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CHAPTER 1 Basic Concepts in PerceptionNave Realism sensation is simple and directI see it because it is thereIllusions prove that this is incorrectMethods in Perception1Qualitative ObservationGetting the big pictureNonsystematic observation of a given perceptual phenomenon ex illusionThreshold seeking methods2Qualitative MethodsUnderstanding the detailsFlowers look different at night than during the day exampleoTwo visual systems existThresholdSeeking Methods measure a physical quantity representing a limit of perceptual abilityAbsolute threshold smallest detectable physical quantitySubthreshold below absolute thresholdSuprathreshold above absolute thresholdDifference threshold smallest detectable difference between two physical quantitiesoAKA Just Noticeable Difference JNDoNot a constant value it is a constant proportion50 threshold the physical quantity detectable 50 of the timeClassic Methods Fechner 1850s1Method of Adjustments Quick and dirtyStimulus intensity is adjusted continuously until participant says he can just detect itRepeat trials averaged for thresholdGives a rough estimate2Method of LimitsEasy on observer fairly fast and accurateStimuli of different intensities presented in ascending and descending orderObserver responds to whether she perceives the stimulusyes noAverage of crossover points from several sequences is taken to obtain final thresholdCalculated by taking thebetween the last visible stimuli and the first unrecognizable stimuli ex 99989853Method of Constant StimuliVery slow but very accurate5 to 9 stimuli of different intensities are presented many times each in random orderMultiple trials often 100s of each intensity are presentedParticipant does not control intensitiesGives very specific resultsResponse BiasLax criterion tend to say yes I see it a lotStrict criterion tend to say no I dont see it a lot1Forced Choice VariationsParticipant is given several options to choose fromEven if you cannot see anything you have to say somethingWebers Law describes the relationship between stimulus intensity and difference threshold as Fechners Law subjective perception is related to stimulus intensity according to Sk x In IIo Kempirically determined free parameterIstimulus intensityIostimulus intensity at absolute thresholdInLog to base eWorks well for many sensations loudness pressure weight but not for others electric shock that show response expansionModels the response of individual neurons rather than peopleMagnitude EstimationResponse Compression as intensity increases the perceived magnitude increases more slowly then the intensityResponse Expansion as intensity increases the perceived magnitude increases more quickly than the intensitySUMMARYThe 3 Laws of Psychophysics1Webers Law relates two physical units standard stimulus intensity and difference threshold2Fechners Law relates a physical unit stimulus intensity with subjective intensity3Stevens Power Law covers stimulus that show response expansion as well as more closely modeling human responsesSensitivity measure of ones ability to detect a given signal usually at low intensitySymbolized by d deeprimeMeasuring SensitivityTest Trials present stimulus signal on only half of the trialsCatch Trials present no stimulus noise on other half of trialsoFor each trial the participant must say yes or no regarding if the stimulus is thereFour Possible Results on Each TrialThe stimulus is reallyPRESENTABSENTYES I SEE ITHitFalse alarmNO I DONTMissCorrect RejectionThe results of this experiment yield Proportion of hits PhitstrialsProportion of false alarms Pfalsealarmstrials2
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