Fig. 2

A staircase procedure for one representative subject in Exp I. The time course of the difference (Δ) between comparison and standard value recorded in Exp I across trials of a staircase procedure for Subject 7 at the high standard-value level (80%) for the three feedback conditions SND (top, blue), VIS (middle, red), and VIS + SND (bottom, green). The first 5 trials (grey underlay) reflect the reinforcement-learning phase. After that, wrong answers led to a 1% increase of the comparison stimulus, while two correct answers were needed for a 1% decrease (1 up/2 down staircase). The 10 reversals (indicated by an up-downward arrow) in the area between the vertical dashed lines (4th to 13th reversal) were used to calculate the JND, which is indicated by a horizontal dashed line. If the subject’s response was correct 7 times in a row at a 1% difference between comparison and standard stimulus, the JND was set to 1% and the run was terminated (see SND and VIS + SND)