Prefrontal Cognitive Controls On Selective Attention

The ability to remain focused on goal-relevant stimuli in the presence of potentially interfering distractors is crucial for our cognition. However, we are much easier to be distracted by goal irrelevant information than we could imagine. The exact mechanisms through which people could ignore distractors are still in a hot debate. Recently, Lavie proposed two different mechanisms for distractor rejection(Lavie, 2005). The first is a passive one, increasing perceptual load in the relevant task may exhaust perceptual capacities, and the lack of resources results in decreased or diminished processing of distractor. There had been numerous evidences supporting this passive mechanism of selection. However, such a passive way in itself is not powerful enough to completely eradicate distractions, since our brain always leave some resources available to perceive the distractors, especially in situations of low perceptual load. The irrelevant information can thus penetrate our perception and interferes in our behaviors. Fortunately, there also exists a top-down cognitive control mechanism that can actively reject distractions. It has long been implicated that cognitive control functions mediated by prefrontal cortex may play a key role in such an active control mechanism. However, direct empirical evidence is still sparse. In order to further demonstrate this top-down active control mechanism, I carried out a series of studies. Study one used EEG (a high temporal resolution technique) to investigate the temporal dynamics of cognitive controls on acoustic distractor processing. The mismatch negativity (MMN) which serves as an index to the early detection of irrelevant changes, increased with cognitive control load, suggesting that at the early stages of distractor processing, high-level cognitive resources are required to suppress the detection of task-irrelevant changes. In contrast to the MMN, the P3a component which indicates the involuntary orienting of attention to distraction, decreased with load, suggesting that at the later stages of processing the same cognitive resources are needed for orienting of attention to the task-irrelevant but salient events. These findings complements Lavie's load theory of selective attention and together presents a more complete picture of the early- and late-selection...