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Chapter 5

5. Oct 30 -Chapter 5 -Sensation and Perception.docx

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Western University
Psychology 1000
Lynn Jackson

Chapter 5: Sensation and Perception October 19, 2012 HOW DO WE SENSE OUR WORLDS? Key Point: Sensation and Perception are both active and complex processes Sensation our sense organs detection of and responses to external stimulus and transmission of these responses to the brain o basic sensory processes: example of vision & blind-sight eg. Sensory adaptation -- Perception the processing, organization and interpretation of sensory signals; results in an internal representation of the stimulus o Object perception requires construction o Bottom-up and top-down processing Sensory Coding sensory organs translations of stimulis physical properties into neural impulses o Transduction process by which sensory receptors produce neural impulses when they receive physical or chemical stimulation Sense Stimuli Receptors Pathways to the Brain Taste Molecules dissolved in fluid Taste cells in taste buds on thePortions of facial, on the tongue tongue glossopharyngeal, and vagus nerves Smell Molecules dissolved in fluid Sensitive ends of olfactory Olfactory nerve on mucous membranes in neurons in the mucous the nose membranes Touch Pressure on the skin Sensitive ends of touch Trigeminal nerve above neurons in skin the neck, spinal nerves for touch elsewhere Hearing Sound waves Pressure-sensitive hair cells inAuditory nerve cochlea of inner ear Vision Light waves Light-sensitive rods and cones Optic Nerve in retina of eye Qualitative Differences cause difference sensory receptors to respond to qualitative differences by firing in different combinations Quantitative Differences cause sensory receptors to respond to quantitative differences by firing at different rates Course Coding process by which sensory qualities are coded by only a few different types of receptors, each of which responds to a broad range of stimuli Psychophysics a subfield that examines our psychological experiences of different stimuli o It assesses how much physical energy is required for our sense organs to detect a stimulus and how much change is required before that change is noticed Absolute Threshold minimum intensity of stimulation before you experience a sensation or the stimulus intensity is detected above chance; the point at which paticipants correctly detect a stimulus 50% of the times it is presented Difference Threshold the just noticeable difference between two stimuli the minimum amount of change required for a person to detect a difference o Increases as the stimulus becomes more intense Webers Law the just noticeable difference between two stimuli is based on a proportion of the original stimulus rather than on a fixed amount of difference o Formula delta I/I =a constant Signal Detection Theory (SDT) based on the idea that the detection of a faint stimulus requires judgement about its presence or absence o Signal Detection: If signal is present and observer detects it HIT If participant fails to detect signal MISS If participant detects a signal that was not present FALSE ALARM If signal is not present and there is no detection CORRECT REJECTION Response Bias refers to a participants tendency to report detecting the signal in an ambiguous trial. o The participant must be strongly biased against responding and need a great deal of evidence that the signal is present Sensory Systems are tuned to detect environmental changes Sensory Adaptation a decrease in sensitivity to a constant level of stimulation o Eg. People who live near airports no longer take notice of the noises after a while; Dr. Jackson couldnt tell her coat smelled like dogs because she was desensitized to it o how perception and sensation work together WHAT ARE THE BASIC SENSORY PROCESSES? In Taste, Taste Buds Detect Chemicals Only neurons in the sensory organs respond directly to events in the world. The neurons in the brain do not respond to events in the world; they respond only to input from other neurons. Gustation our sense of taste o Purpose: keeps poisons out of our digestive systems while allowing good food in Taste Buds the sensory receptors that transduce taste information o Mostly located on the tongue but are also spread throughout the mouth and throat Every taste experience is composed of a mixture of five basic qualities: sweet, salty, sour, bitter an unami (Japanese for savoury or yummy; recently recognized as the fifth taste sensation) MSG monosodium glutamate The entire taste experience occurs not in your mouth but in your brain which integrates various sensory signals Supertasters are highly aware of flavours and textures and are more likely to feel pain when eating spicy foods o Have nearly six times the amount of taste buds as normal tasters The same food can taste different because the sensation associated with that food differs in different peoples mouths cultural factors also influence taste preferences Cultural influences begin in the womb In Smell, the Nasal Cavity Gathers Odorants Humans sense of smell is vastly inferior to that of many animals Olfaction the most direct route to the brain o like taste, it involves the sensing of chemicals that come from the outside of the body (odorants) o We smell something when chemical particles or odorants, pass into the nose, and when we sniff, into the nasal cavitys upper and back portions o In the nose and the nasal cavity, the odorants come into contact with the.. Olfactory epithelium a thin layer of tissue within the nasal cavity embedded with smell receptors o These receptors transmit information to the. Olfactory Bulb the brain centre for smell, located below the frontal lobes o from here, smell information goes directly to other brain areas Unlike other sensory information, smell signals bypass the thalamus, the early relay station Prefrontal cortex processes information about whether a smell is pleasant or aversive o Amygdala processes the smells intensity In Touch, Sensors in the Skin Detect Pressure, Temperature, and Pain Haptic Sense the sense of touch o Conveys sensations of temperature, of pressure, and of pain, and a sense of where our limbs are in space Anything that makes contact with our skin provides tactile stimulation, which gives rise to an integrated experience of touch Haptic receptors for both temperature and pressure are sensory neurons that terminate the skins outer layer Pain receptors are found throughout the body, not just in the skin Like other sensory experiences, the actual experience of pain is created by the brain o IE. Phantom Limb Pain ---the person really feels pain, but the pain occurs because the brain misinterprets neural activity Nerve fibres that convey pain information are thinner than those for temperature and for pressure and are found in all body tissues that sense pain: skin, muscles, membranes around both bones and joints, organs and so on. o Two kinds of nerve fibres for pain: fast fibres for sharp, immediate pain and slow fibers for chronic, dull pain, Distinction between thew3 fibres is the myelination or non-myelination of their axons, which travel from the pain receptors to the spinal cord Myelinated axons, like heavily insulated wire, can respond quickly; non-myelinated axons respond more slowly Gale Control Theory (of pain) --states that for us to experience pain, pain receptors must be activated and a neural gate in the spinal cord must allow the signals through to the brain o The brain regulates the experience of pain, sometimes producing it, sometimes suppressing it o According to this theory, pain signals are transmitted by small-diameter nerve fibres, which can be blocked at the level of the spinal cord by the firing of larger sensory nerve fibres Thus sensory nerve fibres can close a gate and prevent or reduve the perception of pain o Because pain is processes in the same areas of the brain as stress, fear and anxiety, it is a sensory experience and an emotional response One area responds to the sensory input from the part of the body that is in pain The other part of the brain that is involved when we feel pain registers the emotional aspect of pain, which includes how unpleasant it is General anaesthesia slows down the firing of neurons throughout the nervous system, and the
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