Vision Lecture Notes PDF

Vision X.Liu PSYC 5130 EXAM 1 7:45 PM Sharp, 26 Feb 2024 Review Session: 6:30 PM X.Liu PSYC 5130 Receptor—Photoreceptors in Retina X.Liu PSYC 5130 The Eye (a) The anatomy of the eye. (b) The extraocular muscles move the eye. X.Liu PSYC 5130 Layers of the Retina The human retina contains layers of ga...

Vision X.Liu PSYC 5130 EXAM 1 7:45 PM Sharp, 26 Feb 2024 Review Session: 6:30 PM X.Liu PSYC 5130 Receptor—Photoreceptors in Retina X.Liu PSYC 5130 The Eye (a) The anatomy of the eye. (b) The extraocular muscles move the eye. X.Liu PSYC 5130 Layers of the Retina The human retina contains layers of ganglion, bipolar, and photoreceptor cells. X.Liu PSYC 5130 Differences Between Rod and Cone More Rods than Cones Rods: 120 million/eye Cones: 6 million/eye Location X.Liu PSYC 5130 Fovea is a thinning (“pit”) of the retina at the center Lateral displacement of ganglion cells from fovea Allows light to strike the photoreceptors w/o passing through other retinal layers No rods, only cones X.Liu PSYC 5130 X.Liu PSYC 5130 Transduction Process by which energy from the environment is converted to a change in membrane potential in a neuron Converts external stimulus to internal stimulus First step in visual perception X.Liu PSYC 5130 Transduction Recall the resting potential in most neurons is at ____ mv? In complete darkness, the resting potential of photoreceptors is -40 mv Less negative intracellularly than is typical The depolarization is caused by the constant influx of Na+ ions through special channels in the photoreceptors, known as the DARK CURRENT There is a messenger produced intracellularly that opens the Na+ gates X.Liu PSYC 5130 Transduction Photoreceptors HYPERPOLARIZE in response to light Initiated by the absorption of light by a photopigment in the membrane of the photoreceptors called RHODOPSIN (in rods) and Cone-Opsin (in cones). The effect of light on -opsin serves to activate an enzyme that breaks down the messenger responsible for opening the Na+ channels Channels close, membrane hyperpolarizes X.Liu PSYC 5130 Neural Circuitry in the Retina Light striking a photoreceptor produces hyperpolarization, so the photoreceptor releases less neurotransmitter. Because the neurotransmitter normally hyperpolarizes the membrane of the bipolar cell, the reduction causes a depolarization. This depolarization causes the bipolar cell to release more neurotransmitters, which excites the ganglion cell. X.Liu PSYC 5130 Differences Between Rod and Cone Rods work under low-intensity light – high sensitivity, low acuity Cones responsible for acuity, require more light X.Liu PSYC 5130 Foveal vs. Peripheral Acuity Ganglion cells in the fovea receive input from a smaller number of photoreceptors than those in the periphery and provide more acute visual information. X.Liu PSYC 5130 Receptive Field Neurons exhibit selectivity in the stimuli to which they respond e.g., a neuron might be excited by particular properties of light, sound, etc. The location of the receptive field of a particular neuron depends on the location of photoreceptors that provide it with visual information X.Liu PSYC 5130 X.Liu PSYC 5130 Differences Between Rod and Cone Three types of cones (three types of cone-opsins), but one type of rod (rhodopsin) X.Liu PSYC 5130 Perceiving Color Trichromatic Theory Mixing the three receptor types (Blue, Green, Red) via their relative activity gives us color… Color Blindness Genetic defects in color vision result from anomalies in one or more of the three types of cone Protanopia (lacking red cone) Deuteranopia (lacking green cone) Tritanopia (lacking blue cone) Monochromatic vision X.Liu PSYC 5130 X.Liu PSYC 5130 Perceiving Color The trichromacy theory accounts for much data, but incomplete e.g., red-ish yellow, green-ish blue red-ish green? yellow-ish blue? X.Liu PSYC 5130 A Negative Afterimage Stare at left for 30 seconds, then shift to right X.Liu PSYC 5130 Opponent Process Theory Receptive Fields of Color-Sensitive Ganglion Cells (60% or ganglion cells) When a portion of the receptive field is illuminated with the color shown, the cell’s rate of firing increases. When a portion is illuminated with the complementary color, the cell’s rate of firing decreases. X.Liu PSYC 5130 Opponent Process Theory X.Liu PSYC 5130 Opponent Process Theory Afterimage: When ganglion cells are excited or inhibited for a prolonged period of time, they later show a rebound effect, firing slower or faster than normal. X.Liu PSYC 5130 Perceiving Shape and Object Ganglion cells are sensitive to edge Mach bands X.Liu PSYC 5130 Three Types of Ganglion Cells ON cells are excited by light falling in the central field (center) and inhibited by light falling in the surrounding field (surround) OFF cells are excited by light falling in the surround and inhibited by light falling in the center ON/OFF ganglion cells are briefly excited when light is turned on or off – detect moving or suddenly appearing stimuli X.Liu PSYC 5130 ON and OFF Ganglion Cells This figure shows responses of ON and OFF ganglion cells to stimuli presented in the center or the surround of the receptive field. X.Liu PSYC 5130 ON and OFF Ganglion Cells https://isle.hanover.edu/Ch03Eye/Ch03CntrSurCo ntrast_evt.html X.Liu PSYC 5130 As a Consequence Information in the world is not given equal weight. Areas where luminance changes sharply (edges) are given emphasis. This is another example of the perceptual system “creating” the world. X.Liu PSYC 5130 Key Elements X.Liu PSYC 5130 Key Elements X.Liu PSYC 5130 Primary Visual Pathway X.Liu PSYC 5130 The Visual Pathway X.Liu PSYC 5130 Visual Pathway The Optic Nerves located at back of eye; bundled axons of ganglion cells Join together and cross at base of brain to form optic chiasm Convey information to dorsal lateral geniculate nucleus (LGN) (First Synapse) Information projects back to Primary Visual Cortex Projects to Higher Visual Cortical Regions (Extrastriate Cortex) V1 = Striate Cortex = Primary Visual Cortex V2-V5 = Extrastriate Cortex X.Liu PSYC 5130 Key Elements X.Liu PSYC 5130 First stop: LGN(Thalamus) X.Liu PSYC 5130 The “Stripes” of Striate Cortex (V1) Vary by Eye of Input LGN neurons separated by eye of input This is maintained in projection to striate cortex (primary visual area, V1) Discovered by Hubel and Wiesel in 1960s X.Liu PSYC 5130 Receptive Fields Become More Complex and Larger as We Ascend Through the Projections X.Liu PSYC 5130 Retinal Ganglion Cell Center-Surround Fields X.Liu PSYC 5130 More Complexity in Cortical Receptive Fields Another important finding by Hubel and Wiesel “Simple” Visual Cortex Cells: Respond to a bar of light in a particular orientation (horizontal, oblique) X.Liu PSYC 5130