Wadsworth, a division of Thomson Learning

Important Definitions Sensation-stimulation of the sensory systems Perception-interpretation of the sensory information Thresholds Absolute-minimum amount of a stimulus that is detectable by an organism Difference-minimum amount of a change in stimulus that is detectable by an organism Weber’s Law-the size of the difference necessary for the organism to notice it is proportional to the size of the initial stimulus Adaptation-gradual decline in sensitivity to prolonged stimulation Subliminal-a stimulus below conscious awareness Supraliminal-a stimulus above conscious awareness

Vision-The Stimulus Light-electromagnetic radiation Amplitude-brightness wavelength-color saturation-richness or purity of the color

Vision-The Anatomy Cornea-transparent covering on the front of the eye Lens-transparent structure that focuses an image on the back of the eye Pupil-the dark part of the center of the eye that regulates the amount of light that enters the eye Iris-the colored muscle of the eye that changes the size of the pupil Retina-neural tissue at the back of the eye that transfers light information into neural signals Blind Spot-the area of the retina where the optic nerve leaves the back of the eye Fovea-central point of focus on the back of the eye

Vision-Fine Anatomy of the Retina Receptors Rods Provide black/white vision located in high concentration in the periphery of the retina nighttime vision with poor acuity Cones Provide color vision located in high concentration around the fovea daytime vision with high acuity Bipolar Cells-Second-layer cells in the retina Ganglion Cells-Third-layer cells in the retina, their axons form the optic nerve.

Vision-The Visual Pathway

Vision-Theories of Color Vision Trichromatic Theory-the eye contains three types of cones capable of differential responding to various wavelengths of light Opponent Process Theory-color perception depends on receptors that make antagonist responses to three pairs of colors

Visual Perception Gestalt Principles Proximity Simplicity Connectedness Closure Continuity Similarity

Visual Perception Depth Perception-The Visual Cliff Binocular Cues-clues about distance based on the differing views of the two eyes Retinal Disparity-the fact that the right and left eyes see slightly different views of the object Accommodation-the degree to which the two eyes must converge to focus on the object Monocular Cues-clues about distance based on the image in either eye Linear Perspective-parallel lines converge in the distance Relative Size-if two objects are the same, the larger one is seen as closer Overlap-the nearer object overlaps the object farther in the distance Texture Gradient-textures are coarser the closer they are

Visual Perception Perceptual Constancies-the ability to experience a constant perception even when what is reflected on the retina changes Color-an object will be perceived as the same color even if the color reflected on the retina changes (ex: when an object is placed in the shade) Size-an object will be perceived as the same size even if the size reflected on the retina changes (ex: a dog running toward you is not seen as growing in size) Shape-an object will be perceived as the same shape even if the shape reflected on the retina changes (ex: a door opening toward you is still perceived as rectangular)

Select Illusions