ERP signs of frontal and occipital processing of visual targets and distractors within and without the channel of spatial attention

ABTRACT Available neurophysiological and neuroimaging studies support the view that attentional processing is carried out by means of the reciprocal communications between distributed neural networks of brain areas including frontal and prefrontal cortex, as well as the occipital-temporal-parietal cortices. In this study ERPs were recorded using a 32 channels whole-head montage while volunteers performed conjoined selection tasks of spatial location and spatial frequency. Target stimuli and distractors were presented within and without attended locations. The data indicate that during spatially directed selective processing, the visual system, although overall increasing processing activation for all stimuli falling within the attended channel of attention, treats the relevant and irrelevant sources of information differently. They also suggest that this occurs not only within the relevant channel of attention, but without it too. Indeed, the present findings suggest that, while enhancing processing of frequency-relevant gratings with respect to frequencyirrelevant ones since the earliest sensory level, as reflected by C1, at the attended location, the system seems also actively to suppress the processing of the latter stimuli with respect to the former ones at the neglected location, already starting at early sensory level, as reflected by P1. As for the prefrontal cortex, ERPs data and their topography suggested that distinct sub-regions of the latter might serve distinct attention functions. In fact, while dorsolateral regions would control the orienting of attention toward relevant space locations, the left-hemisphere inferior posterior prefrontal cortex (PFC) may suppress processing of distractors within an attended channel. Conversely, the dorsal frontal-polar PFC might boost, though in different degrees, the post-perceptual/semantic processing of relevant information by posterior brain areas independent of location relevance.