The cognitive systems of attention can only process a fraction of available inputs and evolutionary advantage comes from perceiving what is most relevant in an environment. Accordingly, pre-attentive processing is a phase of perception in which the inputs that ultimately receive the full analysis of attention are automatically selected, based on relevance, from the wider field of information (Van der Heijden, 1996). In this area there are competing views regarding the extent to which emotionally charged stimuli, such as an angry face, can be processed preattentively. Some research has taken the view that emotionally charged stimuli are given high preference by perceptual systems to the extent that they can be processed rapidly, automatically and pre-attentively in their entirety (Pessoa & Adolphs, 2010). Neurologically, a specialized sub-cortical path of information processing that is direct to the amygdala has been proposed, perhaps as an adaptation driven by the survival value inherent in perceiving emotional stimuli such as threatening facial expressions (LeDoux, 2003).
In one research example, participants focused their attention on either a pair of pictures, left and right or above and below, a central fixation (Vuilleumier, Armony, Driver, & Dolan, 2001). For the target pair, participants decided whether the two houses or faces shown were the same or different. The faces either had a neutral or fearful expression. While the matching occupied attention, faces or houses continued to be shown as an irrelevant pair in the other spaces. The results obtained via fMRI showed that activation of the fusiform gyrus was greatly affected by whether or not the participant was attending to the face (Vuilleumier et al., 2001). However, activation of the left amygdala to fearful faces persisted even in the unattended condition. Thus, the researchers concluded that emotion influences face processing so that it is independent of attention.
