The time-course of global and local attentional guidance in Kanizsa-figure detection.

Object configurations can be perceptually represented at various hierarchical levels. For example, in visual search, global Kanizsa figures are detected efficiently, whereas search for local groupings is inefficient, with similarity-dependent nontarget interference arising at the hierarchical level that defines the target (Conci, Müller, & Elliott, 2007). The present study was designed to examine the electrophysiological correlates of this global-local search asymmetry. The results revealed differences between hierarchical object levels to be evident throughout a number of processing stages: search for a global, versus a local, target elicited larger amplitudes in early sensory components (P1, N1). Moreover, the efficiency of attentional orienting towards a target was mirrored in the Posterior Contralateral Negativity (PCN), with PCN latencies being substantially delayed (by ∼ 70 ms) with local, versus global, targets. Finally, late components (P3 and slow wave--SW) reflected the overall search efficiency, which was determined by both the hierarchical level at which the target was defined and the similarity-based nontarget interference. Taken together, this pattern shows that multiple, sequential processes of object completion contribute to the attentional precedence of a globally bound object over a mere local element grouping.