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Psychology 2115A/B
Stephen Lupker

Lecture: 4 September-19-11 2:29 PM Signal Detection Theory  A way of filtering out bias  We have a basic background noise, it is a random noise that our auditory system displays  It boosts it out in a constant sound  It adds an amount of noise to your system, and then added to our stimulus noise  This is the situation we have here  The experimenter now has to decide if there was an actual noise or not, this is now making it very unclear for them  They then have to tell the observer if they think they heard something or not  Then Beta comes in, in which if the person gets anything below the Beta then they will say no and if it higher than the person will say yes  "d" prime is supposed to stay the same, what is changing is Beta,  Beta reflects Biases  If a person says no or yes a lot of the time  You need to calculate the Probability of your impression given your stimulus and the probability of your impression given no stimulus or noise  Then you need to make a ratio by putting one over the other and seeing if it is smaller or bigger then one e.g. P(i/s)/ P )i/N)  This is called a likelihood ratio  When an observer tells you that their is 80 of the trials have a stimulus and only 20% of the time there isn't  It will make the experimenter lean and change their Beta  So now when things are presented 80% of the time you get P(i)/s) p(s) all over p(i/N) p(n)  The second way of doing this is by differential payoffs  See chart Scaling  Question: what is the relationship between the stimulus intensity and our subconscious intensity  F(S)=R (formulate a stimulus must produce a response)  What describes the relationship  The problem is that when you are trying to do this, is what is the psychophysical function?  When I get you an experiment, until you actually do something, the observer cannot figure out what is going on in you head, you must give a response  This is not simple it is full of biases  What process did you go through to take your function and come up with an eternal response  Fechner thought you couldn't do this since there was so much bias  Asked to pick a number between 1 to ten  Most people tend to pick seven or three  When we produce a number we
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