Identification of microtonal melodies: effects of scale-step size, serial order, and training

The perception of microtonal scales was investigated in a melodic identification task. In each trial, eight pure tones, equally-spaced in log frequency in the vicinity of 700 Hz, were presented in one of nine different serial orders. There were two experiments, each with 108 trials (six scales [tone sets] x nine serial orders x two repetitions). In each experiment, 30 subjects, half of whom were musically trained, were asked to match each melody to one of 9 visual representation (frequency-time grids). In Experiment 1, the six scales were spaced at intervals of 25, 33, 50, 67, 100, and 133 cents (100 cents = 1 semitone approximately 6% of frequency). Performance was worse for scale steps of 25 and 33 cents than it was for wider scale steps. There were no significant effects at other intervals, including the interval of 100 cents, implying that melodic pattern identification is unaffected by long-term experience of music in 12-tone equally tempered tuning (e.g., piano music). In Experiment 2, the six scales were spaced at smaller intervals, of 10, 20, 30, 40, 50, and 60 cents. Performance for the three narrower scale steps was worse than that for the three wider scale steps. For some orders, performance for the narrowest scale step (10 cents) did not exceed chance. The smallest practical scale step for short microtonal melodies in a pattern-identification task was estimated as being 10-20 cents for chance performance, and 30-40 cents for asymptotic performance.