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Chapter 4

Psychology Chapter 4.docx

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Ryerson University
PSY 217
Jalene Ray

Psychology Chapter 4: Sensation and Perception - Sensation is the stimulation of sense organs - Perception is the selection, organization, and interpretation of sensory input Psychophysics: Basic Concepts and Issues - Psychophysics – the study of how physical stimuli are translated into psychological experience Thresholds: Looking for Limits - A threshold is a dividing point between energy levels that do and do not have a detectable effect - An absolute threshold for a specific type of sensory input is the minimum amount of stimulation that an organism can detect  Define the boundaries of an organism’s sensory capabilities Weighing the Differences: The JND - A just noticeable different (JND) is the smallest difference in the amount of stimulation that a specific sense can detect - JNDS are close cousins of absolute thresholds - JNDs vary by sense, and the smallest detectable difference is a fairly stable proportion of the size of the original stimulus - Weber’s Law: states that the size of a JND is a constant proportion of the size of the initial stimulus  Therefore, as stimuli increase in magnitude, the JND becomes larger Psychophysical Scaling - Fechner’s Law: states that the magnitude of a sensory experience is proportional to the number of JNDs is that the stimulus causing the experience is above the absolute threshold Ex: you are in a dark room with a single lamp that has three bulbs of the same wattage. You turn a switch and one bulb lights. After a dark room, the difference is striking. Turn again, and a second bulb comes on. The amount of light is doubled, but the room does not seem twice as bright. When you turn the third bulb on, it adds just as much light as the first or second, but you barely notice the difference - What this means is that perception cannot be measured in scales  in the domain of sensory experience, everything is RELATIVE! Signal-Detection Theory - Signal-detection 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 - Responses depend in part on the criterion you set for how sure you must feel before you react - Setting this criterion involves higher mental processes rather than raw sensation and depends on your expectations and on the consequences of missing a signal or of reporting a false alarm Perception without Awareness Can sensory stimuli that fall beneath the threshold of awareness still influence behaviour? - Subliminal (subliminal means below threshold) perception – the registration of sensory input without conscious awareness - there is evidence that perception without awareness can take place Sensory Adaptation - Sensory adaptation is a gradual decline in sensitivity due to prolonged stimulation Ex: if you jump reluctantly into a pool of cold water, you’ll find that the water temperature feels fine a few minutes later after you adapt to it Review of Key Points  Psychophysicists use a variety of methods to relate sensory inputs to subjective perception. They have found that absolute thresholds are not really absolute.  Weber’s law states that the size of a JND is a constant proportion of the size of the initial stimulus. Fechner’s law asserts that larger and larger increases in stimulus intensity are required to produce just noticeable differences in the magnitude of sensation.  According to signal-detection theory, the detection of sensory inputs is influenced by noise in the system and by decision-making strategies.  Signal-detection theory replaces Fechner’s sharp threshold with the concept of detectability and emphasizes that factors beside stimulus intensity influence detectability  Perception can occur without awareness, however, research indicates that the effects of subliminal perception are relatively weak and of little or no practical concern  Prolonged stimulation may lead to sensory adaptation, which involves a reduction in sensitivity to stimulation The Visual System: SIGHT Stimulus - Light is electromagnetic radiation that travels in waves - Humans can register only a slim portion of the total range of wavelengths from 400 to
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