OUTLINE Light The Eye Flow of Visual Information Optic Nerve Left and right visual fields from each eye projected to the right and left hemispheres respectively About 50 of fibers cross to opposite hemisphere Optic Nerve Connections Optic Nerve Connections A small number of axons from each eye also project to the suprachiasmatic nucleus a structures that regulates the sleep wake cycle based on incoming light information Visual Processing Pathways Retinal Targets Superior colliculus Located in midbrain Guides head and eye movements 10 of optic tract axons Lateral Geniculate Nucleus LGN Located in thalamus Projects to primary visual cortex V1 Visual perception 90 of optic tract axons Lateral Geniculate Nucleus Has antagonistic center surround receptive fields Lateral Geniculate Nucleus About 80 of the input to LGN comes from primary visual cortex Allows cortex to modify its own visual input based on organism s state of arousal or attentiveness Optic Nerve Connections Primary Visual Cortex Striate Cortex V1 Receives projections from the LGN Located in the occipital lobe Convergence Divergence LGN Input Primary Visual Cortex Striate Cortex V1 Cortical Receptive Fields Visual information processed by two cell types Simple cortical cells Complex cortical cells Primary Visual Cortex Striate Cortex V1 Simple cortical cells respond to object shape Response is for particular line orientation Cortical Receptive Fields Simple Cortical Cell Receptive fields maintain antagonistic center surround Shape of receptive field elongated Respond to stimuli shaped like bars or edges that have a particular slant or orientation Retinotopic mapping Cortical Receptive Fields Complex Cortical Cell Larger receptive fields No off regions Shows preferred stimulus size and orientation but not location within the visual field Retinotopic mapping Sensitive to movement Perception of movement Columnar Organization of Primary Visual Cortex Orientation Column Responds to lines of a single angle for single eye Ocular Dominance Column Responds to input from either the left or right eye but not both Preferred orientation changes Columnar Organization of Primary Visual Cortex Orientation Column Ocular Dominance Column Primary Visual Cortex Orientation simple cortical cells Movement complex complex cells Color Blobs Blob like masses of cells that respond to color Cortical Module Integration of decomposed visual field 1000 modules each 2 x 2 mm 8 10 of all modules devoted to input from fovea Visual Association Cortex Aka secondary visual cortex extrastriate cortex Consists of at least 2 dozen distinct areas Each is specialized to respond to particular features of the environment Organized hierarchically moving up the hierarchy the receptive fields become larger and the stimuli to which they respond more complex What and Where Pathways The Dorsal where Stream Motion recognition The Ventral what Stream Object recognition Dorsal where pathway Magnocellular Specialized for movement locating objects and visual control of skilled actions Better thought of as how stream provides info on how to interact with object Akinetopsia Motion blindness Damage at the occipital parietal junction Extremely rare but several case studies Ventral what pathway Parvocellular Responds to shapes different forms and color Associated with storage of long term memory Fusiform Facial Area Part of the ventral stream Located within fusiform gyrus of inferior temporal lobe Responds predominantly to faces and members of learned categories e g species of birds Face Perception Social animals seem uniquely attuned to faces Face Perception Social animals seem uniquely attuned to faces Thatcher Effect Face Perception Social animals seem uniquely attuned to faces Prosopagnosia Face blindness Injury or congenital 1 3 of population Prosopagnosia Face blindness Injury or congenital 1 3 of population
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