Polich 2016 updating p300
Since the initial discovery of this ERP component, research has shown that the P300 is not a unitary phenomenon.
Rather, we can distinguish between two subcomponents of the P300: the novelty P3, or P3a, and the classic P3, or P3b. Assuming that a cephalic reference is used (i.e., a reference electrode placed somewhere on the head, such as the tip of the nose or the chin), the P3b is a positive-going ERP whose latency at peak amplitude is usually about 300 ms to simple sensory stimuli.
The P3b can be observed in a variety of experimental contexts.
The most common paradigms will either present infrequent, task-relevant stimuli as a way to elicit a P3b, or they will employ two tasks at the same time to use P3b as a measure of cognitive workload.
This shows two important findings: first that this late positivity occurred when the uncertainty about the type of click was resolved, and second that even an absence of a stimulus, when it was relevant to the task, would elicit the late positive complex.
These early studies encouraged the use of ERP methods to study cognition and provided a foundation for the extensive work on the P3b in the decades that followed.
Generally speaking, improbable events will elicit a P3b, and the less probable the event, the larger the P3b.
However, in order to elicit a P3b, the improbable event must be related to the task at hand in some way (for example, the improbable event could be an infrequent target letter in a stream of letters, to which a subject might respond with a button press).
For example, subjects might see a string of letters presented one at a time.
They also found that the ERP responses to the numbers, but not to the light flashes, contained a large positivity that peaked around 300 ms after the stimulus appeared.
They also noted that the amplitude of this positivity was not affected by the intensity of the stimulus.
The P3b is typically observed around 300 ms after each presentation of the target (oddball) stimulus.
A three-stimulus oddball task is exactly like the two-stimulus oddball task, except that in addition to the targets and standards, an infrequent, deviant stimulus such as the letter "D" will appear.
The P3b has been a prominent tool used to study cognitive processes for several decades.