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Psyc100-Ch5 - Sensation Perception.docx

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PSYC 100
Jaime Palmer- Hague

Psychology 100 Chapter 5: Sensation and Perception Sensation to Perception (p.127) Sensation :  Stimulus-detection process  Receive and translate environmental stimuli into nerve impulses Perception :  Making sense of what the senses tell us (processing and interpretation)  Giving meaning to the sensory information Steps: 1. Stimulus is received by sensory receptors. 2. Transduction: Receptors translate stimulus into nerve impulses. 3. Feature detectors analyze stimulus features. 4. Stimulus features are reconstructed into neural representation. 5. Neural representation is compared with previously stored information in brain. 6. Matching process results in recognition and interpretation of stimulus. Sensory sensitivity (p.128): Absolute Threshold: (limits of stimulus detectability)  lowest intensity at which a stimulus can be detected 50% of the time  The lower the threshold, the greater the sensitivity.  Variations among species (eg dogs) Individual variation in detection: Decision criterion: how certain one must be that a stimulus is present before they will say they detect it  Will change from time to time depending on hunger, expectation (horror movie), etc Signal detection theory: factors that influence decisions about whether or not a stimulus is present  Typical signal detection experiments: see p.128 Hit/Miss/False alarm/Correct rejection  Personalities eg conservative people always say no  Manipulation with cost/reward Subliminal Stimulus: stimulus so weak/brief that although it is received by the senses, it cannot be perceived consciously (consumer experiment p.129) Differences threshold: (ability to discriminate between stimuli)  the “just noticeable difference” that people can perceive 50% of the time.  Weber’s law: jnd is proportional to the intensity of original stimulus (eg weight is 1/50)  Smaller the fraction, greater the sensitivity to differences. Humans: better vision(1/60) than smell(1/4) Sensory Adaptation: diminishing sensitivity to an unchanging stimulus  eg background sound disappearing, cold water only cold at first  Frees senses from constant stuff and allowing them to pick up informative changes that could help survival V ISION : VISUAL SYSTEM Electromagnetic energy/Light waves – stimulus for vision, measured in nanometers (nm) The human eye (p.132)  Waves enter through cornea: transparent protective structure at the front of eye  Behind is pupil: can dilate or constrict to control the amount of light that enters  Pupil’s size is controlled by muscles in the colored iris o Dark room – pupil dilate (bigger) so more light can enter to improve optical clarity o Bright room- pupil constrict (smaller)  Behind pupil is lens: elastic structure that becomes thinner(far)/ thicker (near) to focus on objects  Lens projects a image onto the retina: a multilayered light-sensitive tissue at the rear of the fluid-filled eyeball  The lens reverses the image but the brain reverses the visual input into the image we perceive  Ability to see clearly depends on len’s ability to focus. o Myopia – nearsightedness (cant see far), lens focuses the image before the retina o Hyperopia – farsightedness (cant see near) lens does not thicken enough and image is there before focused on a point behind the retina Photoreceptors (p.133): The retina contains two types of receptor cells (in retina): Rods :  120 million  black and white receptors  best in dim light  500 more times more sensitive to light than cones, but don’t react to color sensations  Found mostly throughout retina Cones  6 million  Color receptors  function best in bright illumination  found mostly in fovea: center of retina with no rods. Cones decrease in concentration the farther away they are from fovea.  How rods and cones send their message to the brain: Light > rods and cones have synaptic connections with bipolar cells > synapse with ganglion cells > Optic nerve: bundle of ganglion cells axons > to brain. Dark adaptation : gradual regeneration of photopigments that have been depleted by brighter illumination. Cones adapt in 10 mins, rods continue to increase sensitivity for another 20 mins. Color-Deficient Vision (p.137)  Trichromats: normal color vision, can see all 3 systems: blue-yellow, red-green, black-white  Dichromat: blind in one system (B-Y or R-G)  Monochormat: can only see B-W, total color-blind. Analysis and Reconstruction of visual senses (p.138) Feature detectors: cells fire selectively in response to visual stimuli that have specific characteristics  Eg celebrities, faces in arts, shapes, movements, etc. / + \ + — = A  Discovered by Hubel & Wiesel  Visual stimuli are analyzed by features detectors in the primary visual cortex, and the stimulus elements are reconstructed and interpreted in visual association cortex. A UDITION : SOUND SYSTEM Sound waves – stimuli for hearing. Receptors are hair cells in organ of Corti of the inner ear. Frequency: the number of sound waves (cycles) per second, how rapidly air vibrates  Measured in hertz (Hz) – 1Hz is 1 cycle per second  Related to pitch. Higher frequency/hz, the higher the pitch Amplitude: the vertical size of sound waves – amount of compression and expansion  Measured in decibels (dB) – measure of physical pressures that occur at the eardrum  Related to loudness. Absolute threshold for hearing is 0db, increase of 10db represents a tenfold increase in loudness. 140db+ can cause potential damage to auditory system Timbre?  Quality of a sound  Complexity of a sound wave The Ear (p.141)  Sound waves travel into auditory canal leading to the eardrum: a membrane that vibrates in response to sound  Beyond is middle ear (ossicles) with three tiny bones: hammer (malleus), anvil (incus) and stirrup (stapes)  First bone (hammer) is attached to eardrum, third (stirrup) is attached to another membrance.  The oval window is the boundary between middle and inner ear  Inner ear contains the cochlea: coiled snail-shaped tube about 3.5cm and is filled with fluids and contains the basilar membrane: membrane that runs the length of the cochlea  Inside BM is organ of Corti: contains thousands of tiny hair cells that are sound receptors  Tip of hair cells are attached to another membrane, the tectorial membrane.  The hair cells synapse with neurons of the auditory nerve, send impulses to auditory cortex Auditory Transduction: from pressure waves to nerve impulses  When sound waves strike eardrum, pressure created at oval window by 3bones of middle ear sets fluid inside cochlea into motion. The fluid waves vibrate the basilar membrane and the tectorial membrane, causing a bending of hair cells in the organ of Corti. The bending of hair cells triggers the release of neurotransmitters to neurons of auditory nerve and sent impulse to brain.  Within auditory cortex are feature-detector neurons that respond to specific kinds of auditory input. Hearing loss (p.143) Conduction deafness: problem with structure of ear that transmit vibrations to the cochlea  Punctured eardrum or bones not functioning in middle ear -- Can be fixed with hearing aid. Nerve deafness: damaged receptors within inner ear or damage to auditory nerve  Aging, disease or exposure to loud sounds G USTATION : GUSTATORY SYSTEM – SENSE OF SMELL ( P .144)  Sensitive to chemical molecules rather than some form of energy. Five basic taste: sweet, sour, salty, bitter, umami  Also have tactile (touch/texture) and temperature receptors Taste buds: chemical receptors concentrated along the tip, edge and back of tongue  Each taste bud is most responsive to one or two of the basic taste qualities but responds weakly to the others as well  Umami: increase the intensity of other taste qualities. (MSG)  Humans have 500-10,000 buds, each consisting several receptor cells arranged like segments of orange  When substance enters mouth, it interacts with saliva to form a chemical solution that flows into the taste pore and stimulates the receptor cells. Taste results from complex patters of neural activity produced by four types of taste receptors.  Genetic differences in ‘taste’.  Also culture and learning Sense of taste can also discriminate between nutrients and toxins.  Response to some taste qualities is innate. o Eg newborn respond positively to sugar water and negatively to bitter substances  Most poisonous substances are bitter and this emotional response have hardwired into our physiology  High calorie foods are mostly sugar-rich  Most humans do not live in food-scarce environment anymore so preference for sweet substances evolved and tend to over consume sweet foods  There are genetic differences in taste responses  Supertasters (25% of Americans): o find broccoli, caffeine, and saccharin unpleasantly bitter, high sensitivity to sweet,salty, and spicy o Have more taste buds! O LFACTION : OLFACTORY SYSTEM – SENSE OF SMELL (P .144)  Receptor are long cells in upper nasal cavity  Humans have 40 million olfactory receptors, dogs have 1 billion  Olfactory receptors resemble neurotransmitter binding sites on neurons (lock and key)  The receptors send input to the olfactory bulb: a forebrain structure above nasal cavity Phe
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