Fig. 3.

Two examples (a–c and d–f) of the EEG-based orientation search (Subject 1). a,d The search outcome, i.e., the found optimal orientation is marked with a black cross. The acquired single-trial P20–N40 amplitudes are presented with black dots. The blue trace illustrates the final posterior mean curve (modelled behaviour of the response curve). b,e The progress of the estimated optimal orientation during the search run. The posterior mean curves computed based on the gathered P20–N40 responses are encoded with coloured rows (grey to blue), and the black crosses indicate the estimated optimal orientation (maximum of the posterior mean curve) on each iteration. The uppermost row (indicated with a black rectangle) correspond to the blue posterior mean curve in a and d. c,f The sampling order. After two randomly sampled orientations (with a 180° difference), we sampled the orientation where the knowledge-gradient function (grey-to-red-coloured rows) reached its maximum (black dots). (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)