perception and vision

• More than 75% of information from both eyes travels back to the thalamus
• The visual system is not like a camera because images seen on one side are processed by the other side of the brain
• Introspection suggests that we perceive things as unified wholes or snapshots like a camera
• Lateral inhibition in visual perception enhances contrast and centers around inhibition, where a neuron's response to a stimulus is inhibited by the excitation of a neighboring neuron
• Visual perception involves an analytic process with several parallel processing streams specialized to extract and process specific elements of visual information
• Visual pathways:

  • Eye: Retina
  • Subcortex: LGN (Dorsal lateral geniculates, ventral lateral geniculate, pulvinar), Brainstem (superior colliculus, pretectum)
  • Cortex: Strait cortex, Posterior Association Cortex
• Optic chiasm is where nerves cross, and information from both eyes is processed, but anything from the left hemifield is processed by the right side of the brain
• Decussation refers to the action of intersecting or crossing, especially in the form of an X
• Layers of the lateral geniculate nucleus (LGN):

  • Magnocellular cells in layers 1 & 2 primarily process information about motion and flicker with good temporal but poor spatial resolution
  • Parvocellular cells in layers 3, 4, 5 & 6 primarily process information about form, color, and texture with poor temporal but great spatial resolution
• Primary Visual Cortex (V1) is subdivided into separate regions called visual cortical areas and processes information from the LGN before passing it to other visual cortical areas
• V1 is composed of hypercolumns that analyze information from small regions of the retina
• Feature channels in the visual system involve different groups of cells working collectively to extract specific features like color and depth
• Visual cortical magnification devotes more processing power to where we are looking, with 20% of the brain devoted to visual processing
• Visual field disorders include quadrantanopia, hemianopsia, and scotoma, each affecting different parts of the visual field
• Visual pathways increase in complexity and size of the respective field, with functional selectivity dividing the pathways into dorsal for where and ventral for what
• Retinotopic mapping maps visual input from the retina to neurons in the visual cortex, with radial and angular activation patterns
• Vision is used as the paradigmatic case to study perception
• Perception can teach us critical principles that the brain uses for computing and help us understand how the brain works at a higher cognitive level
• Introspection suggests that we perceive things as unified wholes or snapshots like a camera, but visual perception involves a more analytic process with several parallel processing streams
• Visual perception involves an analytic process where elements of the visual world are extracted, segmented, recombined, attenuated, enhanced, reach conscious awareness, and can be recognized
• The Hermann grid illusion is explained by the response of retinal ganglion cells with concentric on-off or off-on receptive fields due to lateral inhibition
• The visual pathways include the eye, subcortex, cortex, dorsal and ventral lateral geniculate, pulvinar, superior colliculus, pretectum, retina, and posterior association cortex
• The retinogeniculate visual pathway involves the optic chiasm, optic nerve, optic radiations, and LGN where images seen on one side are processed by the opposite side of the brain
• The LGN contains 6 layers, with layers 1, 4, and 6 containing information from contralateral fibers, and layers 2, 3, and 5 containing information from ipsilateral fibers
• The LGN has magnocellular and parvocellular cells
• The primary visual cortex (V1) is located in the medial occipital lobe of the brain and processes information coming from the LGN before passing it to other visual cortical areas
• V1 is composed of hypercolumns that analyze information from small regions of the retina, with the fovea being overrepresented
• V1 cells have functional properties such as orientation and color selectivity, and binocular integration
• Hypercolumns in V1 represent stereo vision, color, and line (edge) orientation
• Feature channels in V1 work collectively to extract different features like color and depth, with simple and complex cells activated by edges of particular orientations
• Visual cortical magnification devotes more processing power to where we are looking, with 20% of the brain devoted to visual processing
• Visual field disorders like quadranopsia, hemianopsia, and scotoma can occur due to issues in the visual pathways
• Visual pathways increase in complexity, size of the receptive field, and functional selectivity, using a divide and conquer strategy to represent limited analyses of visual information
• Retinotopic mapping involves visual input from the retina to neurons in radial and angular patterns
• Layers 1, 4, and 6 of LGN contain information from the contralateral fibers (blue layers)
• Layers 2, 3, and 5 of LGN contain information from the ipsilateral fibers (red layers)
• Quadrantanopia - stroke - left corner of the brain is obstructed
• Hemianopsia - whole right or left hemisphere is obstructed
• Scotoma - small circle in the middle of your vision is obstructed
• Receives information from both left and right eyes: monocular cells