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Chapter 5

Chapter 5_Sensation[1].doc

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Dan Dolderman

Chapter 5 Sensation, perception, and attention Perception is our bridge with the world  In order to perceive, we rely on our sense organs-eyes, ear, skin, nose, tongue  We are only sensitive to limited stimuli Ways we experience the world into 2 phases: sensation and perception  Sensation: how our sense organs respond to and detect external stimulus energy, and how those responses are transmitted to the brain  detection  Perception: brain’s further processing of these signals that ultimately results in an internal representation of stimuli and conscious experience of the world  Construction of useful and meaningful info about the environment Eg. Green light emits photo sensed by eye and tra(smit s(gnal to brain sensation Brain processes neural signals and observer experiences a green light (perception) Study of bodily systems that convert stimulus energy into useful info How do we sense our worlds?  Evolved through time Stimuli must be coded to be understood by the brain  Sensory coding  Different physical environment coded by diff patterns of neural impulses  Receptors are specialized neurons in the sense organ that pass impulses to connecting neurons when they receive phy or chemical stimulation- TRANSDUCTION  Transmit info to brain in form of neural impulse  Sensory info must go through thalamus then send info to cortex interpreted as sight, smell, sound, touch, taste  Sensory code divided into 2 categories: quantitative and qualitative  Intensity, brightness… determined by firing frequency  Colour, taste  Different receptors types for different stimulus  In most sensory systems, except smell, receptors provide coarse coding, coded by only a few receptors responding to many stimuli Psychophysics relates stimulus to response  Psych and physical stimuli  Developed by Gustav Fechner: how much physical energy needed for us to sense Sensory thresholds:  Absolute threshold: min intensity of stimulation before we can experience a sensation  Eg. Faintest sound we can hear  Difference threshold: noticeable difference between two stimuli  Min amount of change required for us to detect a difference  Weber’s law: the size of a noticeable diff is based on a relative proportion of difference rather than a fixed amount of difference  Eg. 96/100 and 6/10  Signal detection theory:  Flaw to absolute threshold, forgot to account for human judgment  Detecting stimulus requires making judgment about its presence or absence, based on a subjective interpretation of ambiguous info  Trials to judge whether stimulus was present or not  Hit (y/y), miss(y/n), false alarm (n/y), correct rejection (n/n)  Response bias refers to participant’s tendency to report detecting the stimulus on ambiguous trials  Eg. Doctor may tend to say abnormality because treatment doesn’t harm patients  Compare hit vs. false alarm Sensory Adaptation  Sensitivity to stimuli decreases over time  Tuned to detect changes in environment, less critical to keep responding to unchanging stimuli  Eg. Construction noise while reading What are the basic sensory processes?  Taste, smell, touch, hear, vision In gustation, taste buds are chemical detectors  Taste receptor are taste buds of tongue and mouth  Microvilli at tip of tongue contact with saliva, stimulate signal to brainstem region called medulla and to thalamus and cortex, produce experience of taste  Taste receptors: sweet, sour, salty, bitter  Diff taste buds are spread uniformly throughout tongue and mouth  Taste relies heavily on sense of smell, texture,  Taste experience occurs in brain  Integration of sensory signals that gives us the experience of taste  Intense taste s(nsation supertaster-6 times taste buds as normal taster  They’re picky eaters, because some taste seem overwhelming  More sensation isn’t always better In smell, the nasal cavity gathers particles of odour  Sensing chemical from outside body  Contact with olfactory epithelium embedded with olfactory receptor  Trigger chemical receptor and nerve impulses convey info to olfactory bulb  Brain center for smell, below frontal lobes  Smell bypass thalamus directly to brain areas  Prefrontal cortex process info about whether a smell is pleasant or aversive  Amygdala process intensity of smell  Thousands of diff receptors in olfactory epithelium, responsive to diff chem. Group  How receptor recognize odour not known: specific smell, or by amt of receptor activated  Animals have stronger olfactory capabilities because we rely on more vision and other senses  Smell evoke moods eg. Mouthwash  Pheromones recognized by specialized receptors in nasal cavity behavioural reaction in animals, sexual signaling in animals and humans, menstrual cycle synchronization In touch, sensor in the skin detect pressure, temp and pain  Haptic sense  Tactile stimulation with skin  Haptic receptors are sensory neurons that terminate in the outer layer of skin  Long axons enter cns by spinal or cranial nerves  Receptor at base of hair follicles, capsules in skin  Separate receptor for hot and cold  Why can’t tickle yourself: brain areas involved in touch sensation respond less to self produced tactile stimulation than to external tactile stimulation Two types of pain  Warning system  Genetic disorder in children insensitive to pain usually die young  Actual experience of pain created by brain  Eg. Amputated limb feel phantom pain in nonexistent limb because of misinterpretation of neural activity  Damage skin activate haptic receptor  Nerve fibers that convey pain are thinner than others, found in all body tissue that sense pain  Fast and slow fiber  Fast pain receptor activated by strong physical pressure and temp extremes  Slow acting receptor activated by chemical change in tissue when skin is damaged  Fast pain allows recoil, slow pain allows keep away from using affected part Gate control theory  By Ronald melzack  In order for us to experience pain, pain receptors must be activated and a neural gate in spinal cord must allow these signals through to the brain  Close gate by stimulating other haptic receptor eg. Scratching itch satisfying  Overwhelms signals from pain receptor and reduce itch  Cognitive state can close gate, distraction  One region of midbrain influences wheter gate is open or shut  Endorphins block pain, act on midbrain region In hearing, ear is a sound wave dectector  Stimulus is the displacement of air molecues caused y changes in air pressure-sound wave  Amplitude determine loudness  Frequency determines pitch  20hz to 20000hz  what you hear occur in brain as it integrates the different signals provided by various sound waves  no sound unless registered in brain  tree banging unless someone there to hear it  air pressure produce sound wave arrive at outer ear and travel down auditory canal to eardrum marking beginning of middle ear  ear drum vibrate and transfereed to 3 tiny bones called ossicles: hammer,anvil, stirrup  transfer vibration to eardrum to oval window, membrane of cochlea (inner ear, fluid filled tube curls into snail like shape)  curls into snail like shape and ossicles amplify vibrations  thru center of cochlea is thin basilarmembrane  vibration of oval window create waves in fluid of inner ear and stimulate hair cell of basilar membrane, generate action potential. Converted into neural signal travel to auditory nerve to brain  when wave hit fluid of inner ear, fluid causes basilar membrane to move up and down, activating electrical potentials in hair cells Time and place coding for pitch  temporal coding used to encode low frequencies  1000hz tone cause hair cell to fire 1000times/sec  up to 4000 hz  place coding  diff receptors in basilar membrane respond to diff frequencies  diff frequencies activate receptors at diff locations on basilar membrane  same receptors, different locations  hair cells at base of cochlea activated by high freq, at tip are low freq sound Concurrent processing to locate sounds  sensory receptors do not code location  difference in timing between arrival of sound and intensity at each ear to locate sound In vision, the eye detects light waves  brain involvement again  very little of what we see takes place in eye, but rather from active constructive processes that occur throughout much of brain to produce visual experiences  cascade of neural processes  light pass through cornea (outer layer of eye), focuses light by refraction  light enter and bent inward by lens focues light to form image on retina (inner surface of eyeball)  more refraction, lens is adjustable  pupil contract or dilate to alter how much enters eye  iris control size of pupil and give eye colour  muscles change shape of lens flatten to focus distant objects, thickening to focus closer object (accommodation)  inverted image on retina rods and cones  retina has two types of receptor cells: rods and cones  rods respond at low levels of illumination for night vision  not support colour vision  can’t resolve fine details  cones are for vision under light, for colour and detail  chemicals called photopigments w/I rods and cones initiate transduction of light waves into electrical neural impulses  120 million rods and 6 million cones in each retina  cones near center of retina called fovea  cones spread out  rods on edges of retina, none in fovea transmission from eye to brain  retina is part of brain visible from outside the skull  light transduced into neural impulses by rods and cones  other cells in retina help visual system process incoming info  cells in middle layer transduce neural impulse from synapse with ganglion cells which in turn transmit neural impulse to brain receptive field is region of visual space to which neurons in primay visual cortex are sensitie  located on region of retina  ganglion cells have receptive fields making them sensitive to edges, insensitive to unifor regions lateral inhibition  Hermann grid  Receptor coding info from white lines are inhibited by their neighbors on two sides or four sides, making black dots  Brighter against dark background-simultaneous contrast  Visual system sensitive to edge and contours Colour determined by wavelength  Brightness vs. lightness  Lightness refer to brightness relative to its surrounding (psych dimension)  Saturation: purity of colour Subtractive colour mixing  Short wavelength (ie blue) absorbs long wavelength and reflect short wavelength  Subtractive primary colours: blue, red, yellow Additive colour mixing  Green, red, blue Explaining
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