Global-local orientation congruency effects in visual search

In a visual search task, subjects had to decide which of 2 possible target fetters was presented among 12 distracter letters. The 13 characters were arranged to form a global Navon-type letter. The global letter and the local letters (target and distracters) were independently presented in four different viewer-related orientations. When the global letter and the target were frequently congruently oriented, the response times increased with growing orientation disparity between them. This global-target congruency effect was independent from target identity (Experiment I), and it diminished when global and target orientations were not correlated (Experiment 2). The results indicate that the orientation of the global letter can be deliberately used in order to facilitate the processing of congruently oriented local targets. The alignment of a spatial frame of reference is discussed as the most probable process underlying this facilitation.