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Chapter 4

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University of Toronto Mississauga
Dax Urbszat

Psychology Chapter 4 Notes Sensation and Perception Astronauts in space experience a reduction in their handeye coordinationIan Howard psychologist researching the role of visual cues in spatial orientationAstronauts loose sense of what it up and down because there is no gravity in space this can lead to disorientation difficulty in task performance and motion sicknessPeople rely on three types of cues to determine which way is up visual gravitybody directionSensation is the stimulation of sense organs o Involves the absorption of energy such as light or sound waves by sensory organs like the ears and eyesPerception is the selection organization and interpretation of sensory input o Involves organizing and translating sensory input into something meaningful such as a face Psychophysics the study of how physical stimuli are translated into psychological experienceSensation begins with a stimulus any detectable input from the environment o However detectable depends on who or what is doing the detecting a human cant smell a weak odour but a dog can o Thus Gustav Fechner what is the weakest detectable stimulus o Threshold is a dividing point between energy levels that do and do not have a detectable effectthe point at which a stimulus is of sufficient intensity to begin to produce an effect o Absolute Threshold for a specific type of sensory input is the minimum amount of stimulation that an organism can detectthe smallest detectable level of a stimulus For example in an experiment on sound detention researchers may present a sound with varying levels of volume The smallest level that a participant is able to hear is the absolute thresholdThere is no single stimulus intensity where at which a subject goes from no detection to complete detection As the stimulus increases the subjects ability to detect it gradually increasesWHEN THE STIMULUS IS DETECTED 50 OF THE TIME Weighing the Differences JNDA just noticeable difference JND is the smallest difference in the amount of stimulation that a specific sense can detect o Discovered by Ernst Weber o Webers Law states that the size of a JND is a constant proportion of the size of the initial stimulus The constant proportion is called the Weber Fraction o For example the weber fraction for lifting weight is 130 that means you should just be able to detect the difference between a 300g and 310g weightTo calculate this you take 300g and find what 130 of 300 is13030010g so a 10 g increases900g weight o 13090030g so a 30g increaseas a stimulus increases in magnitude the JND becomes largerFechners Law related JND to scaling of sensory experience o States that the magnitude of a sensory experience is proportional to the number of JNDs that the stimulus causing experience is above the absolute threshold Constant increases in stimulus intensity produce smaller and smaller increases in perceived magnitudePerceptions cant be measured on absolute scales everything is relativeSignalDetection Theory 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 intensity When observing something to find a certain object four things can happen hits detecting the object when it is present missesnot detecting the object false alarms detecting the object when it is not there and correct rejectionDetectability is measured in terms of probability and depends on decision making processes as well as sensory processesSubliminal Perception the registration of sensory input without conscious awareness o Used in marketing to elicit favourable reactionsFor example a study done by Stroebe and Claus one group of subjects was shown pictures with the word LIPTON ICE hidden in the background of the pictures the other group wasnt The group shown the word drank Lipton Iced Tea more than the group not shown the word Subliminal stimulation generally produces weak affectsSensory Adaption is a gradual decline of in sensitivity due to prolonged stimulationo For example you smell the garbage in you kitchen if you do not remove it and stay in the kitchen for a while the stench will go away The smell is still the same but you sensitivity to the smell has decreased Sensory adaption is an automatic builtin process that keeps people tuned in to the changes by ignoring the obvious and focusing on the changes in the environment that may signal threat to safety
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