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Sensory Processes and Perception.docx

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University at Buffalo
PSY 101
Professor Berg

Sensory Processes and Perception Tuesday, February 18, 2014 3:15 PM Sensory Processes and Perception • Perception o Processes that organize and interpret sensory info o 3 stages of perception: • Sensation  Neural impulses in brain are produced when sensory receptors (in fingers, eyes, etc.) are stimulated Sensory processes provide the brain with a link to the world   Experience or awareness of both internal and external conditions is made possible • Perceptual organization  The brain integrates stored info (memories) with incoming info (sense of signal) to form representations of events in the world  Integration is typically non-conscious  Result of integration process is the percept  Activity in brain travels along path of least resistance  Things that we commonly perceive will "pop-out" or remain salient for us when we observe them subsequent times  Ex. "Trailblazer" analogy, creating a path • Identification and recognition  We assign meaning of percepts (typically)  Our brains help us to gather info about the world; integration processes use info to form a representation for meaningful understanding  What is it and what does it do? Psychophysics • How do we measure the intensity of signals in our environment? • What is the relationship between the physical stimulus and the mental experience? • Gustav Fechner o Set of procedures for relating the intensity of a stimulus (measured in physical units) to the magnitude of sensory experience (measured in psychological units) o Researchers use these procedures for comparing the strength of sensations to the strength of stimuli • Absolute threshold o Minimum amount of physical energy that must be present in stimulus to produce a sensory experience at least 50% of the time • Ex. What is the quietest tone that can still be heard from a given distance? o A psychometric function graph shows % of detections at each stimulus intensity level • Difference threshold o Smallest physical difference between 2 stimuli that can still be recognized • Ex. "Is one sound louder than the other?" (Bass) • Sensory adaptation o We are sensitive to environmental changes; when things do not change for awhile, we become accustomed to that sensory input and less sensitive to it (e.g. entering a room with a bad odor; sunlight when you walk outdoors) o Allows for a more rapid reaction to new sources of sensory info • Signal Detection Theory (SDT) o Procedure for separately evaluating sensory processes and decision-making behavior o Tells us whether participants have a bias toward reporting presence or absence of a signal o False alarm rate too high= bias From physical events to mental events • Transduction o Conversion of physical energy (e.g. waves of light, sound, etc.) to neural impulses o All sensory info is converted into identical types of neural impulses, but different areas of the brain handle different sensory domains • Sensory receptors o Detect environmental stimuli o Convert physical form of sensory signal into cellular signal to be processed by nervous system o Signal info. (e.g. size, intensity, shape, distance) is extracted once it reaches nervous system o Waves of light and sound take time to travel o Our experience of reality is always delayed, but not equivalently o Specific types of receptors: • Mechanoreceptors • Thermoreceptors • Chemoreceptors • Photoreceptors Vision • An extremely complex sense; important for mobile creatures • Cannot overstate the evolutionary advantage of having access to a visual representation of the environment • The human eye: o Pupil • The opening of the eye through which light passes o Iris • In order to control the amount of light entering the eyeball at the pupil, the iris constricts (less light) or dilates (more light) o Lens • Light entering the eye is reversed, inverted, and focused onto the back of the eye by the lens • Handles focusing of near and distal vision o Retina • Located at the back of the eye • Contains receptor cells that are sensitive to light; these cells are known as photoreceptors • Organized layers of neurons convert the energy from light waves into neural signals • 2 types of photoreceptors that line the back of the retina:  Rods • 120 million • Sensitivity to light contrasts • Specialized for low-light environments; become more sensitive in darkness  Cones • 7 million • Sensitivity to color contrasts • Specialized for dealing with bright, colorful stimuli • Fovea  Small area near the center of retina  Packed with cones (no rods here)  Sharpest vision (for color and spatial detail) happens here • Blind spot  Region where optic nerve leaves eye; 18degrees off center  No photoreceptors here… Processes in the brain • Half of the fibers from each retina travel along the optic nerve and remain on that side of the brain, while the other half cross over at the optic chiasma • All fibers end up in the primary visual cortex Seeing color • Objects reflect light onto sensory receptors; depending on the wavelength of the light source we may not be able to see it • The electromagnetic spectrum details the range of wavelengths that the visual system can sense • 3 basic dimensions of color experience: o Hue • Qualitative; determined by wavelength o Saturation • Captures purity and vividness; non-diluted have most saturation, muddy or pastels have intermediate, and grays have no saturation o Brightness • Light intensity; white has the most, black has the least •When colors are analyzed along these 3 basic dimensions: o Humans can discriminate 7 million colors o …can only label a fraction of those (Not) seeing color •Color blindness o Total or partial inability to distinguish colors o Hereditary defect on the X chromosome • 8% for males; .5% for females o Typically 3 types of color receptors in human eye (red, green, and blue); this is known as trichromatic theory o Color blindness occurs when one or more of these receptor types are not present or sparse •Retinitis pigmentosa o Chronic; hereditary eye disease o Black pigmentation observed on retina accompanied by gradual degeneration • Microchip tech. allows patients to be sensitive to light; "see shapes" • Connects bi-polar cells in retina to visual cortex Audition •The physics of sound o Sounds occur when vibrations of molecules transmit energy in physical space o Vibrations spread outward from stimulus in the form of sine waves o 2 physical properties of sine waves: • Frequency  # of cycles in a given amount of time • Amplitude  Vertical range of the wave; physical strength Psychological dimensions of sound • Pitch o Highness or lowness of sound as determined by frequency; full range of human sensitivity is 20Hz to 20,000Hz • Loudness o Sounds experienced as loud or soft as determined by amplitu
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