Effect of frequency ratio on infants' and adults' discrimination of simultaneous intervals

Effects of frequency ratio simplicity on infants' and adults' processing of simultaneous pitch intervals with component sine wave tones were tested. Both infants and adults showed superior performance at detecting a change from a perfect 5th (2:3) to either a tritone (32:45) or a minor 6th (5:8) interval than at detecting the reverse discriminations (minor 6th or tritone to perfect 5th). Similarly, both infants and adults showed superior performance at detecting a change from an octave (1:2) to either a major 7th (8:15) or a minor 9th (15:32) interval than at detecting the reverse discriminations. In combination with previous findings of infants' superior discrimination of tone sequences with prominent perfect 5th intervals, these results suggest that both simultaneous and sequential intervals with simple ratios are easy to process early in development.