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Chapter 4

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PSY 205

Chapter 4 • Sensation: stimulation of sense organs • Perception: selection, organization, interpretation of sensory input • Psychophysics: study of how physical stimuli are translated into psychological experience • Agnosia: inability to recognize objects through sight • Gustav Fechner: published pioneering work on psychophysics (German scientist at Leipzig) • Stimulus: any detectable input from the environment • Threshold: dividing point between energy levels that do/do not have a detectable effect • Absolute threshold: specific type of sensory input is the minimum stimulus intensity that an organism can detect • A just noticeable difference: Smallest difference in stimulus intensity a specific sense can detect • Signal detection theory: proposes that the detection of stimuli involves decision processes as well as sensory processes • Hits: detecting signals when they’re present • Misses: failing to detect signals when they’re present • False alarms: detecting signals when they’re not present • Correct rejections: not detecting signals when they’re absent • Subliminal perception: Registration of sensory input without conscious awareness • Sensory adaptation: gradual decline in sensitivity to prolonged stimulation • Amplitude: height. Related to brightness • Wavelength: distance between peaks. Related to hue • Purity: how varied the mix is. Related to saturation • Saturation: relative amount of whiteness in a color • Ultraviolet: shorter wavelengths • Infrared: longer wavelengths • Cornea: front of the eye • Lens: transparent eye structure that focuses the light rays falling on the retina • Accomodation: occurs when curvature of lens adjusts to alter visual focus. • Nearsightedness: close objects are seen clearly but distant objects appear blurry • Farsightedness: distant objects are seen clearly but close objects appear blurry • Pupil: opening in the center of the iris that permits light to pass into the rear chamber of the eye • Iris: colored ring of muscle surrounding the pupil • Retina: neural tissue lining the inside back surface of the eye; absorbs light, processes images, sends visual info to the brain (rods and cones) • Optic disk: hole in the retina where the optic nerve fibers exit the eye • Cones: specialized visual receptors that play a key role in daylight vision +color vision. Provide better visual acuity (sharpness and precise detail) • Fovea: tiny spot in the center of the retina that contains only cones (visual acuity is greatest) • Rods: specialized visual receptors that play a key role in night vision +peripheral vision • Dark adaptation: process which eye becomes more sensitive to light in low illumination • Light adaptation: process whereby the eyes become less sensitive to light in high illumination • Optic nerve: collection of axons from ganglion cells that connect eye with brain • Receptive field: visual cell is the retinal area that when stimulated affected the firing of that cell • Optic chiasm: point at which the optic nerves from the inside half of each eye cross over and then project to the opposite half of the brain • Optic nerve fibers diverge along two pathways, main pathway handles perception of color, form, contrast, and motion, projects into the thalamus • Simple cells: respond best to a line of the correct width, orientated at the correct angle • Complex cells: care about width and orientation • Feature detectors: Neurons that respond selectively very specific features of more complex stimuli • Visual agnosia: inability to recognize objects • Prosopagnosia: inability recognize familiar faces • Subtractive: color mixing works by removing some wavelengths of light, leaving less light than was originally there • Additive color mixing: works by superimposing lights, putting more light in the mixture than exists in any one light by i
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