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1、Vision and BrainZhigang Zhu, Herbert G. Kayser Chair ProfessorDepartment of Computer ScienceCUNY City College and Graduate CenterVision and BrainHow We Perceive the World2. Visual BrainAcknowledgmentsn Textbook: Vision and Brain - How We Perceive the World, By James V. Stone, The MIT Pressn Slides:
2、Most of the figures were taken from the textbook (with permission for use in this class). Please do not distribute or use them for other purposesOutline (Ch. 3 and Ch. 4) n Neurons, Receptive Fields & Human Brainn From Retina to Visual Cortexn Primary Visual Cortex (V1)n Secondary Visual Cortex (V2)
3、 - optionalOutline (Ch. 3 and Ch. 4) n Neurons, Receptive Fields & Human Brainn From Retina to Visual Cortexn Primary Visual Cortex (V1)n Secondary Visual Cortex (V2)Major Division of Human Brainn Neurons and Synapses -optionaln Receptive Fieldsn Major Division of Human Brainn Visual CortexNeuronsWh
4、ile 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
5、 potential propagates by “jumping” between gaps in the myelin sheath, otherwise the action potential decays exponentially. 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 neurons a
6、xon. This causes chemical neurotransmitter to be released at the synapses to other neurons. Courtesy Creative Commons.Backward retinan The 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 photorecepto
7、rs. 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 fieldsReceptive Fields Mexican Hat?Ganglion cell receptive fields. (a
8、) 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 around t
9、his spike shows where light inhibits the cell. (d) These cells are sometimes said to have Mexican hat receptive fields.a b c dReceptive Fields Spatial FrequencyNarrow stripes on the zebras front leg correspond to a high spatial frequency, whereas wide stripes on its back leg correspond to a low spat
10、ial frequencyFourier analysis. The complicated curve in (d) is the sum of corresponding pointsin the sinusoidal curves in (ac).Receptive Fields Logans theoremMajor Division of Human BrainOutline (Ch. 3 and Ch. 4) n Neurons, Receptive Fields & Human Brainn From Retina to Visual Cortexn Primary Visual
11、 Cortex (V1)n Secondary Visual Cortex (V2)From Retina to Visual Cortexn A Few Interesting Discoveriesn From Retina to LGNn Layers in the LGNsn From LGN to Striate Cortex (V1) basics onlyA Few Interesting Discoveryn “The dumber the animal, the smarter the retina” (Denis Baylor of Stanford Medical Sch
12、ool, in Montgomery, 1995).n Neurons, known as “bug detectors,” that respond almost exclusively to the erratic motion of a fly are synthesized in retinal ganglion cells (Lettvin et al. 1959)n Most of the computational machinery responsible for vision in the frog resides in the retina.n The human brai
13、n delays detailed analysis of the retinal image until after the information has left the retina via the optic nerve. While this is true, it is not the whole truth.n The decomposition of the retinal image into key components, such as color and motion, begins at the retina.From Retina to LGN How the v
14、isual world gets transformed by the pathways of the visual system. Modifiedfrom Frisby & Stone 2010.n Cross-over Similar visual hemifieldn LGN: lateral geniculate nuclei Left and right 6 layersLayers in the LGNsLeft LGN: R, L, R, L, L, R retinas Right LGN: L, R, L, R, R, L retinasRather than using t
15、he labels L and R, a more general terminology is ipsilateral (I) and contralateral (C), so both have C, I, C, I, I, CMagno layers 1 and 2 at the base (from rods and 10% ganglion cells with large receptive fields, so low-luminance, B-W and magno (M) processing stream for motion) Parvo layers 36 at th
16、e top (from cones and 80% ganglion cells with small receptive fields, so R/G color and parvo (P) processing stream for spatial and static forms). At the base of each magno and parvo layer, a thinner konio layer from 10% of ganglion cells responding to blue (B) and yellow.From LGN to Striate Cortex (V1)Mac
