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Chapter 4

Chapter 4

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Dan Dolderman

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Chapter 4 Sensation and PerceptionPsychophysics Basic Concepts and Issues Thresholds Looking for Limits Thresholddividing point between energy levels that do and do not have a detectable effect Absolute thresholdminimum amount of stimulation that an organism can detectnot absolute as stimulus intensity increases subjects probability of responding to stimuli increases Weighing the Differences The Just Noticeable Difference JNDJNDsmallest difference in the amount of stimulation that a specific sense can detectWebers lawthe size of a JND is a constant proportion of the size of the initial stimulusPsychophysical ScalingFechners lawthe magnitude of a sensory experience is proportional to the number of JNDs that the stimulus causing the experience is above absolute threshold SignalDetection TheorySignaldetection theorythe detection of stimuli involves decision processes as well as sensory processes which are both influenced by a variety of factors besides stimulus intensityPerception without Awareness Subliminal perceptionthe registration of sensory input without conscious awarenessPeople are defenceless against appeals operating below their threshold of awarenessSensory Adaptation Sensory adaptationa gradual decline in sensitivity to prolonged stimulationReview of Key PointsPsychophysicists have found that absolute thresholds are not really absoluteWebers law states that the size of a just noticeable difference is a constant proportion of the size of the initial stimulus Fechners law asserts that larger and larger increases in stimulus intensity are required to produce just noticeable differences in the magnitude of sensation According to signaldetection theory the detection of sensory inputs is influenced by noise in the system and decisionmaking strategies It replaces Fechners threshold with the concept of detectability and emphasizes that factors besides stimulus intensity influence detectability In recent years a host of researchers using very different conceptual approaches have demonstrated that perception can occur without awareness However research indicates that the effects of subliminal perception are relatively weak and of little or no practical concernProlonged stimulationsensory adaptation involves reduction in sensitivity to constant stim
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