformatted text preview: 1 Outline 6: Sensory Systems, Part 1, Vision Basic Concepts 1. Transduction - the conversion of one form of energy to another To "sense", we must be capable of converting stimuli in the environment into neural activity 2. Law of Specific Nerve Energies, Mller, 1838 The activity of a particular nerve always conveys the same kind of information to the brain. e.g., an individual neuron does not have the option of sending "rose odor" at one time and "bright red" at another time. Our perception is essentially an end result of which sensory nerves are activated by peripheral nerve receptors. Details of the perception are supplied by the pattern, timing and strength of the activation. This is true for each of the senses. If we could keep all of a retinal ganglion cell's output intact but have it receive activating input from a hair cell of the auditory system, we would "see" sounds. Similarly, connecting the auditory nerve to photoreceptors would cause us to "hear" lights and moving objects. 3. Convergence & Divergence Convergence- the axons from many neurons can converge onto a single neuron Divergence - the axon from a single neuron can provide synaptic input onto many neurons The Visual System I. Overview of the Visual Circuit The Major pathway: Retina-> Thalamus (lateral geniculate nucleus, LGN) -> Occipital cortex, aka Visual Cortex, aka Striate Cortex 2 II. Close up on the retina Rods & Cones -> Bipolar Cells -> Ganglion cells | | horizontal cells amacrine cells A. Receptor Cells: 1. Rods-more sensitive to dim light (scotopic vision ) - about 120 million in a human retina 2. Cones- more sensitive to color ( photopic vision ) - about 6 million in a human retina 3 types of cones: Cones sensitive to long (red-yellow), medium (green and less to yellow) or short (blue) wavelengths 3 Visual transduction the conversion of light to neural signals photopigments in rods and cones are transformed by light which causes a G- protein mediated decrease in sodium (Na+) permeability. Trichromatic theory- all of our color perception is based on the selective sensitivity of cones to one of three wavelengths. Rods and cones form synapses with bipolar cells: B. Bipolar cells (1) Some receive input from many rods (hundreds) - The converging input of many rods makes it more likely for a connected ganglion cell to fire in dim light than a ganglion cell that is excited by only a few inputs from cones. -The converging rod input makes the perception of details of the input less precise in comparison to the cone input (2) Some receive input from 2 to 3 of the cone varieties Typically excited by one type and inhibited by another e.g., excited by blue light via blue cones but inhibited by yellow light via red-yellow and green-yellow cones Opponent Process theory- we perceive color in terms of paired opposites - white vs black, green versus red, blue vs yellow Demonstration of opponent processes - negative afterimages 3 Visual transduction the conversion of light to neural signals...
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This note was uploaded on 04/20/2008 for the course PSY 308 taught by Professor Jones during the Spring '08 term at University of Texas at Austin.

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Outline 6 - 1 Outline 6: Sensory Systems, Part 1, Vision...

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