Vision The Receptors: Their Structure & Development
General Principles of Perception <ul><li>Each Receptor is Specialized to Absorb One Kind of Energy & Transduce it into an ...
The Eye/Brain Connection <ul><li>Structure </li></ul><ul><li>Light enters the eye through the Cornea & the Pupil </li></ul...
The Fovia & the Periphery of the Retina <ul><li>Macula </li></ul><ul><li>Portion of the Retina with the greatest ability t...
Visual Receptors <ul><li>Rods </li></ul><ul><li>Abundant in the periphery of the Retina </li></ul><ul><li>For Periphery & ...
C o l o r   V i s i o n <ul><li>Requires Comparing Responses of Different Kinds of Cones </li></ul><ul><li>Shortest to Lon...
C o l o r   V i s i o n <ul><li>Retinex Theory (The Land Effect) </li></ul><ul><li>Proposed to account for  Color Constanc...
Colorblindness <ul><li>Color Vision Deficiency </li></ul><ul><li>Seen mostly in Males </li></ul><ul><li>Red-Green colorbli...
The Visual System <ul><li>Rods & Cones Synapse with Horizontal & Bipolar Cells </li></ul><ul><li>Horizontal cells make  in...
Mechanisms of Visual Processing <ul><li>Receptive Fields </li></ul><ul><li>Visual Field </li></ul><ul><li>The area of the ...
Neurons in the Visual Pathways <ul><li>Parvocellular Neurons </li></ul><ul><li>Small cell bodies located in or near the fo...
In the Cerebral Cortex <ul><li>Most Axons from the LGN go 1 st  to the Primary Visual Cortex (V1) </li></ul><ul><li>V1 sen...
Object Recognition <ul><li>Ventral Stream </li></ul><ul><li>Made up of parvocellular & magnocelluilar pathways </li></ul><...
Categories of Neurons in the Cerebral Cortex <ul><li>Simple Cells </li></ul><ul><li>Neurons with fixed excitatory & inhibi...
Recognition of Shape <ul><li>Cells in the Visual Cortex are in Columns </li></ul><ul><li>Set perpendicular to the surface ...
Disorders of Object Recognition <ul><li>Visual Agnosia </li></ul><ul><li>The inability to recognize objects despite otherw...
Color, Motion, & Depth <ul><li>Color Perception Depends on Parvocellular & Koniocellular Pathways </li></ul><ul><li>Blobs ...
Stereoscopic Depth Perception The ability to detect depth is by differences in the 2 eyes Many cells in the Magnocellular ...
Creating Stereo Images <ul><li>Anaglyph 3-D </li></ul><ul><li>Uses red/blue lenses on glasses </li></ul><ul><li>Cross-eyed...
Stereo Images
Motion Detection <ul><li>Medial Temporal Cortex </li></ul><ul><li>Middle Temporal Cortex & Medial Superior Temporal Cortex...
<ul><li>Importance of V1 Area </li></ul><ul><li>Activation & feedback to V1 area necessary for attention or conscious awar...
Development of the Visual System <ul><li>Infant Vision </li></ul><ul><li>Infants have better vision than once imagined </l...
The Effects of Experience <ul><li>Lack of Early Stimulation </li></ul><ul><li>In One Eye: Most neurons in the Visual  Cort...
Restoring Response after Early Deprivation <ul><li>Depends on When </li></ul><ul><li>If normal experiences begun soon enou...
Stimulation in Both Eyes <ul><li>Retinal Disparity </li></ul><ul><li>The discrepancy between the left & the right eye sees...
Astigmatism <ul><li>Blurring of Vision in One Direction </li></ul><ul><li>Caused by an asymmetric curvature of the eyes </...
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Chapter 06: Vision

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

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Transcript of "Chapter 06: Vision"

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