Another important finding from these studies is that this late positive complex was observed for both the clicks and flashes, indicating that the physical type of the stimulus (auditory or visual) did not matter.
Subjects viewed these stimuli one at a time in a sequence.
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 presence, magnitude, topography and timing of this signal are often used as metrics of cognitive function in decision making processes.
While the neural substrates of this ERP component still remain hazy, the reproducibility and ubiquity of this signal makes it a common choice for psychological tests in both the clinic and laboratory.
has a positive-going amplitude that displays maximum amplitude over frontal/central electrode sites and has a peak latency in the range of 250-280 ms.
The P3a has been associated with brain activity related to the engagement of attention (especially the orienting, involuntary shifts to changes in the environment), and the processing of novelty.
P300 latency and amplitude trajectories across the lifespan as obtained from the cross-sectional dataset.
Dots represent scores from individual participants. From From P300 Development across the Lifespan: A Systematic Review and Meta-Analysis.
The second cue type had probabilities that were the reverse of the first.
They found that the amplitude of the positive complex was larger in response to the less probable stimuli, or the one that only had a 1 in 3 chance of appearing.
This shows two important findings: first, that this late positivity occurred when uncertainty about the type of click was resolved, and second, that even an absence of a stimulus would elicit the late positive complex, if said stimulus was relevant to the task.