Psychology 355 The Visual System

Psychology 3552 Introduction I.Neurons in the visual system A.Neural processing resulting in perception II.Parallel pathway serving conscious visual perception originate in the retina A.Progress to lateral geniculate nucleus, primary visual cortex & higher order visual areas in temporal and parietal lobes III.Neuronal receptive fields A.Sensitive to different facets of the visual input

Psychology 3553 The Retinofugal Projection The Optic Nerve, Optic Chiasm, Optic Tract

Psychology 3554 The Retinofugal Projection The Optic Nerve, Optic Chiasm, Optic Tract, LGN, Optic Radiations

Psychology 3555 The Retinofugal Projection I.Right and Left Visual Hemifields

Psychology 3556 The Retinofugal Projection Targets of the Optic Tract

Psychology 3557 The Retinofugal Projection Targets of the Optic Tract

Psychology 3558 The Retinofugal Projection Targets of the Optic Tract

Psychology 3559 The Retinofugal Projection I.Nonthalamic Targets of the Optic Tract: A.Hypothalamus: Biological rhythms, including sleep and wakefulness B.Pretectum: Size of the pupil; certain types of eye movement C.Superior colliculus: Orients the eyes in response to new stimuli

Psychology The Lateral Geniculate Nucleus (LGN)

Psychology The Lateral Geniculate Nucleus (LGN)

Psychology The Lateral Geniculate Nucleus (LGN) I.The Segregation of Input by Eye and by Ganglion Cell Type

Psychology The Lateral Geniculate Nucleus (LGN) I.Receptive Fields A.Receptive fields of LGN neurons: Identical to the ganglion cells that feed them A.Magnocellular LGN neurons: Large, monocular receptive fields with transient response A.Parvocellular LGN cells: Small,monocular receptive fields with sustained response

Psychology The Lateral Geniculate Nucleus (LGN) I.Nonretinal Inputs to the LGN A.Retinal ganglion cells axons: Not the main source of synaptic input to the LGN B.Primary visual cortex: 80% of the synaptic inputs C.Neurons in the brain stem: Modulatory influence on neuronal activity

Psychology Anatomy of the Striate Cortex

Psychology Anatomy of the Striate Cortex

Psychology Anatomy of the Striate Cortex I.Retinotopy A.Map of the visual field onto a target structure (retina, LGN, superior colliculus, striate cortex) - overrepresentation of central visual field B.Discrete point of light: Activates many cells in the target structure C.Perception: Based on the brain’s interpretation of distributed patterns of activity

Psychology Anatomy of the Striate Cortex I.Retinotopy

Psychology Anatomy of the Striate Cortex I.Lamination of the Striate Cortex A.Layers I - VI B.Spiny stellate cells: Spine-covered dendrites; layer IVC C.Pyramidal cells: Spines; thick apical dendrite; layers III, IV, V, VI A.Inhibitory neurons: Lack spines; All cortical layers; Forms local connections

Psychology Anatomy of the Striate Cortex Inputs to the Striate Cortex A.Magnocellular LGN neurons: Project to layer IVC B.Parvocellular LGN neurons: Project to layer IVC

Psychology Anatomy of the Striate Cortex I.Ocular Dominance Columns

Psychology Anatomy of the Striate Cortex I.Inputs to the Striate Cortex A.Layer IVC innervates superficial layers

Psychology Anatomy of the Striate Cortex I.Outputs of the Striate Cortex: A.Layers II, III, and IVB: Projects to other cortical areas B.Layer V: Projects to the superior colliculus and pons C.Layer VI: Projects back to the LGN

Psychology Anatomy of the Striate Cortex I.Cytochrome Oxidase Blobs A.Cytochrome oxidase is a mitochondrial enzyme used for cell metabolism B.Blobs: Cytochrome oxidase staining in cross sections of the striate cortex

Psychology Physiology of the Striate Cortex I.Receptive Fields A.Layer IVC: Monocular; center-surround B.Layer IVC: Insensitive to the wavelength C.Layer IVC: Center-surround color opponency II.Binocularity A.All layers superficial to IVC: First binocular receptive fields in the visual pathway

Psychology Physiology of the Striate Cortex Receptive Field Simple Cells Orientation Selectivity

Psychology Physiology of the Striate Cortex Receptive Field Simple Cells Orientation Selectivity

Psychology Physiology of the Striate Cortex Receptive Field Simple Cells Orientation Selectivity

Psychology Physiology of the Striate Cortex I.Receptive Fields A.Simple cells: Binocular; Orientation- selective; Elongated on-off region with antagonistic flanks responds to optimally oriented bar of light B.Possibly composed of three LGN cell axons with center-surround receptive fields

Psychology Physiology of the Striate Cortex Receptive Fields Complex Cells Direction Selectivity Neuron fires action potentials in response to moving bar of light

Psychology Physiology of the Striate Cortex Receptive Fields Complex Cells Direction Selectivity

Psychology Physiology of the Striate Cortex I.Receptive Fields A.Complex cells: Binocular; Orientation- selective; ON and OFF responses to the bar of light but unlike simple cells, no distinct on-off regions

Psychology Physiology of the Striate Cortex I.Receptive Fields A.Blob Receptive Fields 1.Blob cells: Wavelength- sensitive; Monocular; No orientation; direction selectivity

Psychology Physiology of the Striate Cortex Parallel Pathways: Magnocellular Parvocellular Koniocellular

Psychology Physiology of the Striate Cortex Cortical Module

Psychology Striate Cortex: Summary Type LayerInput I IIKoniocellular, IVCα, IVCβ Orientation (simple) Color (blobs) Binocular (III) V2, V3, V4, Pyramidal III IVA Pyramidal IVBIVCαMotion (complex) V2, V5(MT) Spiney IVCαMagnocellularIVB, II, III Spiney IVCβParvocellularII, III Pyramidal VColliculus Pyramidal VILGN }

Psychology Beyond Striate Cortex I.Dorsal stream A.Analysis of visual motion and the visual control of action II.Ventral stream A.Perception of the visual world and the recognition of objects

Psychology Beyond Striate Cortex I.The Dorsal Stream (V1, V2, V3, MT, MST, Other dorsal areas) A.Area MT (temporal lobe) 1.Most cells: Direction-selective; Respond more to the motion of objects than their shape B.Beyond area MT - Three roles of cells in area MST (parietal lobe) i.Navigation ii.Directing eye movements iii.Motion perception

Psychology Beyond Striate Cortex I.The Ventral Stream (V1, V2, V3, V4, IT, Other ventral areas) A.Area V4 1.Achromatopsia: Clinical syndrome in humans-caused by damage to area V4; Partial or complete loss of color vision B.Area IT 1.Major output of V4 2.Receptive fields respond to a wide variety of colors and abstract shapes

Psychology From Single Neurons to Perception I.Visual perception A.Identifying & assigning meaning to objects II.Hierarchy of complex receptive fields A.Retinal ganglion cells: Center-surround structure, Sensitive to contrast, and wavelength of light B.Striate cortex: Orientation selectivity, direction selectivity, and binocularity C.Extrastriate cortical areas: Selective responsive to complex shapes; e.g., Faces

Psychology From Single Neurons to Perception I.From Photoreceptors to Grandmother Cells A.Grandmother cells: Face-selective neurons in area IT? B.Probably not: Perception is not based on the activity of individual, higher order cells II.Parallel Processing and Perception A.Groups of cortical areas contribute to the perception of color,motion, and identifying object meaning

Psychology Concluding Remarks I.Vision A.Perception combines individually identified properties of visual objects B.Achieved by simultaneous, parallel processing of several visual pathways II.Parallel processing A.Like the sound produced by an orchestra of visual areas rather than the end product of an assembly line

Psychology 355 End of Presentation