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Chapter 4


11 Pages

Course Code
PSYC 1010
Rebecca Jubis

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Psychology 1010Chapter 4 SensationPerceptionPsychophysics Basic Concepts and Issuesy Psychophysics is the study of how physical stimuli are translated into psychological experienceThresholds looking for Limitsy A threshold is a dividing point between energy levels that do and do not have a detectable effect o Hardware stores sell a gadget with a photocell that automatically turns a lamp on when a room gets dark The level of light intensity at which the gadget clicks on is its threshold y An Absolute Threshold for a specific type of sensory input is the minimum amount of stimulation that an organism can detect o Defines the boundaries of an organisms sensory capabilities o When lights of varying intensity are flashed at a subject there is no single stimulus intensity at which the subject jumps from no detection to completely accurate detection Instead stimulus intensity increases subjects probability of responding to stimuli gradually increaseso Absolute threshold is arbitrary defined as the stimulus intensity detected 50 of the timeWeighing the Differences The JNDy JNDA just noticeable difference is the smallest difference in the amount of stimulation that a specific sense can detect JNDs are close cousins of absolute thresholds y Webers Lawstates that the size of a just noticeable difference is a constant proportion of the size of the initial stimuluso This constant proportion is called the weber function o Webers law applies not only to weight perception but to all of the senses o However different fractions apply to different types of sensory inputThe weber fraction for lifting weights is approximately 130 that means that you should be just able to detect the difference between a 300gram weight and a 310gram weightPsychophysical Scalingy Fechners Law states that the magnitude of a sensory experience is proportional to the number of JNDs that the stimulus causing the experience is above the absolute threshold o Constant increments in stimulus intensity produce smaller and smaller increases in the perceived magnitude of sensationo Three equal increases in stimulus intensity the amount of light produce progressively smaller differences in the magnitude of sensation perceived brightnessSignalDetection Theory y Proposes that the 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 y Subliminal perceptionthe registration of sensory input without conscious awareness o Subliminal means below thresholdSensory Adaptation y Is a gradual decline in sensitivity due to prolonged stimulation o When you put your clothes on in the morning you feel them initially but the sensation quickly fades o Sensory adaptation is an automatic builtin process that keeps people tuned in to the changes rather than he constant in their sensory inputo Allows people to ignore the obvious and focus on changes in their environment that may signal threats to safetySummary y Psychophysicists use a variety of methods to relate sensory inputs to subjective perceptions They have found that absolute thresholds are not really absolute y Webers law states that the size of a just noticeable diff is a constant proportion of the size of the initial stimulusy Fechners law asserts that larger and larger increases in stimulus intensity are required to produce just noticeable differences in the magnitude of sensationy According to signaldetection theory the detection of sensory inputs is influenced by noise in the system and by decisionmaking strategies y Signal detection theory replaces Fechners sharp threshold with the concept of detectability and emphasizes that factors beside stimulus intensity influence detectability
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