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Psychology & Brain Sciences

Sensation  Stage #1: Sensation o The processes of: a) converting the physical world into a mental representation (transduction) b) relaying that information to the brain (conduction)  Example: variations of light  experience of color / variations of air pressure  experience of sound  Stage #2: Perception o The processes by which we: select, organize and interpret these mental representations  Example: we can recognize the color green / we can distinguish Bach from Britney Spears  Psychopsychics: the study of the relationship between physical characteristics of stimuli (energy)  and our psychological experience of them o Example: light  brightness / sound -> volume / pressure  weight / taste  sweetness  Absolute thresholds: smallest magnitude of a stimulus that can be reliably discriminated from NO stimulus at least 50% of the time  Difference thresholds: minimum difference between two stimuli that a person can detect at least 50% of the time o Just noticeable difference  Signal detection theory o Predicts how and when we will detect the presence of a stimulus amidst background stimulation o Complex decision mechanisms are involved to determine if a stimulus exists  Based on both: 1. Stimulus strength 2. Our experiences: expectations, motivation, level of fatigue a. Sounds in my house  Point: absolute thresholds and just noticeable differences are not fixed o Our sensitivity to a stimulus varies based on experiences  Factors that affect absolute and difference thresholds: 1. Chance variation – noise in the system influences sensitivity 2. Stimulus intensity – Weber’s law: the greater the intensity of a stimulus, the larger the difference mist be to detect a difference a. They must differ by a constant proportion 3. Sensory adaptation – our sensitivity to an unchanging stimulus diminishes Question: how do we turn light energy into vision (psychological experiences)? 2 aspects of light energy – light wave are crucial: Wavelength: the distance between peaks of the light wave. Corresponds to our sensation of color ROYGBIV  short wavelength (violets/blues) long wavelenths (reds/oranges) Amplitude: the intensity of the light wave. Corresponds to our sensation of brightness Small amplitude  dull color / great amplitude  bright color Vision Rods: cells in the periphery of the retina sensitive to light Cones: cells in the center of the retina (fovea) sensitive to focus and color perception Theories of color vision: 1. Trichromatic theory (young-hemholtz) a. Any color can be created by combining the red, green and blue light in varying combinations In our eyes we have three kinds of cones: Cone one: maximally sensitive to blue Cone two: maximally sensitive to green Cone three: maximally sensitive to red - Our experiences of colors results from mixing different levels of response from these three cone types 2. Opponent process theory a. Opposing retinal processes enable color vision b. Natural impulses are antagonistic, a stimulus that elicits a response from the “red”, depresses a response of green Hearing Question: how we do turn variations in air pressure (physical stimulus – sounds waves) into our sense of hearing (psychological experience)? Two aspects: 1. frequency a. the number of complete cycles per unit time (hertz-cycles per second) b. corresponds to our psychological sensation of pitch 2. Amplitude a. The intensity of the waves b. Corresponds to our psychological sensation of volume  Perceiving pitch: (highs vs. low sounds) o Place theory – different pitches produce responses on different places on the basilar membrane o Works well with high pitched sounds o Frequency theory – different pitches cause the basilar membrane, itself, to vibrate at different frequencies o Works well with low-pitched sounds  Perceiving volume: (loud vs. soft sounds) o Not movement of B
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