Figure 1. The experimental procedure.

On each trial two 50 ms tones, separated by an interval of 950 ms, were played and the participant was asked to respond which of the 2 tones was higher by pressing a button. Immediately after the button press, visual feedback in the form of a smiling face for correct answers, and a sad face for incorrect answers was presented for 300 ms. The inter-trial-interval was 700 ms.; The two frequencies were drawn from a wide distribution and their ratio was determined by a staircase paradigm (see Materials and Methods).