Frontal processing negativity in a visual selective attention task.

The auditory processing negativity has been associated with the maintenance of an internal representation of context and has been shown to be dependent on the integrity of the prefrontal cortex. Previous visual selective attention studies have failed to show consistent evidence of a frontal processing negativity. The present study employed a multi-dimensional visual selective attention task, modelled after Hillyard and Munte (Percept. Psychophys., 1984, 36: 185-198). Subjects responded to infrequent target stimuli of a particular location, color and height combination, while ignoring all stimuli differing from the target on any of these dimensions. Consistent with previous literature, at posterior sites, location selection resulted in enhancement of P1 and N1 amplitude, followed by color selection within the attended location at around 200 ms. These effects were most pronounced contralaterally. However, unlike previous studies, a large prolonged processing negativity was evident at all frontal sites. This effect involved three components, an early frontally negative component peaking around the N1, a frontocentral negativity maximal at 300 ms and a long-lasting widespread negativity beginning after 500 ms. Processing of location preceded the onset of color and location/color conjunction processing, suggesting hierarchical stimulus feature analysis. However, at posterior temporal sites there was evidence of parallel color processing in the unattended location.