Decisions In Signal Detection Theory
Brief description and instructions (DRAFT):
This applet illustrates how Signal Detection Theory explains the possible outcomes of a detection situation and how often an outcome will happen under different circumstances.
The main figure is very similar to the Signal Detection Theory applet. You can refer to that applet for instructions on how that part of this applet works.
There is one additional feature of this diagram, the criterion represented by the vertical yellow line. According to Signal Detection Theory, the observer sets the criterion at any desired point along the sensory strength dimension. The observer then uses the criterion as a cutoff. When the sensory strength is above the criterion, the observer will say that "yes" they detected the signal or stimulus. When the sensory strength is below the criterion, the observer will say that "no" they did not detect the signal.
The criterion then allows for the four possible outcomes. Hits happen when the signals is present (the signal+noise curve) and sensory signal strength is above the criterion. Misses happen when the signal is present, but the sensory strength is below the criterion. False alarms happen when no signal is present (the noise curve) but the sensory signal strength is above the criterion. Correct rejections happen when no signal is present and the sensory strength is below the criterion. Buttons on the left can be pressed to show which part of each curve is responsible for each decision.
At the bottom of the screens there are sliders that allow you to adjust the sensitivity and criterion to see how this affects the four outcomes. A table below the sliders show the predicted percentage of trials with signals that will be hits and misses and the percentage of trials without a signal that will yield false alarms and correct rejections. The colors of the percentages match the color of the same region when it is highlighted e.g, hits are in red and are highlighted in red.
Click here to open the applet. It will open a new window that will fill your screen.