PSY 201 1st Edition Lecture 8Outline of Last Lecture I. Vision (continued from last lecture)a. Coding of contrast and contour (based on pdf reading on Blackboard)b. Generalizations about processing in visual systemi. Feature detectionii. Functional specializationOutline of Current LectureI. Three perceptual dimensions of colorII. Color and wavelengthIII. Color mixing: additive and subtractiveIV. Two theories of color visiona. Trichromatic theoryb. Opponent process theoryV. PsychophysicsVI. Perceptual OrganizationCurrent LectureI. Color vision: the ability to discriminate between different wavelengths of light when no brightness cues are presenta. Color=psychological construct; stimuli have different wavelengths that are reflected, but those wavelengths don’t have any hueII. Physical vs. perceptual attributes of visual stimulia. Wavelength: shorter wavelength can dictate colorb. Amplitude: height of the wave dictates the brightnessc. Purity: number of types of wavelengths dictates the saturation of the color (moretypes mean greater saturation)III. Color and wavelengtha. Experience of color depends on which wavelengths hit the eyei. Light and color:1. Directly from light sources (TV, light bulbs, sun)2. Light bouncing off (reflected from surfaces)IV. Color mixinga. Mixing pigments means subtractive color mixingThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. When two pigments are mixed, only the wavelengths that are absorbed by neither pigment (reflected by both) will be seenii. Each pigment is subtracting wavelengths outiii.b. Additive color mixing: when colored lights are mixed instead of pigmentsi. By increasing the intensity of lights, you can create white lightV. Two theories of color visiona. Psychophysical results used to propose two mechanismsi. Trichromatic theory: three primaries law of color1. Color matching experiments with lighta. Select three different wavelengths and match the color of any wavelength by mixing them in various proportionsi. Ex: yellow (100% intensity)= red (50%)+green (50%)+blue (0%)ii. Three colors span the entire color spectrum, and changing their intensities allows to change the color because it changes the responsiveness of the cones (in different ratios depending on the color)2. Hypothesis: color vision depends on three-receptor mechanism (with different sensitivities)a. Light of a wavelength will stimulate the three receptors in a unique wayb. Each wavelength ii. Opponent-process theory: explain perceptual phenomena in which colorsseemed to be paired as opposites1. Opposing afterimagesa. Red: green afterimageb. Yellow: blue afterimage 2. Visualizing colors: easy to visualize color combinations (turquoise, orange), but impossible to think of others (reddish- green, bluish-yellow)3. Hypothesis: color vision based on three mechanisms responding in opposition to light intensities or wavelengths:a. Black-whiteb. Red-greenc. Blue-yellow4. Function of opponent cells: enhance ability to distinguish betweendifferent wavelengthsVI. Psychophysicsa. Study of relationships between physical stimuli and psychological responsesi. One of the earliest psychologists: structuralists (how dim of a light can be perceived?)ii. Detection1. Absolute threshold: smallest amount of stimulus energy that is able to be detected (faintest detectable stimulus)a. Subthreshold<threshold<suprathresholdb. Intensity of a stimulus that is sufficient for detection 50% of the timec. Conducted experiments for all types of sensesiii. Discrimination1. Difference threshold: smallest difference in stimulus energy that can be discriminated between the stimuli presented (just-noticeable difference; JND)a. Present standard stimulus (always same intensity) and a comparison stimulus (different intensities)b. Size of a difference that can be detected 50% of the timei. JND is smaller for less intense standard stimuli and larger for more intense standard stimuliVII. Perceptual organizationa. Gestalt psychologyi. Describes various ways the perceptual system organizes elements into wholesii. Reaction against structuralists1. Visual system actively organizes world into objects rather than justregistering the brightness and color of stimulia. ‘Whole is greater than the sum of its parts’ (phi phenomenon)iii. Figure ground: automatic tendency to see some parts of a scene as objects and others as the background1. Figure: parts that stand out, sharply delineated, distinct shapesa. Usually smaller and surrounded, located in the frontb. Has contours2. Ground: usually the larger field, extends behind the figureiv. Grouping principles: rules that dictate how we perceive shapes and forms1. Proximity: tendency to see stimulus elements by closeness2. Similarity: elements that are similar get grouped together visually3. Closure: we supply missing elements to complete the figure4. Good continuation: see elements in ways that produce continuouslines without change in direction5. Common movement/fate: elements moving in the same direction at same rate, you organize the elements into one object6. Good form/simplicity: perception strives for simplest interpretationb. 3-D Depth perceptioni. Vision registers the spatial arrangement of objects and surfacesii. 2-D array of light has cues for depth and distance1. Ex: sidewalk art, 2-D pictures made to look 3-Diii. Going from 2-D retinal image to 3-D isn’t always straightforward1. Different 3-D image can respond to different retinal