Procedure.

Each participant was seated in a soundproof booth and performed the pitch discrimination task while their EEG was being recorded. Sound stimuli were presented using Presentation (Neurobehavioral Systems) through headphones, instructions were presented on a computer screen and participants responded by pressing keys on a computer keyboard. The experiment contained a training phase and an experimental phase. In the training phase, participants were first familiarized with the two pitch deviations by listening to tone pairs, with the tone being repeated either identically or with one of the two pitch deviations. Participants were then trained for the task with the 16 short melodies: participants judged whether the last two tones were identical or not by using a four-point scale (1: sure different / 2: not sure different / 3: not sure same / 4: sure same). No time limit was imposed for responses. Finally, participants were trained with the 8 example melodies. The experimental phase contained 6 blocks of the 48 melodies in a pseudo-random order (i.e., random orders with two constraints: the two melodies of a pair had to be separated by at least four melodies, and a given pitch deviation condition was not repeated more than five times in succession). Thus, participants judged a total of 288 melodies in the experimental phase. Participants received feedback on errors. To minimize contamination by motor processes, participants were instructed to avoid moving and blinking during the melody and to wait one imaginary beat after the end of the melody to respond. Participants had to press a key to proceed to the next trial and were told that they could relax and blink before proceeding to the next melodies.