The direct octaves rule: Testing a scene-analysis interpretation

A venerable rule of traditional Western part writing is the so-called Direct Octaves Rule (also known as Hidden or Exposed octaves), whereby similar pitch motion (i.e., two or more voices moving in the same direction) to a perfect octave should be avoided unless step motion is used. A number of interpretations have been offered as to why musicians might follow this rule. A traditional account (Fux, 1725/1966) exhibits several inconsistencies. A modern interpretation based on auditory scene analysis appears to have merit. However, this interpretation has yet to be tested empirically. Three experiments test the scene-analysis account using numerosity judgments for complex chords as the dependent measure. In Experiment 1, musician listeners show decreasing accuracy in numerosity judgments when an octave is present in the sonority – as predicted. In experiments 2 and 3, chords were preceded by a single neighboring or distant tone. It was hypothesized that neighboring primes would increase the accuracy of numerosity judgments for octave-containing chords more than distant primes – consistent with the Direct Octaves rule. However, no such facilitation was observed. Nevertheless, a post-hoc test showed improved accuracy when the octave was approached by step motion in highest voice compared with step-approach to the lowest voice. This latter finding is consistent with the most restrictive formulations of the direct octaves rule.