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Chapter 4

Chapter 4- Sensation and Perception.docx

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University of Toronto St. George
Maja Djikic

Chapter 4 Sensation and PerceptionIan HowardInvolved in space researchPioneer in sensationperception researchOrdinarily people rely on 3 types of cues to determine which way is upVisual gravity and body directionPeople differ in terms of how they perceive 3D imagesSensationthe stimulation of sense organsinvolves the absorption of energy such as light or sound waves by sensory organs such as the ears and eyesPerceptionthe selection organization and interpretation of sensory inputinvolves organizing and translating sensory input into something meaningful such as your best friends face or otherenvironmental stimuliPsychophysicsthe study of how physical stimuli are translated into psychological experienceGustav Fechner important contributor to thisThresholdSensation begins with a stimulus any detectable input from the environmentFechner wanted to know for any given sense what is the weakest detectable stimulusThreshold a dividing point between energy levels that do and do not have a detectable effectAbsolute Threshold for a specific type of sensory input is the minimum amount of stimulation that an organism can detect stimulus intensity detected 50 of the timeWhen lights of varying intensities are flashed at a subject there is no single stimulus intensity at which the subject jumps from no detection to complete accurate detection As stimulus intensity increases subjects probability of responding to stimuli gradually increasesAbsolute Threshold for Senses Vision candle flame seen at 50km on a dark clear night Hearing tick of a watch under quiet conditions at 6m Taste 5mL of sugar in 75 L of water Smell One drop of perfume diffused into the entire volume of a sixroom apartment Touch The wing of a fly falling on your cheek from a distance of 1cmJust Noticeable DifferenceFechner was interested in peoples sensitivity to differences in stimuliJust Noticeable Difference smallest difference in the amount of stimulation that a specific sense can detectAbsolute threshold is the JND from nothing no stimulusFirst Principle Ernst Weber Webers Law the size of a jnd is a constant proportion of the size of the initial stimulusConstant proportion known as Webers fraction130 of any weight Ex 130 of 30010 130 of 900 30 therefore cannot detect difference between 900 and 910 but can detect difference between 300 and 310Psychophysical ScalingIf one light has twice the energy of another does that mean it is twice as brightScale the magnitude of sensory experiencesFechners Law the magnitude of a sensory experience is proportional to the number of JNDs that the stimulus causing the experience is above the absolute thresholdComplication of Fechners Law constant increments in stimulus intensity produce smaller and smaller increases in the perceived magnitude of sensationSignalDetection TheoryPerceptions cant be measured on absolute scalesSignaldetection theory the detection of stimuli involves decision processes as well as sensory processes which are both influenced by a variety of factors besides stimulus intensityIn situations there are 4 possible outcomes for detecting signals 1 Hit detecting a signal when it is present 2 Miss failing to detect a signal when it is present 3 False Alarm
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