Effects of complexity of visual distracters on attention and information processing speed reflected in auditory p300

The primary aim of this study was to assess the effects of continuous, visual distracters that change systematically in complexity on P300 responses generated by an auditory oddball paradigm. In addition, the type of attention given to the visual distracter was explored. It was hypothesized that P300 amplitudes would be smallest, latencies longest, and changes in scalp distribution greatest when the most complex visual distracter requiring active attention was used versus the simple visual distracter requiring passive attention.

Auditory-evoked P300s were collected in a sample of 10 healthy adults (mean age = 19.90 years) using a two-toned oddball paradigm (1500 Hz "frequent" tone, probability of occurrence: 0.88, and 2000 Hz "rare" target tone, probability of occurrence: 0.12). The oddball paradigm was paired with three different visual distracters, increasing in complexity. The simplest was a black fixation cross on a white background that participants were asked to view passively as they performed the auditory task of counting the target stimulus. The second visual distracter increased in complexity by introducing color and motion, as tan and medium pink squares were alternated on the screen. Participants had to actively attend to the alternating squares by looking for a hidden text message while simultaneously counting the target auditory stimulus. The third visual distracter condition increased complexity again by introducing not only color and motion, but also biological relevance as participants viewed a mouth producing nonsense syllables. Participants had to actively attend to the moving mouth to determine what it was producing while simultaneously counting the rare auditory stimulus.

The two more complex visual distracters that required active attention caused reductions in auditory-evoked P300 amplitudes relative to those recorded while the participants passively viewed a fixation cross. P300 amplitudes were similar whether the two more complex visual distracters (squares versus mouth) were used. P300 latencies and scalp distribution were not influenced by complexity of, or type of attention to, the visual distracter. Regardless of distracter condition, P300 amplitude was significantly smaller and P300 latency was significantly shorter at frontal sites when compared with central and parietal sites.

Findings indicate that endogenous attentional resource allocation abilities can be effectively monitored through the addition of a complex, visually distracting task to a "classic" auditory P300 paradigm. Biological relevance of the distracting task does not seem to have an effect on the event-related potentials measured in this study, suggesting other aspects, such as whether or not a stimulus contains color or motion, may determine the efficiency of the distracter. Last, by increasing the complexity of, and amount of attention to, a visual distracter while evoking P300s using auditory stimuli, the cognitive load for the normal, healthy listener seems to be increased and the response amplitude subsequently reduced. Evoking P300s under similar conditions from disordered populations with subtle cognitive deficits (e.g., mild traumatic brain injury) may allow for increased diagnostic specificity and sensitivity over that found for P300s to classic, auditory oddball paradigms alone.