Fig. 1: Experimental paradigm and trial structure.
a Visual stimuli were presented one at a time in one of the four visual field quadrants. The locations were chosen to target opposite banks of the calcarine sulcus (CaS)35,127 where most of the human primary visual cortex (V1) is located. b Equivalent current dipoles in V1 for the stimulated locations in the upper (UVF) and the lower (LVF) visual field. Subtracting upper visual field potentials (vUVF) from lower visual field potentials (vLVF) produces the C1 difference wave (ΔC1), emphasizing retinotopic activity while eliminating non-retinotopic and/or common neural activity36,47. c Mean scalp topography of the ΔC1 in typically sighted controls, 50–100 ms after stimulus onset (n = 29). The topography, sign, and latency of the ΔC1 is consistent with a V1 origin34,35,52,128. d Trial structure. Participants saw brief circular grating patterns in one of the four quadrants or heard white noise bursts (150 ms) from the left or the right loudspeaker. The auditory and the visual stimuli were either presented alone (unimodal, e.g., left diagram) or together (audiovisual, AV). In AV trials, auditory and visual stimuli appeared either from the same side (spatially congruent, e.g., middle diagram), or opposite sides (spatially incongruent, e.g., right diagram). Participants detected rarely (20%) presented vertical oriented gratings, or a deviant sound of the same duration (not pictured). A uniformly distributed interstimulus interval between 1.5–2.2 s followed each stimulus.
