Priming of attention to local or global levels of visual analysis

Humans can shift attention between parts and wholes, as shown in experiments with complex hierarchical stimuli, such as larger, global letters constructed from smaller, local letters. In these experiments, a target stimulus appears at either the local or the global level, with a distractor at the other level. A shift of attention between levels is said to be demonstrated through a form of priming, whereby targets at one level are presented with a higher probability than at the other level. This base-rate type of priming can facilitate speed of responding to targets, as seen in shorter reaction times to targets at the primed level. Experiment 1 demonstrated such a priming effect in pigeons. Experiment 2 confirmed this priming, by showing that accuracy remained high for familiar targets, at either level, even when distractors at the other level were novel.