Effects of Spatial Attention on Visuocortical Processing: A Multi-Laboratory Replication of Clark & Hillyard (1996)

Whether selective attention alters initial sensory processing or instead only operates at higher cortical stages (often referred to as early vs. late selection) is a foundational question in cognitive neuroscience. Investigating the influence of covert visual selective attention, Clark and Hillyard (1996) found that directed attention modulated the amplitude of several early components (P1 and N1) of the visual event-related potential (ERP) derived from the ongoing electroencephalogram (EEG). However, attended and non-attended visual stimuli did not produce statistically different amplitudes in the C1 or P2 components. Dipole source estimation of the neural locus of these ERPs indicated that the C1 originated in primary (striate) visual cortex (V1), while the later components primarily arose from extrastriate visuocortical areas. Together, these results led to the conclusion that sustained spatial attention enhances the sensory gain of early visual processing in V1 via feedback projections from the extrastriate visual cortex where the P1 and N1 are generated. Despite the influential nature of this original work in EEG and cognitive neuroscience more broadly, recent research has reignited the debate on which stage of the visual processing hierarchy is influenced by attention. As part of the #EEGManyLabs project (Pavlov et al., 2021), we will be revisiting this issue by conducting a multi-site, high-powered direct replication of Clark and Hillyard (1996).