Signal Detection Theory
Brief description and instructions (DRAFT):
This applet illustrates the basic features of Signal Detection Theory. When the applet first comes up, a graph is presented. The x-axis is a the sensory strength being experienced by the observer. The y-axis is the probability of a given sensory strength.
When the applet first comes up, only the noise curve is visible. This is the description of what is happening in the sensory system when no stimulus is present. There is still some activity in the sensory system, sometimes more, sometimes less. How likely a given level of sensory activity occurs is indicated by the height of the curve, the higher the more likely.
The buttons on the left side allow you to add and remove features of this graph. The Show Signal button will add the signal+noise curve. This represents what is happening in the sensory system when a stimulus, the signal, is presented. Clicking on the Remove Noise will show the situation when the stimulus is present. Notice that there is still noise in the sensory system. Having both the noise curve and the signal+noise curve present shows most clearly how the system changes when a stimulus is added. Pressing the Show Overlap button will create a shading that indicates how much the noise and the signal+noise curves overlap. In this region a given sensory strength could be caused by either noise or the stimulus. It is ambiguous. The strength of the stimulus can be controlled by the slider on the bottom labeled Sensitivity-d'. Moving the slider to the right increases the strength of the stimulus and decreases the overlap.
Click here to open the applet. It will open a new window that will fill your screen.