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