Experimental design of behavioural and EEG sessions.

A) An example trial for the audiovisual condition in the behavioural session. Each trial consisted of a (centred) reference stimulus and a target stimulus presented at one of eight locations along the horizontal meridian of the display. B) An example trial for the audiovisual condition in the EEG session. The top row displays the possible locations of stimuli. In each trial, participants were presented with 20 stimuli that were each spatially localised to one of five possible locations along the horizontal meridian. The task was to determine if there were more stimuli presented to the left or right of fixation.

Behavioural performance is improved for audiovisual stimuli.

A) Average accuracy of responses across participants in the behavioural session at each stimulus location for each stimulus condition fitted to a psychometric curve. Steeper curves indicate greater sensitivity in identifying stimulus location. B) Average sensitivity across participants, estimated from psychometric curves, for each stimulus condition. The red cross indicates estimated performance assuming optimal (MLE) integration of unisensory cues. C) Average sensitivity across participants in the EEG session for each stimulus condition. Error bars indicate ±1 SEM.

Audiovisual ERPs follow an additive principle.

Average ERP amplitude for each modality condition. Five plots represent the different stimulus locations, as indicated by the grey inset, and the final plot (bottom-right) shows the difference between the summed auditory and visual responses and the audiovisual response. Shaded error bars indicate ±1 SEM. Coloured horizontal bars indicate cluster corrected periods of significant difference between visual and audiovisual ERP amplitudes.

Spatiotemporal representation of audiovisual location.

A) Accuracy of locations decoded from neural responses for each stimulus condition. Shaded error bars indicate ±1 SEM. Coloured horizontal bars indicate cluster corrected periods that showed a significant difference from chance (0). B) Topographic decoding performance in each condition during critical period (grey inset in (A)).

Super-additive multisensory interaction in multivariate patterns of EEG activity.

A) Decoding sensitivity in each stimulus condition across the epoch. Overall trends closely matched decoding accuracy. B) Predicted (MLE and aggregate A+V) and actual audiovisual sensitivity across the epoch. Coloured horizontal bars indicate cluster corrected periods where actual sensitivity significantly exceeded that which was predicted. Shaded error bars indicate ±1 SEM.

Audiovisual decoding sensitivity is significantly positively correlated to behavioural sensitivity.

The correlations (Spearman’s Rho) between decoding and behavioural sensitivity from the EEG session from 150-250 ms post-stimulus onset for each stimulus condition, with a line of best fit.