ERP analysis
Analysis of P1, N1 and SPN was based on average amplitude across pre-registered spatiotemporal clusters. Electrodes were PO7, O1, O2 and PO8 (highlighted in Figure 1). P1 was defined as the maximum amplitude between 100 and 200 ms post stimulus onset in each participant and condition. N1 was the minimum between 150 and 250 ms. N1 drop was then computed as the difference from P1 peak. The SPN was computed as the difference between symmetry and random waves in the 200-1000 ms window. This was split into two sub-windows which differed in the pilot experiment (early 200-400 and late 400-1000). Oddball trails were not included in these analyses.
P300 was based on posterior central electrode cluster P1, PZ and P2 from 300-800 ms post stimulus onset. This was defined as the Oddball-Normal difference (averaging over symmetry and random trials).