Differentiating spatial and object-based effects on attention: An event-related brain potential study with peripheral cueing

Do spatial attention and object attention modulate visual processing in similar ways? Previously we have found a dissociation between these two forms of attention on ERP measures of sensory processing under conditions of peripheral cueing, with spatial attention effects associated with changes over anterior scalp regions and object attention effects associated with changes over posterior regions (He, X., Fan, S., Zhou, K., Chen, L., 2004. Cue validity and object-based attention. J. Cogn. Neurosci. 16, 1085-1097). However, under conditions of central cueing recent data suggest that spatial and object attention have similar effects over posterior cortical areas (e.g., Martínez, A., Teder-Sälejärvi, W., Hillyard, S.A., 2007. Spatial attention facilitates selection of illusory objects: evidence from event-related brain potentials. Brain Res. 1139, 143-152). In the present study we present further evidence for dissociation between spatial and object-based attention under conditions in which spatial attention effects were enhanced by increasing the cue validity and the task load. The data replicated our previous results, with the effects of spatial attention found in an enhanced anterior N1, while the effects of object-based attention emerged in an enhanced posterior N1. Analyses of attention effect maps and current source density maps confirmed the distinct scalp distributions. These results support the proposal that, under peripheral cueing, spatial attention and object attention are associated with activity respectively in anterior and posterior brain structures, and further suggest a distinction between how attention modulates processing under conditions of central cueing and peripheral cueing.