Source: Laboratories of Jonas T. Kaplan and Sarah I. Gimbel—University of Southern California

Given the overwhelming amount of information captured by the sensory organs, it is crucial that the brain is able to prioritize the processing of certain stimuli, to spend less effort on what might not be currently important and to attend to what is. One heuristic the brain uses is to ignore stimuli that are frequent or constant in favor of stimuli that are unexpected or unique. Therefore, rare events tend to be more salient and capture our attention. Furthermore, stimuli that are relevant to our current behavioral goals are prioritized over those that are irrelevant.

The neurophysiological correlates of attention have been experimentally examined through the use of the oddball paradigm. Originally introduced in 1975, the oddball task presents the participant with a sequence of repetitive audio or visual stimuli, infrequently interrupted by an unexpected stimulus.¹ This interruption by a target stimulus has been shown to elicit specific electrical events that are recordable at the scalp known as event-related potentials (ERPs). An ERP is the measured brain response resulting from a specific sensory, cognitive, or motor event. ERPs are measured using electroencephalography (EEG), a noninvasive means of evaluating brain function in patients with disease and normally functioning individuals. A specific ERP component found across the parietal region of the scalp, known as the P300, is enhanced in response to oddball events. The P300 is a positive-going deflection in the EEG signal that occurs about between 250 and 500 ms after stimulus onset. In general, early potentials reflect sensory-motor processing while later potentials like the P300 reflect cognitive processing.

In this video, we show how to administer the oddball task using EEG. The video will cover the setup and administration of EEG, and analysis of ERPs related to both control and target stimuli in the oddball task. In this task, participants are set up with the EEG electrodes, then brain activity is recorded while they view control stimuli, interspersed with target stimuli. The procedure is similar to that of Habibi et al.² Each time a target stimulus is presented, the participant presses a button. When the ERPs are averaged across the control and target stimuli, the neural correlates of each event can be compared in a selected time window.

1. Participant recruitment

1. Recruit 20 participants for the experiment.
2. Make sure that the participants have been fully informed of the research procedures and have signed all the appropriate consent forms.

2. Data collection

1. EEG preparation (Note: These steps are for use with the Neuroscan 4.3 system with Synamps 2 amplifier and a 64-channel quick cap.)
   1. Participants in an EEG study should not have any hair products (e.g., gel, mouse

During the oddball task where participants were instructed to respond with a button press each time they saw a green circle, there was an increased parietal P300 compared to when the participant viewed the control red circle. This trace peaked approximately 350 ms following the onset of the stimulus, whereas there was no P300 peak for the control trace (Figure 3).

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The ERP approach, due its very high temporal resolution, allows discrimination between the electrical events that correspond to extremely fast psychological processes. The oddball task demonstrates this power, in revealing an electrical signature from the parietal lobe that discriminates between two similar stimuli less than half a second after their presentation. The task provides a window into the brain's process for identifying features in the environment that have current biological importance.³