Soq€ o Group II Three subjects participated in a study in which they judged whet
ID: 3349961 • Letter: S
Question
Soq€ o Group II Three subjects participated in a study in which they judged whether or not the letter M was presented in a background of visual noise. A total of 200 trials were run with the letter presented on half of the trials (100). Results for each of the three participants are shown below: 75|| 00 0.75 Subject A Trial Type Response NOISE-ONLY NOISE+M "NOISE ONLY" 60 75 40 "NOISE+M" 25 Subject B Response "NOISE ONLY" "NOISE+M" Trial Type NOISE-ONLY NOISE+M 20 80 80 20 Subject C Response "NOISE ONLY" “NOISE+M" Trial Type NOISE-ONLY NOISE+M 40 20 80 60 Remember that Hit Rate is computed as the number of Hits divided by the total number of Signal + Noise trials (NOISE + M trials, in the current context) and False Alarm Rate is computed as the number of False Alarms divided by the total number of Noise-Only trials. Compare these three participants in terms of their ability to discriminate the Noise- only from the Noise+M states of world as measured by d’. Also compare them in terms of criterion, the tendency to respond “Signal+Noise" vs. "Noise-alone," as assessed by B.Explanation / Answer
Comparison in terms of d' :
From the basics of signal detection theory, higher the value of d', better is the ability of the participant to discriminate Noise Only from the Noise+M states of world. From the given data, for subject A, value of d' is 0.70630256, which is lesser than the value of d' 1.41260513 for subjects B and C. Therefore, discrimination ability of subject A is inferior to both subjects B and C. However, since, subject B and C, both have same value of d', both of them have equal ability for dicrimination.
Comparison in terms of Beta :
Beta the measure of the threshold that the participant uses in order to determine whether the signal is present or not. For eg. , the Beta value of 1.75 always means that there is a 4% chance of responding "signal" , when it is not present because 1.75 is 96th percentile in the standard normal distribution. Therefore, lesser the value of Beta, more is the tendency to respond "Signal+Noise" than "Noise-alone".
As per the given data, the Beta values for subjects A, B and C are 0.77924354, 1 and 1 respectively. And hence, subject A has more tendency to respond "Signal+noise" than "Noise-alone" compared to subjects B and C. However, since B and C both have same value of Beta , they have same tendency to respond "Signal+noise" than "Noise-alone".
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