Experimental design

Participants were requested to minimize movement throughout the experiment, except during breaks between blocks. No particular instructions were given with respect to when to blink, as eye blink artefacts can be removed using independent component analysis (ICA; Delorme and Makeig, 2004; Chaumon et al., 2015).

Experiments followed an Oddball design, divided in 13 blocks with an average duration of 3.3 min each. During each block, a total of 98 pseudowords were presented, with an inter stimulus interval that varied between 900 and 1300 ms. During the first of such blocks, only STD pseudowords were presented. Subsequently, participants completed 12 blocks composed of 84% Standard pseudowords 8% XYY deviant pseudowords and 8% XXY deviant pseudowords. Within each block, pseudoword order was pseudo-random. A minimum of two and a maximum of four STD pseudowords were presented between deviants and no deviants were presented more than two times consecutively (Fig. 1C).

In experiment 1, participants were instructed to learn all made up “words” (i.e., pseudowords) in block one, and from block 2 onwards count the occurrence of “mistaken words” (i.e., deviant pseudowords) and write down the number of mistaken words during the pauses between blocks.

In experiment 2, participants were not informed about the presence of deviants and were simply instructed to learn all made up words (i.e., pseudowords). To ensure that the participant would pay attention during the experiment, they were informed that they would be subject to a test after the word learning task. After listening to the blocks of pseudowords, behavioral performance was assessed, by means of a forced choice test. On each trial, participants heard two pseudowords in sequence and were requested to choose the one that most likely was presented during the experiment. Participants completed four trials for each of six contrasts between conditions, for a total of 24 trials, presented in pseudorandom order (only 1 repetition of contrast type was allowed). The contrasts between conditions were “STD versus XYY,” “STD versus XXY,” “XYY versus XXY,” “STD versus NEW,” “XYY versus NEW,” and “XXY versus NEW.” Participants reported their answers verbally and the experimenter entered them through keyboard. Order of presentation of pseudowords within trial was counterbalanced.