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Vision. Marisa Badamo , Shelly Elango , Mindy Heard, Carly Niedbalski, and Arif Syed. Vision: How the Nervous System Processes Light. Good vision helps us detect desired targets, threats, and changes in our physical environment and to adapt our behavior accordingly .
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Vision Marisa Badamo, Shelly Elango, Mindy Heard, Carly Niedbalski, and Arif Syed
Vision: How the Nervous System Processes Light • Good vision helps us detect desired targets, threats, and changes in our physical environment and to adapt our behavior accordingly
The Anatomy of Visual Sensation • The eye gathers light, focuses it, converts it to neural signals, and sends these for processing into a visual image • The eye extracts information from light waves and transduces them into neural signal the brain can process • The transduction happens in the retina • Retina: The thin, light sensitive layer at the back of the eyeball • Retinal Disparity: The slight difference in the two retinal images due to the angle from which the eye views an object • Acuity: acuteness and clearness of the vision
Photoreceptors are light sensitive cells that contain rods and cones • Rods and cones are specialized neurons that absorb light and create neural impulses • Rods detect low intensities of light at night but cannot distinguish color • Cones are specialized to detect the light waves we sense as red, blues, or green. Not sensitive to light • Accommodation: process by which the eye changes optical power to maintain a clear image when an object’s distance varies
Adaptation: ability of the eye to adjust to various levels of darkness and light • Cones are concentrated in the foveawhich is where we have the sharpest vision • Bipolar cells collect impulses from photoreceptors and send them to ganglion cells • The axons of the ganglion cells form the optic nervewhich sends information from the eye to the brain
The blind spot is a gap in the visual field resulting from the point at which the optic nerve exits the eye • The visual cortex is where the brain transforms neural impulses into visual sensations of color, form, boundary, and movement • Nearsightedness: the ability to see near things more clearly than distant ones • Farsightedness: seeing or able to see to a great distant • Parallel processing: the ability of the cortex to perform more than one task at one time
How the Visual System Creates Color • Color: also called hue. Color is not a property of things in the external world. It is only a psychological sensation created in the brain from information obtained by the eyes from the wavelengths of visible light. • Color does not exist outside the brain, but only in the mind of the viewer
Color is created when the wavelength in a beam of light is recoded by the photoreceptors in the form of neural impulses and sent to specialized areas of the brain for sensory processing. • Amplitude: the physical strength of the wave. Measurement from the top (peak) to the bottom (valley) of the graph of a wave • Wavelength: the distance electromagnetic energy waves travel making one wave cycle
The eyes detect a special form of energy called visible light (pure energy) • Visible light lies on the electromagnetic spectrum: the entire range of electromagnetic energy, including radio waves, X-rays, microwaves, and of course visible light • Visible spectrum: the tiny part of the electromagnetic spectrum to which our eyes are sensitive.
Within the visible spectrum light waves of different lengths give rise to different colors • Longer waves: red • Medium waves: yellow and green • Small waves: blue • The wavelengths of light that the eye obtains the information is used by the brain to construct colors • Visual experiences of color, form, position, and depth are all based on processing the same stream of sensory information in different parts of the visual cortex
Two Ways of Sensing Colors • Color processing begins in the retina • Trichromatic theory(Young-Helmholtz Theory): the idea that colors are sensed by three different types of cones sensitive to light in the red, blue, and green wavelengths. Explains the earliest stage of color sensation • Opponent-process theory: the idea that cells in the visual system process colors in complementary pairs, such as red or green. Explains color sensation from the bipolar cells onward in the visual system • Explains some cases of blindness • Afterimages: sensations that linger after the stimulus is removed. Most are negative which appear in reversed colors.
Saturation: How intense a color is determined by a combination of light intensity and how much it is distributed across the spectrum of different wavelengths • Monocular cue: depth perception cue that requires information from one eye • Binocular cue: depth perception cue that requires information from both eyes
Color Blindness • Color blindness: typically a genetic disorder that prevents an individual from discriminating certain colors. The most common form is red-green color blindness. • Monochromats- complete color blindness total inability to see distinguish color • Those who confuse yellow and blue are very rare • Only about 500 cases involve people seeing no color at all
