PSY Ch. 3 Sensation and Perception

PSY Ch. 3 Sensation and Perception - I. Psychology Ch. 3...

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Psychology Ch. 3 Sensory I. Psychophysical Research a. The Detection Question: What’s the dimmest light we can see or softest sound we can hear, e.g. i. Absolute threshold : psychologists hypothesized that there was an absolute threshold – if a stimulus was over the threshold, people could detect it 100% of the time, if it was below 0% of the time. In reality the percentage of “yeses” increased as the amount of energy in the stimulus increased, leading the scientists to devise a statistical absolute threshold the minimum amount of energy in a sensory stimulus detected 50% of the time (has an equal probability of being detected or not detected). ii. Humans are good detectors of weak stimuli iii. Subliminal stimuli are stimuli detected less than50% of the time iv. There is no evidence to support subliminal persuasion theories v. Signal Detection Theory – our ability to detect a faint sensory signal is a decision-making process that depends upon a person’s physiological sensitivity to the signal AND upon the person’s decision-making criterion which is based on nonsensory factors such as personality 1. the advantage here is that it provides two quantitative measures, one for physiological sensitivity and one for his decision criterion 2. a person with very lax decision criterion will say yes (false alarms) more often than someone with strict criterion, who will have misses 3. the bottom line is that our perception of even a faint signal is a subjective process impacted by nonsensory factors b. The Difference Question i. What’s the smallest difference in brightness between two lights tat we can detect? ii. Different threshold the minimum difference between two stimuli detected 50 % of the time iii. Weber’s Law 1. when measuring a person’s difference threshold, psychophysicists presented two stimuli on each trial and varied the amount of difference between them across trials by keeping the intensity of one the same on every trial and changing the intensity of the other one across trials (the standard and comparison stimulus, resp) 2. weber’s law – for each type of sensory judgment that we can make the measured difference threshold is a constant fraction of the standard stimulus value used to measure it; a smaller constant means that smaller differences can be detected a. brightness = .08 b. loudness of tones = .05 c. lifted weights - .02 d. WEBER’S HOLDS FOR MOST TYPES OF SENSORY JUDGMENTS BUT NOT FOR VERY LOW- OR HIGH- INTENSITY STIMULI c. The Scaling Question How to perceptual scales of measurement relate to physical scales of measurement?
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i. Stevens’s Power Law : the perceived magnitude of a stimulus if equal
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PSY Ch. 3 Sensation and Perception - I. Psychology Ch. 3...

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