Stimuli and trial sequence. A) Shapes used for the morphing delayed match-to-sample task. Complex shapes: (S) 1 to 10; simple circle shape (S) 11. B) Trial sequence: A static target was presented for 2.4 s and subsequently started to continuously change its contours and morphed with a smooth motion into another of the predefined shapes. The initial target shape reappeared after 3, 6, 9 or 12 s, and the participants had to indicate the recognition of the target shape by a button press. After complete presentation of the target shape, the sequence morphed into one other shape in order to prevent trial termination with the target.