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Chapter 5

Chapter 5- Sensation.doc

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Steve Joordens

Chapter 5 SensationEverything we learn is detected by sense organs and transmitted to our brains by sensory nervesoWithout sensory input out brain would learn nothing thing no thoughts and have no experienceThe sense organs and the sensory nerves have evolved to provide us with useful info about the external worldSensory ProcessingSensation the detection of the elementary properties of a stimulus Ex brightness colour warmth etcPerception the detection of the more complex properties of a stimulus Ex location movements backgrounds etcThe detection of objects both animate and inanimateTransductionSense organs detect stimuli provided by light sound odour taste or mechanical contact with the environmentTransduction the conversion of physical stimuli into changes in the activity of receptor cells of sensory organsThe sense organs convert energy from environmental events into neural activityReceptor cell a neuron that directly responds to a physical stimulus Ex light vibrations or aromatic moleculesThey release neurotransmitters that stimulate other neurons so altering the rate of tiring of their axonsSensory CodingNerves are bundles of axons each of which can transmit action potentials and they cannot be alteredoDifferent stimuli cannot be translated into different types of actions potentials yet we can detect an enormous number of different stimuli with each of our sense organsCode a system of symbols or signals representing info Ex spoken English and traffic lightsIf we know the rules of a code we can convert a message from one medium to another without losing any infoAnatomical Coding1Anatomical coding different features are coded by the activity of different neuronsSensory coding for the body surface is anatomicalThe firing of a particular set of neurons tells where the body is being touchedPrimary somatosensory cortex contains a neural map of the skin and receptors in the skin in different parts of the body send info to different parts of the primary somatosensory cortexTemporal CodingTemporal coding different features are coded by the pattern of activity of neuronsBy firing at a faster or slower rate according to the intensity of a stimulus an axon can communicate quantitative info to the brainThe rate at which these neurons fire tells how intense that touch isPsychophysicsPsychophysicsa branch of psychology that measures the quantitative relation between physical stimuli and perceptual experience the physics of the mindThe Principle of the JustNoticeable DifferencesJustnoticeable differencedifference threshold jndthe smallest difference between 2 similar stimuli that can be distinguishedErnst Weber usedthis methodEx when participants were asked to hold 2 weights and say whether the weights felt different in weight they say that the weights are the same because they could barely distinguish a 40g weight to a 41g weight ratio is 1 in 40Gustav Fechner assumed that the jnd was the basic unit of a sensory experience so he measured the absolute magnitude of a sensation in jndsoHis greatest contribution to psychology was to show how a logarithmic function could be derived from Webers principleWeber fraction the ratio between a justnoticeable difference and the magnitude of a stimulusReasonably constant over the middle range of most stimulus intensitiesSS Stevens suggested a power function to relate physical intensity to the magnitude of sensationbS klSignal Detection TheoryS the psychological magnitude of the sensationl the intensity of the physical 2stimulus
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