Fig. 1

General procedure, stimuli and FT-EEG paradigm. (a) Participants’ neural and behavioral discrimination sensitivity was assessed before and after explicit categorization training. (b) Stimuli (used for this assessment) consisted out of shapes varying across seven steps along one (i.e., the assigned) of two dimensions: aspect-ratio (AR i.e., the width-to-height ratio) and curvature (CR i.e., the degree to which a curve deviates from a straight line). The category boundary for the assigned dimension was introduced at the midpoint of the dimension (i.e., 0%: fourth stimulus) during the explicit categorization training. To look at behavioral discrimination sensitivity across the assigned stimulus dimension, we compared perceptual discrimination of stimulus pairs within (i.e., pair 1–3 and pair 5–7) and between the trained category (i.e., pair 3–5). (c) For the neural discrimination sensitivity assessment, we used an FT-EEG sweep paradigm, which was swept for the oddball stimuli across the assigned stimulus dimension (e.g., curvature) while the base stimulus stayed the same (i.e., one of the end-points, in this example is the 99% curved). To compare neural discrimination sensitivity along the stimulus dimension, we specifically looked at the FT-EEG baseline-subtracted oddball amplitude of stimuli at sweep step 2 and 6 to assess neural sensitivity within the category and of stimuli at sweep step 4 for neural sensitivity across the trained category boundary