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Lecture 2 - 05.01.11

Lecture 2 - 05.01.11 - 5th January 2011 Psych 120B Lecture...

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5 th January 2011 Psych 120B – Lecture 2 Psychopsychics and Psychophysical Methods Measurement in Sensation and Perception Basic psychophysics o Fechner o Threshold concepts o Classical psychophysical methods Psychophysical scaling o Weber’s law o Scales of magnitude o Steven’s law Response problems Psychophysics Study of sensations evoked by physical stimuli o E.g., light intensity, mechanical pressure Accuracy and reaction time are usually the dependent variables. These are what are usually measured in experiments: how well they do it and how fast they do it. Measurement Sensation: sensory limits o What is the dimmest light you can detect? o What is the smallest difference in pitch you can distinguish? Perception: what is out in the world? o Which object is farther away? o Is one object bigger than another? We measure these with PSYCHOPHYSICS and SIGNAL DETECTION THEORY Original Emphasis: Sensory Limits E.g., smallest detectable amount of light energy Methods were developed in this connection: to measure sensation (dim light, pitch differences, etc.) These were very useful and then applied to measure other things like the limits of perception. Basic Psychophysics – Gustav Fechner (1801-1887) “Exact quantitative relation between matter and mind” - psychophysics Invented many of the basic concepts we use today because they are still very accurate and useful. Threshold Concepts Absolute threshold – basically what we think about when we think about threshold. How bright does a light have to be for us to see it and how loud does a sound have to be for us to hear it? Difference threshold – how sensitive we are and at what point are we able to notice a difference in a stimulus. How much does a stimulus have to increase/decrease before you notice the difference? How would YOU measure threshold for, say, detecting a light spot?
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Psychophysical Methods Constant stimuli Limits Adjustment Methods of Limits E.g., detecting a light spot In each trial, present a light spot, ask for response and then incrementally o Increase intensity until just visible o Decrease intensity until just invisible o Back and forth o Take the average, this is the 50% threshold – the crossover, which is where the subject’s answer changes from yes to no or vice versa. Method of Adjustment
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Lecture 2 - 05.01.11 - 5th January 2011 Psych 120B Lecture...

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