Final answer:
A true positive in signal detection theory is when a stimulus that is present is correctly detected, such as correctly identifying an airplane on radar or a pregnancy with a lateral-flow test.
Step-by-step explanation:
In signal detection theory, the outcome of correctly detecting a stimulus that is present is known as a true positive. In other words, when a signal or stimulus exists and the observer detects it, this is a true positive result. This concept is fundamental in various applications such as medical tests, where a true positive would indicate that a condition being tested for, such as pregnancy in a lateral-flow pregnancy test, is indeed present if the test line appears. Conversely, if there is no test line, as with the example of the pregnancy test without a blue band on the test line, it is not a true positive and likely indicates a negative test for pregnancy. Signal detection theory also has implications in settings like air traffic control, where accurate detection of planes on a radar amidst numerous signals is critical.