Updating p300 an integrative theory of p3a and p3b
However, using a 15-electrode setup with a linked-earlobe reference and an oddball task (described below), researchers have also found that the positivity increased moving from frontal to parietal sites, and that females have a greater increase than males.
Thus, the exact distribution may be dependent upon the task, as well as the gender and age of the subjects.
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.
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.
For every two numbers, the subjects were required to make simple decisions, such as telling which of the two numbers was numerically smaller or larger, which came first or second in the sequence, or whether they were equal.
The P3b is a positive-going amplitude (usually relative to a reference behind the ear or the average of two such references) peaking at around 300 ms, though the peak will vary in latency (delay between stimulus and response) from 250–500 ms or later depending upon the task.
Amplitude has been defined as the difference between the mean pre-stimulus baseline voltage and the voltage of the largest (in this case, positive-going) peak of the ERP waveform in a specific time window.), but varies systematically as a function of a number of important factors (see Functional significance: Factors that influence amplitude).
Latency has been defined as the time from the onset of the stimulus (or whatever the desired point of measurement might be) to the point of maximum amplitude.
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.
Search for updating p300 an integrative theory of p3a and p3b:
Chapman and Bragdon speculated that this differential response to the numbers, which came to be known as the P300 response, resulted from the fact that the numbers were meaningful to the participants, based on the task that they were asked to perform.