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Chapter 5

chapter 5

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Ingrid L.Stefanovic

CHAPTER 5- SENSATION SENSORY PROCESSESING Sensation (simple sensation): detection of elementarysimple properties of stimuli (brightness, colour, warmth, sweetness) Perception (complex perception): detection of objections (both animate& inanimate), their locations, mvments, & background nature that involves learning Example: seeing red colour = sensation Seeing red apple= perception Belief: perceptions depend on learning VS sensation involves innate prewired physiological mechanisms TRANSDUCTION Transduction: conversion of physical stimuli into changes in the activity of receptor cells of sensory organs Convert energy from environmental events into neural activity; through receptor cells or somatosenses Each sense organ responds to a particular form of energy from environment + translate the energy into neural firing for the brain to respond In most senses, Receptor cells neuron that directly responds to physical stimulus (light, vibration, aromatic molecules)== release chemical transmitter substances that stimulate other neurons, which alters the rate of firing in their axons Other senses such as somatosenses (body senses) doesnt require receptor cells, the dendrites of neurons respond directly to physical stimuli wo receptor cells **in order for us to know whats going on in the outside; specific actions are required in order to see & understand the outside world. This info is gathered by sense organs located outside the brain Task of sense organ: transmit single to brain then the brain does it job to analyze the info and reconstruct what occurred Sense organs detect stimuli (light, sound, odour, taste) stimuli info transmit to brain through neural impulses axn potential TYPES OF TRANSDUCTIO BY SENSE ORGANS LOCATION OF SENSE ORGAN ENVIORNMENTAL STIMULI ENERGY TRANSUDCTED Eye Light Radiant energy Ear Sound Mechanical energy Vestibular system Tilt rotation of head Mechanical energy Tongue Taste Recognition of molecular shape Nose Odour Recognition of molecular shape Skin, internal organs Touch Mechanical energy Temperature Thermal energy vibration Mechanical energy Muscle Pain Chemical rxn Stretch Mechanical energy SENSORY CODING Because axn potentials and the duration cannot be changed, codes must be used to transmit specific info to the brain (example: how do sense organs tell the brain that a red apple vs yellow lemon was seen?) through 2 forms anatomical coding and temporal coding ANATOMICAL CODING www.notesolution.com The firing of a specific neuron tells the brain where the body is being touched By the means our brain represents the outer world Brain uses anatomical coding to locate which sense organ was activated. bc the brain has no direct info about physical energy. Example: you rub your eye, then you mechanically stimulate the light receptors that are in the eye area Definition: a means by which the nervous system represents information, different features are coded by the activity of different neurons TEMPORAL CODING The rate at which these neurons fire (whether fast or slow), tells us how intense the touch is The coding of info based on time Example: light touch= low firing rate of neurons === forceful touch= higher rate of neurons PSYCHOPHYSICS (physics of the mind) Is the study of the relation btw physical characteristics of stimuli and sensations they produce? To study perceptual phenomena, there are 2 methods 1. The principal of the Just-Noticeable Difference 2. Signal Detection Theory Ernst Weber- investigated the ability of humans to discriminate btw various stimuli measured it based on just noticeable difference Jnd= smallest difference btw 2 similar stimuli that can be distinguished or detected by a person, AKA difference threshold (example: to see whether ppl can tell the difference btw a 400 gram weight to 410 gram weight) - each dot marks another jnd. The amount of physical energy necessary to produce a jnd increases w magnitude of stimulus Weber Fractions: ratio btw jnd and magnitude of stimulus, reasonably constant over the middle range of most stimulus intensities Jnd is the difference btw the starting weight and the weight that ppl notice a difference. Example, starting weight is 100 and at 110 is when ppl start to notice the difference, TF the JND is 10. But instead of saying that the difference is 10, they use Webers fraction the ration of 10:100 where 10 is the difference, and 100 is the initial starting weight. Gustav Fechner used Webers Idea of jnd to measure ppls sensations (example: he kept turning the light intensity brighter and brighter to measure whether ppl can detect the difference and kept going until ppl couldnt stand the brightness anymore) Contribution to show how a logarithmic function could be derived from Webers principle S.S Stevens- modified the formulation and suggested a power function to describe the relation btw physical intensity and sensation b S= kI s= psychological magnitude of sensation i= intensity of physical stimulus k= mathematical constant that adjusts for the way physical intensity is measured SIGNAL DETECTION THEORY When calculating Reciever Operating Characteristic (ROC) curves, an experiment must be conducted first www.notesolution.com
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