Central Visual Processing Chapter 10 PDF

Central Visual Processing Chapter 10   Discuss the complex processing pathways of visual information in the brain  Eye   LGN  Learning  V1 / striate cortex  objectives  Beyond V1 (dorsal/ventral streams)...

Central Visual Processing Chapter 10   Discuss the complex processing pathways of visual information in the brain  Eye   LGN  Learning  V1 / striate cortex  objectives  Beyond V1 (dorsal/ventral streams)  Focus on major anatomical landmarks as key “stations” along the pathway  Know what new vocab words actually mean! Introduction Introduction Introduction  Vision  Perception combines individually identified properties of visual objects: color, form, movement  Achieved by simultaneous, parallel processing in several visual pathways  Parallel processing  More like the sound produced by an orchestra than by individual musicians   Neurons in the visual system  Neural processing results in perception.  Pathway serving conscious visual perception originates in the Central visual retina. processing  Progresses to lateral geniculate nucleus, primary visual cortex, pathway and higher order visual areas in occipital, temporal, and parietal lobes  Overlapping receptive fields  Sensitive to different facets of visual input   Left hemifield projects to right side of brain. (& vice versa)  Ganglion cell axons from nasal retina cross in optic chiasm. Right & left visual hemifields   Left hemifield projects to right side of brain. (& vice versa)  Ganglion cell axons from nasal retina cross in optic chiasm. Right & left visual hemifields   Left hemifield projects to right side of brain. (& vice versa)  Ganglion cell axons from nasal retina cross in optic chiasm. Right & left visual hemifields   Hypothalamus: role in biological rhythms, including sleep and wakefulness Nonthalamic  Pretectum: control size of the pupil, certain types of eye targets of movement optic tract  Superior colliculus: orients the eyes in response to new stimuli— move fovea to objects of interest   Six layers in the lateral geniculate nucleus of the Retinal inputs thalamus to LGN layers  Not random – top layers and bottom layers have different functions!   Inputs segregated by eye and ganglion cell type  Parvocellular layers for color vision processing  Magnocellular layers for non-color vision processing  Koniocellular layers function are a bit of a mystery Organization of the LGN   Receptive fields of LGN neurons: almost identical to the ganglion cells that feed them LGN  Magnocellular LGN neurons: receptive large center-surround receptive fields with transient response fields  Parvocellular LGN cells: small center-surround receptive fields with sustained response   Primary visual cortex (also called V1, striate cortex, or Brodmann area 17) provides 80% of the synaptic input to Nonretinal the LGN—role not clearly identified. inputs to the  “Top–down” modulation may gate “bottom-up” input LGN from LGN back to cortex.  Brain stem neurons provide modulatory influence on neuronal activity.   Primary visual cortex (also called V1, striate cortex, or Brodmann area 17) provides 80% of the synaptic input to Nonretinal the LGN—role not clearly identified. inputs to the  “Top–down” modulation may gate “bottom-up” input LGN from LGN back to cortex.  Brain stem neurons provide modulatory influence on neuronal activity.   Retinotopic map of the visual field onto a target structure (retina, LGN, superior colliculus, striate cortex)  Central visual field (fovea) overrepresented in map  Discrete point of light can activate many cells in the target structure due to overlapping receptive fields.  Perception is based on the brain’s interpretation of distributed patterns of activity—not a literal map as in a picture. Retinotopy   Striate cortex (V1, primary visual cortex) has six layers as well Layers of the striate cortex   Layers I to VI  Spiny stellate cells: spine-covered Layers of the dendrites—layer IVC striate cortex  Pyramidal cells: spines and thick apical dendrite—layers III, IVB, V, VI  Inhibitory neurons: lack spines—all cortical layers—form local connections   Magnocellular LGN neurons project primarily to layer IVC. Inputs to the  Parvocellular LGN neurons project to striate cortex layer IVC.  Koniocellular LGN axons make synapses primarily in layers I and III.   Studied with transneuronal autoradiography from retina, to LGN, to striate cortex  Preferential information processing from one eye  Unsure if bug or feature evolutionarily! Ocular dominance columns   Studied with transneuronal autoradiography from retina, to LGN, to striate cortex  Preferential information processing from one eye  Unsure if bug or feature evolutionarily!  Binocular deprivation can make them go away! Ocular dominance columns Mixing  First binocular neurons information found in striate cortex— most layer III neurons are from both binocular (but not layer IV). eyes   Layer II, III, and IVB cells project to other cortical areas. Outputs of the  Layer V cells project to the superior striate cortex colliculus and pons.  Layer VI cells project back to the LGN.   Cytochrome oxidase: mitochondrial enzyme used for cell metabolism  Blobs: cytochrome oxidase- stained pillars in striate cortex Cytochrome  Each blob centered on an ocular dominance column in layer IV. oxidase blobs  Receive koniocellular inputs from LGN  Likely important for color vision processing since they are made of color wavelength-sensitive cells   Monocular receptive fields  Layer IVC: similar to LGN cells  Layer IVC: insensitive to the wavelength Physiology of  Layer IVC: center- surround color opponency striate cortex  Binocular receptive fields – orientation  Most neurons in layers superficial to IVC are selectivity binocular.  Two receptive fields—one for each eye  Receptive fields help distinguish orientation selectivity   Receptive fields help to distinguish motion & direction selectivity  Neuron fires action potentials in direction-dependent response to moving bar of light. Physiology of striate cortex – direction selectivity   Simple cells: binocular, orientation-selective, elongated ON or OFF area flanked with antagonistic surround  Not necessarily restricted to 1 V1 layer, but most ly found in layers 4 and 6  Receptive field may be composed of three LGN inputs from cells with aligned center-surround receptive fields. Simple cell  Great for edge/border/shape detection receptive fields   Complex cells: binocular, orientation-selective, ON and OFF responses to the bar of light but unlike simple cells, no distinct ON and OFF regions  Also not confined to a single V1 layer, many found in layer 3  Better for movement/rotation detection Complex cell receptive fields   Some blob fields  Monocular  No direction selectivity  Likely orientation selectivity  Variety of color opponency and surround organization  Specialized for analysis of color Blob receptive fields?   Magnocellular, blob, and parvo-interblob pathways all simultaneously contribute to visual perception  Parallel processing  More like the sound produced by an orchestra than by individual musicians Parallel processing pathways   “Chunk” of striate cortex containing all the layers and cells needed to process a full spectrum of visual information  Each module capable of analyzing every aspect of a portion of the visual field Cortical modules   Occipital cortex contains many Visual areas visual processing areas that add of the brain onto the depth of information coming from V1 beyond V1  Adding on details like texture, color gradients, etc   Dorsal stream Dorsal and  Analysis of visual motion and the visual control of action ventral visual  Ventral stream streams  Perception of the visual world and the recognition of objects   V1, V2, V3, MT, MST, other dorsal areas  Area MT (temporal lobe)  Most cells are direction-selective, respond more to the motion of objects Dorsal visual than their shape. stream  Beyond area MT—three roles proposed for cells in area MST (parietal lobe)  Navigation  Directing eye movements  Motion perception   V1, V2, V3, V4, IT, other ventral areas  Area V4—shape and color perception  Achromatopsia: clinical syndrome caused by damage to area V4—partial or complete loss of color vision Ventral visual  Area IT stream  Major output of V4  Receptive fields respond to a wide variety of colors and abstract shapes.  May be important for both visual perception and visual memory (such as faces)   Visual perception  Identifying and assigning meaning to objects  Hierarchy of complex receptive fields  In retinal ganglion cells: center-surround structure, sensitive to contrast and wavelength of light  In striate cortex: orientation selectivity, direction selectivity, and Parallel binocularity  Extrastriate cortical areas: selective responsive to complex shapes processing & (faces) and motion perception The  “Grandmother cells” / “Halle Berry” cells? neuroscience  Specific face-selective of vision is neurons in area IT?  Probably not: perception very complex; not based on the activity of individual cells be wary of  Parallel processing and reductive perception  Groups of cortical areas descriptions contribute to the perception of color, motion, and object of it! meaning. Optical illusions “hack” our visual processing quirks Quiz hint!  LGN layers & cell types Questions?