Early and Late Mechanisms of Object-Based Attention: Dissociation Between Faces and Non-Face Objects.

The object-based attention (OBA) effect has been consistently observed across various objects using the double-rectangle paradigm, but its relevance to faces has sparked controversy. To address this issue, we used the event-related potentials (ERP) technique to examine the temporal dynamics of object processing and its impact on the OBA effect. Behavioral data revealed the presence of the OBA effect for non-face mosaic objects but not for faces. After correcting for attentional horizontal-vertical symmetry, we identified two ERP components associated with the OBA mechanisms: corrected N1 and Late Positive Deflection (LPD). The corrected N1 exhibited a larger amplitude in within-object compared to between-object conditions, regardless of whether faces or non-face objects were presented. In contrast, the corrected LPD showed a larger amplitude in between-object relative to within-object conditions, exclusively for non-face objects. These findings suggest that the corrected N1 and LPD reflect different stages of the OBA mechanism. The early object-based N1 component may reflect the processing of coarse perceptual entities, without detailed object information. In contrast, the later object-based LPD component suggests a more integrated processing of objects with detailed information, where two faces are perceived as a unified whole due to their inherent social connections. This distinction between early and late mechanisms of OBA provides new insights into how attention selected two faces as either integrated or separate operational units.