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Chapter 06: Vision
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Chapter 06: Vision


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Principles of perception, neurological basis of visual perception, and the brain and vision.

Principles of perception, neurological basis of visual perception, and the brain and vision.

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  • 1. Vision The Receptors: Their Structure & Development
  • 2. General Principles of Perception
    • Each Receptor is Specialized to Absorb One Kind of Energy & Transduce it into an Electrochemical Pattern in the Brain
    • Coding of visual information in the brain does not duplicate the shape of the object
    • Law of Specific Nerve Energies
    • Any activity by a particular nerve always conveys the same kind of information to the brain
    Visual Receptors Respond to as Little as 1 Photon of Light Light is transduced into a Receptor Potential
  • 3. The Eye/Brain Connection
    • Structure
    • Light enters the eye through the Cornea & the Pupil
    • It is focused by the Cornea & Lens & projected on to the Retina
    • Retina
    • The rear surface of the eye which is lined with visual receptors
    • The Route
    • Receptors send messages to the Bipolar Cells , which send messages to Ganglion Cells
    • Amacrine Cells are important for complex processing of visual information
    • Ganglion Cells join together to form the Optic Nerve
  • 4. The Fovia & the Periphery of the Retina
    • Macula
    • Portion of the Retina with the greatest ability to resolve detail
    • Fovea
    • Central potion of the Macula specialized for acute, detailed vision
    • Fovea has the least impeded vision
    • Each receptor connects to a single Bipolar Cell which connects to a single Ganglion Cell
    • Midget Ganglion Cells
    • Receive input from a single cone
    • Each cone has a direct line to the brain
  • 5. Visual Receptors
    • Rods
    • Abundant in the periphery of the Retina
    • For Periphery & Night Vision
    • Cones
    • Primarily in the Fovea
    • For Visual Acuity & Color Vision
    • Photopigments: Chemicals that release energy when struck by light
  • 6. C o l o r V i s i o n
    • Requires Comparing Responses of Different Kinds of Cones
    • Shortest to Longest Wavelengths
    • Shortest wavelength seen as Violet, longest wavelengths seen as Blue, Green, Yellow, & Red
    • Two Main Theories
    • Trichromatic Theory
    • Opponent-process Theory
  • 7. C o l o r V i s i o n
    • Retinex Theory (The Land Effect)
    • Proposed to account for Color Constancy
    • When information from various parts of the retina reaches the cortex, the cortex compares each of the inputs to determine the brightness & color perception for each area
    Shades of Red Adding Yellow
  • 8. Colorblindness
    • Color Vision Deficiency
    • Seen mostly in Males
    • Red-Green colorblindness is most common
    • On the X-chromosome
    • X-linked disorder
  • 9. The Visual System
    • Rods & Cones Synapse with Horizontal & Bipolar Cells
    • Horizontal cells make inhibitory contact onto bipolar cells which synapse with amacrine and ganglion cells
    • Axons of the Ganglion Cells Form the Optic Nerve
    • Optic nerves from both eyes meet at the optic chiasm where ½ of the axons from each eye cross to the opposite side of the brain
    • Most of the ganglion cells go to the Lateral Geniculate Nucleus of the thalamus
  • 10. Mechanisms of Visual Processing
    • Receptive Fields
    • Visual Field
    • The area of the world that you can see at any time
    • Receptive Field
    • The portion of the visual field to which any neuron responds
    • Lateral Inhibition
    • The reduction of activity in one neuron by activity in neighboring neurons
    • This is the retinal technique that sharpens the boundaries of visual objects
  • 11. Neurons in the Visual Pathways
    • Parvocellular Neurons
    • Small cell bodies located in or near the fovea with small receptive fields & respond best to details & color
    • They synapse only onto cells of the LGN
    • Magnocellular Neurons
    • Larger cell bodies distributed throughout the retina & have a larger receptive field responding best to moving stimuli
    • Most synapse onto cells of the LGN, but a few connect to other areas of the Thalamus
    • Koniocellular Neurons
    • Similar in size to Parvocellular Neurons, but distributed throughout the retina
    • They have several different functions & their axons connect to the LGN, other areas of the Thalamus, & the Superior Colliculus
  • 12. In the Cerebral Cortex
    • Most Axons from the LGN go 1 st to the Primary Visual Cortex (V1)
    • V1 sends information to the Secondary Visual Cortex (V2)
    • Connections between V1 & V2 are reciprocal
    • In the cortex, Parvocellular & Magnocellular pathways split from 2 to 3 pathways
    • Parvocellular is sensitive to shape
    • Magnocellular is sensitive to movement
    • The mixed pathway is sensitive to brightness & color
  • 13. Object Recognition
    • Ventral Stream
    • Made up of parvocellular & magnocelluilar pathways
    • Goes through V1, V2, V4 & areas of the Inferior Temporal Lobe
    • Sensitive to shape, movement & color brightness
    • Specialized for object recognition & identification
    • Dorsal Stream
    • Mostly magnocellular pathways
    • From V1 to Parietal & to Temporal Lobes
    • Integrates vision & movement leading to the Parietal Lobe
  • 14. Categories of Neurons in the Cerebral Cortex
    • Simple Cells
    • Neurons with fixed excitatory & inhibitory zones in their receptive fields
    • Found only in the Primary Visual Cortex (V1)
    • Complex Cells
    • Receive input from a combination of Simple Cells
    • Have receptive fields that respond to particular orientations of light but cannot be mapped into fixed excitatory & inhibitory zones
    • Located in V1 or V2
    • End-stopped (Hyper-complex) Cells
    • Strongly resemble complex cells but have an inhibitory area at one end of its bar-shaped receptive field
  • 15. Recognition of Shape
    • Cells in the Visual Cortex are in Columns
    • Set perpendicular to the surface according to response orientation
    • Feature Detectors
    • Neurons whose responses indicate the presence of a particular feature
    • Inferior Temporal Cortex
    • Provides information about complex shaped stimuli
    • Important in Shape Constancy
  • 16. Disorders of Object Recognition
    • Visual Agnosia
    • The inability to recognize objects despite otherwise normal vision
    • Prosopagnosia
    • The inability to recognize faces without an overall loss of vision or memory
    • The Fusiform Gyrus in the Inferior Temporal Cortex is specialized for face recognition
    • This area is also activated when identifying car models, bird species, and so on
  • 17. Color, Motion, & Depth
    • Color Perception Depends on Parvocellular & Koniocellular Pathways
    • Blobs
    • Patches of cells in V1 highly sensitive to color areas
    • Includes Parvocellular & Koniocellular neurons for color & Magnocellular for brightness
    • Output is sent to V2, V4, & Posterior Inferior Temporal Cortex
  • 18. Stereoscopic Depth Perception The ability to detect depth is by differences in the 2 eyes Many cells in the Magnocellular Pathway are specialized for Depth Perception
  • 19. Creating Stereo Images
    • Anaglyph 3-D
    • Uses red/blue lenses on glasses
    • Cross-eyed 3-D
    • Must cross eyes to create a single image or use lenses that create the image
    • Polarized Lens 3-D
    • Use of polarized lenses on glasses
  • 20. Stereo Images
  • 21. Motion Detection
    • Medial Temporal Cortex
    • Middle Temporal Cortex & Medial Superior Temporal Cortex important in motion detection
    • Mechanisms to Distinguish between Moving Objects & Head Changes
    • Damage to Medial Temporal Cortex results in motion blindness
  • 22.
    • Importance of V1 Area
    • Activation & feedback to V1 area necessary for attention or conscious awareness of a stimulus
    • Binding Necessary for Consciousness
    • Synchronized activity of the 2 hemispheres necessary to see something that crosses the midline of vision as a single object
    • A limited amount of visual processing takes place without being conscious
    • Blindsight
    • Some people with extensive damage to V1 can localize visual objects with a blind visual field
    Visual Attention & Consciousness
  • 23. Development of the Visual System
    • Infant Vision
    • Infants have better vision than once imagined
    • Spend more time looking at faces, circles, or stripes than at patternless displays
    • They have trouble shifting their gaze until about 6 months
  • 24. The Effects of Experience
    • Lack of Early Stimulation
    • In One Eye: Most neurons in the Visual Cortex receive binocular input. Deprivation leads to blindness in the one eye
    • In Both Eyes: If both eyes are deprived of stimulation, cortical cells will remain sluggishly responsive in both eyes
    • People born blind but acquiring vision later have trouble identifying shapes & objects & find newly gained vision almost useless
    • Sensitive or Critical Period
    • A stage of development when experiences have a particularly strong & long-lasting influence
    • Effects of abnormal experiences on cortical development depend on the length of the sensitive period
    • In humans, even a brief abnormal experience can result in deficits
  • 25. Restoring Response after Early Deprivation
    • Depends on When
    • If normal experiences begun soon enough, sensitivity can be restored
    • Amblyopia
    • Lazy Eye, can be treated by putting a patch over the active eye
  • 26. Stimulation in Both Eyes
    • Retinal Disparity
    • The discrepancy between the left & the right eye sees
    • It is necessary for stereoscopic depth perception
    • The fine-tuning of binocular vision depends on experience
    • Strabismus
    • The eyes do not point in the same direction
    • Cannot perceive depth better with 2 eyes as opposed to 1
  • 27. Astigmatism
    • Blurring of Vision in One Direction
    • Caused by an asymmetric curvature of the eyes
    • Corrective lenses in early childhood improve the vision
    • Early Blind
    • Certain portions of the Visual Cortex in people blind early in life become responsive to auditory or touch stimuli