[Level specific attention and dominance of global markers]

The global (i.e., highest) level of a hierarchically constructed stimulus pattern can often be identified faster than any subordinate level (Navon, 1977). This phenomenon was studied in two experiments aiming to confirm an attentional explanation of it. The hypothesis tested was that the reaction times for identifying each level of a three-level letter should be equal in a condition where valid level-specific cues are used. Experiment 1 provided results that show reduced differences between the reaction times for each level, but the differences were not reduced to near zero. The amount of interference in a condition with different letters on the level to be identified and the context levels was reduced substantially by using valid cues. One possible reason that the reaction time differences do not approach zero could be the nature of the stimulus onset produced by the imperative stimulus. This may cause attention to be automatically focused at the global level. By using a method that reduces this onset substantially, the efficiency of the level-specific cues was increased in Experiment 2. Attention was set at a certain level before stimulus presentation by identifying the first letter at a certain level in a double identification paradigm. This resulted in almost identical reaction times when attention was preset at the level to be identified. The strength of the level-specific attentional focusing depended strongly on the distinctness of the element's perceptual segregation at a certain level. This indicates that level-specific attentional selection, too, can be regarded as object-based.