Fig. 4.

Recursive process generating a tonal auditory fractal. At each step of the recursive process, a new hierarchical level is added (in the figure, a lighter shade of gray) containing notes of a higher pitch and shorter duration. A certain note is dominant (e.g., Level 1) over a set of three notes (e.g., Level 2) if they occur simultaneously in the sequence (time-wise), and the former is of a lower pitch and longer duration. The pitch and rhythmical relations between dominant and subordinate elements are kept constant recursively across hierarchical levels. Thus, if the dominant level displays an ’ascending’ contour, so does the subordinate level. This between-level regularity occurs regarding the distance between levels, and distance within level (between notes of each set of three). In our recursion task, participants were first exposed to the first three iterations of the process, and then asked to discriminate between the fourth iteration and a foil (Fig. 5).