Top-down effects operate quickly within occipital cortex.

A,C,D plot evoked potentials from occipital, central, and frontal electrodes marked by black, magenta, and orange circles in B. Blue/red trace shows waveform from electrodes ipsilateral/contralateral to probe location; green trace shows contralateral-minus-ipsilateral difference (shading shows ±2 SEM). Contour plots in B show interpolated scalp distribution of potential RMS for ipsilateral/contralateral waveforms (blue/red), as well as the ratio between contra-minus-ipsi waveform RMS and overall (ipsi + contra) RMS (green). E-F show the difference between rich and poor probe insertions for contra-minus-ipsi vaweform with respect to top-down (E) and bottom-up (F) maps, separately for the different electrodes (indexed on the y axis as pairs from which individual rows were computed), in the form of Z scores across participants. G plots RMS-normalized modulations (see Methods) in E/F on y/x axes pooled within black rectangles (occipital electrodes) in E/F, separately for different participants (1 symbol per participant, conventions similar to Fig 2F); solid symbols refer to intact scenes, open symbols to cut-out variant, blue symbols to results following artefact rejection (see Methods). H plots similar results from modulations pooled within magenta rectangles (central electrodes) in E/F; inset to H from modulations within orange rectangles (frontal electrodes). I-K plot the pooled quantities in G-H for specific comparisons on x- versus y-axes (top-down and bottom-up values are collated without distinction for this analysis): intact (undistorted) scenes versus cut-out variant (I); highpass/lowpass filtering of 1/20 Hz versus 0.5/40 Hz (J); values for intact scenes versus d′ log-ratios from Fig 2F (K). Ovals in I-K are aligned with best-fit line, with axes matched to 2 SD for values projected onto axes parallel/orthogonal to line. Data for this figure is available from S2 Data. EEG, electroencephalogram; RMS, root-mean-square; VEP, visual evoked potential.