Signal Detection Theory




SDT Outcomes


Is there a Threshold?




Note: The interactive figures in this tutorial require Sun's Java 2 not Microsoft's.  JavaScript routines will determine if you have the proper version of Java and if not ask if you want to download it from Sun Microsystems.  It is a safe download. 


The theory of signal detection theory evolved from the development of communications and radar equipment the first half of this century.  It migrated to psychology, initially as part of sensation and perception, in the 50's and 60's as an attempt to understand some of the features of human behavior when detecting very faint stimuli that were not being explained by traditional theories of thresholds.

The situation of interest is this:

A person is faced with a stimulus that is very faint or confusing.  For simplicity's sake lets us call this stimulus a signal.  The person must make a decision, is the signal there or not.  What makes this situation confusing and difficult is the presences of other mess that is similar to the signal.  Let us call this mess noise.  

What makes this different from traditional threshold theories is that the subject makes a decision, a cognitive act, as to whether the signal is present or not.  This basic sensory act of determining if a stimulus occurred now is understood to have a cognitive component.

If you want a concrete example, click here.

Now what can happen in this situation.  If the signal is present the person can decide that it is present or absent.  These outcomes are called hits and misses.  If the signal is absent the person can still decide that the signal is either present or absent.  These are called false alarms or correct rejections (CR) respectively.  

A common way to display these outcomes is below in Table 1.

Present Absent
Decision: Present Hit False Alarm
Absent Miss Correct Rejection

Where to from here:

Background Basics of Theory Concrete Example