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1、Vision and BrainZhigang Zhu, Herbert G. Kayser Chair Professor Department of Computer Science CUNY City College and Graduate CenterVision and Brain How We Perceive the World2. Visual BrainAcknowledgmentsnTextbook: Vision and Brain - How We Perceive the World, By James V. Stone, The MIT PressnSlides:
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) nNeurons, Receptive Fields F = fovea; I = inferior (lower) visual field; H = horizontal meridian. Reproduced with modifications f
3、rom Tootell et al. 1988.From LGN to Striate Cortex (V1)nThe neocortex is sheet of neurons, a 1.7 mm thick and 1,300 cm2 in area, that constitutes the outermost part of the two cerebral hemispheres of the brain. nEvery mm3 of neocortex contains 100,000 neurons, and the whole neocortex contains a tota
4、l of approximately 25 billion neurons, each of which receives inputs via 4,000 synapses.nThe global structure of the visual cortex is organized retinotopically; that is, adjacent points in the retinal image usually project to adjacent points in striate cortexnNote that the central foveal region of t
5、he retina projects to a relatively large area in the LGNs and striate cortex.From LGN to Striate Cortex (V1)Unpacking the striate cortex. The outputs of different ganglion cells in each eye project to specific layers of the LGNs (C = contralateral, I = ipsilateral). These then project to striate cor
6、tex (V1), which project to discrete stripes of V2. These project to areas V3 V5, which are specialized for processing different types of information.From LGN to Striate Cortex (V1)nThe division of labor that began with the different types of photoreceptors and continued with the retinal ganglion cel
7、ls and the LGNs extends into the primary visual cortex. nSpecifically, the projections of the magnocellular LGN layers terminate in a sublayer of layer 4 (4C), whereas projections of the parvocellular LGN layers terminate in sublayer (4C)nCollaterals (subbranches) of the axons from cells in the LGN
8、also innervate the pyramidal cells in cortical layer 6,which send projections back to the LGN cells that innervate them.From LGN to Striate Cortex (V1)Monkey striate cortex. Microscopic enlargements of sections stained to emphasize cell bodies in (a) and nerve fibers in (b). The numbers at the right
9、 refer to various layers that can be distinguished microscopically. Courtesy LeVay, Hubel, and Wiesel (1975).From LGN to Striate Cortex (V1)nThere is a complete, and quite specific, set of feedback connections from striate cortex to LGNs. nIn fact, most of the input connections to the LGN come, not
10、from the retina, but from these V1 feedback connections.nThe function of these connections is not known, but interfering with them seems to decrease the specificity of LGN cells.Outline (Ch. 3 and Ch. 4) nNeurons, Receptive Fields they also respond to other parameters, especially stereo disparitynJu
11、st as V4 has reduced retinotopy (point-for-point mapping of cortical to retinal neurons), so the relative lack of retinotopy in V5 may exemplify how the purely spatial primary index apparent in V1 (striate cortex) and V2 may be replaced by the non-spatial primary index of motion in V5.Losing Retinot
12、opynAlthough theres little doubt that the striate cortex provides a reasonably accurate map of the retinal image, other visual areas seem to supplant this retinotopy with some other property.nOne explanation for this loss of retinotopy is that the primary and secondary indexes gradually swap places
13、as we move away from the striate cortex.From space index to indices in color, motion, disparity, etc.Inferotemporal Cortex (grandmother cell)nWhat if different cells responded to different views of your grandmother, and what if the outputs of all these cells converged on a single cell?nThe view-sele
14、ctive cortical cells describe above may also be organized according to temporal context.nOther high-order features that seem to be in inferotemporal cortex include hands, faces, walking humans, and objectsEach point in a small region of inferotemporal cortex seems to represent a different view of a face. But perhaps the most surprising finding is that nearby cells respond to similar views of the face.Outline (Ch. 3 and Ch. 4) nNeurons, Receptive Fields & Human BrainnFrom Retina to Visual CortexnPrimary Visual Cortex (V1)nSecondary Visual Cortex (V2)
