Automatic and voluntary orienting of attention in visual search: two independent processes?

Eighteen subjects performed two visual searchtasks, characterized by different cognitive load,which required to identify a vertical segmentbetween other segments, all with the same orientation,and a distractor that could be presented ornot. By varying the orientation of both targets anddistractors, it was manipulated the salience and thesimilarity between them, deemed considerable forbottom-up and top-down components respectively.Results showed a salience by similarity interaction,suggesting that, while in high cognitive loadconditions endogenous and exogenous components can act independently, when the task requires mildattentional resources, the two processes give rise toan interaction.