FRONTAL PROCESSING NEGATIVITY IN A VISUAL SELECTIVE ATTENTION TASK

The auditory processing negativity has been associated with the mainte nance of an internal representation of context and has been shown to b e dependent on the integrity of the prefrontal cortex. Previous visual selective attention studies have failed to show consistent evidence o f a frontal processing negativity. The present study employed a multi- dimensional visual selective attention task, modelled after Hillyard a nd Mante (Percept. Psychophys., 1984, 36: 185-198). Subjects responded to infrequent target stimuli of a particular location, color and heig ht combination, while ignoring all stimuli differing from the target o n any of these dimensions. Consistent with previous literature, at pos terior 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. Ho wever, unlike previous studies, a large prolonged processing negativit y was evident at all frontal sites. This effect involved three compone nts, an early frontally negative component peaking around the N1, a fr ontocentral negativity maximal at 300 ms and a long-lasting widespread negativity beginning after 500 ms. Processing of location preceded th e onset of color and location/color conjunction processing, suggesting hierarchical stimulus feature analysis. However, at posterior tempora l sites there was evidence of parallel color processing in the unatten ded location.