1. Copyright (c) Allyn & Bacon 20041 Chapter 6 Vision This multimedia product and its contents are protected under copyright law. The following are prohibited by law: any public performance or display, including transmission of any image over a network, preparation of any derivative work, including the extraction, in whole or in part, of any images; any rental, lease or lending of the program.

2. Copyright (c) Allyn & Bacon 20042  Vision  Sensory receptor: A specialized neuron that detects a particular category of physical events.

3. Copyright (c) Allyn & Bacon 20043  The Stimulus  Perceived color of light is determined by:  Hue:  Determined by wavelength  Saturation:  Determined by the purity of the light wave  Brightness:  Determined by the intensity of the electromagnetic radiation

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6. Copyright (c) Allyn & Bacon 20046  Anatomy of the Visual System  The Eyes  Orbits:  Bony pockets in the front of the skull  Sclera:  The white tissue of the eye  Conjunctiva:  Mucus membranes that line the eyelid and protect the eye

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9. Copyright (c) Allyn & Bacon 20049  Anatomy of the Visual System  The Eyes  Cornea:  Transparent outer covering of the eye that admits light  Pupil:  Adjustable opening in the iris that regulates the amount of light that enters the eye  Iris:  Pigmented ring of muscles situated behind the cornea

10. Copyright (c) Allyn & Bacon 200410  Anatomy of the Visual System  The Eyes  Lens: Consists of a series of transparent, onion-like layers. Its shape can be changed by contraction of ciliary muscles.  Accommodation:  Changes in the thickness of the lens, accomplished by the ciliary muscles, that focus images of near or distant objects on the retina

11. Copyright (c) Allyn & Bacon 200411  Anatomy of the Visual System  Photoreceptors  Retina:  The neural tissue and photoreceptive cells located on the inner surface of the posterior portion of the eye.  Rod:  Photoreceptor cells of the retina, sensitive the light of low intensity.  Cone:  Photoreceptor cells of the retina; maximally sensitive to one of three different wavelengths of light and hence encodes color vision.

12. Copyright (c) Allyn & Bacon 200412  Anatomy of the Visual System  The Eyes  Fovea:  Area of retina that mediates the most acute vision. Contains only color-sensitive cones.  Optic Disk:  Location on retina where fibers of ganglion cells exit the eye. Responsible for the blind spot.

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14. Copyright (c) Allyn & Bacon 200414  Anatomy of the Visual System  Photoreceptors  Bipolar cell:  A bipolar neuron located in the middle layer of the retina, conveying information from the photoreceptors to the ganglion cells.  Ganglion cell:  A neuron that receives visual information from bipolar cells, its axons give rise to the optic nerve.

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17. Copyright (c) Allyn & Bacon 200417  Anatomy of the Visual System  Photoreceptors  Lamella:  A layer of membrane containing photopigments; found in the rods and cones.  Photopigment:  A protein dye bonded to retinal, a substance derived from vitamin A; responsible for the transduction of visual information.  Opsin:  A class of protein that, together with retinal, constitutes the photopigments

18. Copyright (c) Allyn & Bacon 200418  Anatomy of the Visual System  Photoreceptors  Retinal:  A chemical synthesized from vitamin A, joins with an opsin to form a photopigment  Rhodopsin:  A particular opsin found in rods

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20. Copyright (c) Allyn & Bacon 200420  Anatomy of the Visual System  Connections between Eye and Brain  Dorsal lateral geniculate nucleus:  Cell bodies within the lateral geniculate body of the thalamus; receives inputs from the retina and projects to the primary visual cortex.  Magnocellular layer:  One the inner two layers in the dorsal lateral geniculate nucleus; transmits information necessary for the perception of form, movement, depth, and small differences in brightness to the primary visual cortex.

21. Copyright (c) Allyn & Bacon 200421  Anatomy of the Visual System  Connections between Eye and Brain  Parvocellular layer:  One of the four outer layers of neurons in the dorsal lateral geniculate nucleus; transmits information necessary for perception of color and fine details to the primary visual cortex.

22. Copyright (c) Allyn & Bacon 200422  Coding of Visual Information in the Retina  Coding of Light and Dark  Striate cortex:  The primary visual cortex.  Optic chiasm:  A cross-shaped connection between the optic nerves, located below the base of the brain, just anterior to the pituitary gland.

23. Copyright (c) Allyn & Bacon 200423  Coding of Visual Information in the Retina  Coding of Light and Dark  Calcarine fissure:  Horizontal fissure on the inner surface of the posterior cerebral cortex; the location of the primary visual cortex.

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28. Copyright (c) Allyn & Bacon 200428  Analysis of Visual Information: Role of the Striate Cortex  Anatomy of the Striate cortex  David Hubel and Torsten Wiesel  1960’s at Harvard University  Discovered that neurons in the visual cortex did not simply respond to light; they selectively responded to specific features of the visual world.

29. Copyright (c) Allyn & Bacon 200429  Analysis of Visual Information: Role of the Striate Cortex  Modular Organization of the Striate Cortex:  Striate cortex:  The striate cortex is divided into approximately 2500 modules, each approximately 0.5 X 0.7 mm and containing approximately 150,000 neurons.  Ocular dominance:  The extent to which a particular neuron receives more input from one eye than from the other.

30. Copyright (c) Allyn & Bacon 200430  Analysis of Visual Information: Role of the Visual Association Cortex  Extrastriate cortex:  A region of the visual association cortex; receives fibers from the striate cortex and from the superior colliculi and projects to the inferior temporal cortex.  Regions respond to particular features of visual information such as orientation, movement, spatial frequency, retinal disparity, or color.

31. Copyright (c) Allyn & Bacon 200431  Analysis of Visual Information: Role of the Visual Association Cortex  Perception of Color  Achromatopsia:  Inability to discriminate among different hues; caused by damage to the visual association cortex.  Inferior temporal cortex:  In primates the highest level of the ventral stream of the visual association cortex; located on the inferior portion of the temporal lobe.

32. Copyright (c) Allyn & Bacon 200432  Analysis of Visual Information: Role of the Visual Association Cortex  Analysis of Form  Agnosia:  Inability to perceive or identify an object by means of a particular sensory modality.  Visual agnosia:  Deficits in visual perception in the absence of blindness; caused by brain damage.  Aperceptive visual agnosia:  Failure to perceive objects by their shape, even though visual acuity is relatively normal.

33. Copyright (c) Allyn & Bacon 200433  Analysis of Visual Information: Role of the Visual Association Cortex  Analysis of Form  Prosopagnosia:  Failure to recognize particular people by the sight of their faces.  Associative visual agnosia:  Inability to identify objects that are perceived visually, even though the form of the perceived object can be drawn or matched with similar objects.

34. Copyright (c) Allyn & Bacon 200434  Analysis of Visual Information: Role of the Visual Association Cortex  Perception of Spatial Location  Balint’s syndrome:  A syndrome caused by bilateral damage to the parieto-occipital region; includes optic ataxia, ocular apraxia, and simultanagnosia.  Optic ataxia:  Difficulty in reaching for objects under visual guidance.

35. Copyright (c) Allyn & Bacon 200435  Analysis of Visual Information: Role of the Visual Association Cortex  Perception of Spatial Location  Ocular apraxia:  Difficulty in visual scanning.  Simultanagnosia:  Difficulty in perceiving more than one object at a time.