视觉与大脑课程.pptxVIP

视觉与大脑课程第1页/共41页 Outline (Ch. 3 and Ch. 4) Neurons, Receptive Fields Human BrainFrom Retina to Visual CortexPrimary Visual Cortex (V1)Secondary Visual Cortex (V2) - optional第2页/共41页 Outline (Ch. 3 and Ch. 4) Neurons, Receptive Fields Human BrainFrom Retina to Visual CortexPrimary Visual Cortex (V1)Secondary Visual Cortex (V2)第3页/共41页 Major Division of Human BrainNeurons and Synapses -optionalReceptive FieldsMajor Division of Human BrainVisual Cortex第4页/共41页 NeuronsWhile the fundamental structural unit of the brain is the neuron, the currencyof the brain is the action potential or spike, which travels at conductionvelocities from 1 to 120 meters (3 to 380 feet) per second. If an insulating myelin sheath (signal booster) is wrapped around the axon then the action potential propagates by “jumping” between gaps in the myelin sheath, otherwise the action potential decays exponentially. 第5页/共41页 SynapsesSynapse. Each neuron receives inputs via its dendrites. If these inputs are sufficiently large then an output in the form of an action potential appears in the neuron’s axon. This causes chemical neurotransmitter to be released at the synapses to other neurons. Courtesy Creative Commons.第6页/共41页 Backward retinaThe light rays that contribute to the retinal image have to pass through layer of nerve fibers and the blood vessels before reaching the light-sensitive photoreceptors. 第7页/共41页 Receptive Fields -Tilting the RetinaPhotoreceptors(pixel array)This receptor isshared by twoganglion cellsCables show connections foronly three receptive fieldsGanglion cellseach photoreceptor can belong to about ten receptive fields第8页/共41页 Receptive Fields –Mexican Hat?Ganglion cell receptive fields. (a) On-center/off-surround. (b) Off-center/on-surround. (c) Three-dimensional graph showing the sensitivity to light spots placed in different regions of the receptive field of a cell with an on-center receptive field. The spike in the middle shows where light excites the cell, and the trough