You are downstairs watching a movie. The volume is up on your surround sound system and you don’t have a phone in the room. At a moment of great tension and excitement, and perhaps volume, you think you hear the phone. You are not sure. What are you to do?
Most of the time, we are aware of our surroundings. You can easily identify the door in the room you are in. It is obvious, but there are times when something happens, like the phone ringing, and you have to decide if something has actually happened. Signal detection theory was developed to explain these ambiguous situations.
This activity will use a simulated experiment to guide you through the elements of signal detection theory and how it describes how you determine if you think the phone actually rang.
References:
Green, D. M., & Swets, J. A. (1966). Signal detection theory and psychophysics. Oxford England: John Wiley.
Experiment Setup
Figure 1.1
Instructions
Instructions
In this experiment, you have to determine if something has changed on the screen. The situation is very simple. Dots will flash on the screen in front of you; sometimes there will be more dots than others. It is all random. Your job is to determine if the experimenter has added any dots to the screen.
Please follow the instructions on the experiment tab as you go through the activity to illustrate the elements of signal detection theory.
Experiment
Begin Experiment
Start Experiment
Figure 1.2
Results
Results
Figure 1.3
Quiz
Quiz
Question
1.1
The measure of how sensitive you are to a stimulus in signal detection theory is called:
A.
B.
C.
D.
1
Correct.
Incorrect.
In signal detection theory, the way we measure our ability to detect a stimulus, or our sensitivity, is called d’.
Question
1.2
If a stimulus is not present but you say it is, this is called a:
A.
B.
C.
D.
1
Correct.
Incorrect.
There is no stimulus to report but you say there is. This is a classic description of the boy who cried wolf or false alarm.
Question
1.3
What happens to the noise in our system when a simulus or signal is presented?
A.
B.
C.
D.
1
Correct.
Incorrect.
The presence of noise in our systems is completely unaffected by the stimulus according to signal detection theory so nothing happens to the noise when a stimulus is presented.
Question
1.4
If I adjust my criterion so that I make fewer false alarms, what happens to my ability to have hits?
A.
B.
C.
D.
Correct.
Incorrect.
Generally, if I adjust my criterion so that false alarms go down, I also make fewer hits.
Question
1.5
As sensitivity increases, how does the ROC curve change?
A.
B.
C.
D.
Correct.
Incorrect.
As sensitivity increases, the ROC curve bows out from the positive diagonal which is the line that represents no sensitivity to the stimulus.
