What determines sustained visual attention? The impact of distracter positions, task difficulty and visual fields compared.

We quantified the interference of distracter stimuli on sustained visuo-spatial attention as a function of the distribution of attended positions in the visual fields (bilateral/unilateral, left/right, upper/lower), distracter positions (peripheral, between attended positions, between fixation and attended positions) and task difficulty. Compared to distinct distracter positions, bilateral field and lower field presentation had much stronger influence on the performance. Additionally, interactive effects between task difficulty and distracter position were found. This result was at variance with the previous models of visuo-spatial attention, which attached much more importance to the role of distracter positions compared to visual field effects. In directly comparing the impact of the abovementioned factors, the converse finding is evident-visual field effects, in particular bilateral presentations have a much stronger importance. Moreover, metaphoric concepts of attention like the "zoom lens" are not compatible with these results. The findings are discussed in the light of alternative models of sustained visuo-spatial attention. The visual system architecture and top-down mechanisms are considered.