Intonation sensitivity for traditional and nontraditional chords

We studied listeners' intonation sensitivity to traditional (major and minor) and nontraditional chords. The nontraditional chords have frequency ratios of 3:5:7 and 5:7:9 and, like the major chord, have coincident upper partials and unambiguous fundamental basses. The center tone only of each of these four triads was varied from its just (integer ratio) value by -30, -15, 0, +15, and +30 cents. Each tone had ten partials whose amplitudes decreased with frequency relative to the fundamental (9 dB per octave). Subjects judged which chord (or chordal sequence) of a pair was more in tune, smooth and/or pleasant. Listeners' intonation sensitivity curves exhibited regular patterns for both traditional and nontraditional chords. However, our subjects divided into two groups: One group preferred chords in just intonation and their preferences decreased monotonically as the intonation deviated from just intonation; the other group preferred intonations that deviated from just intonation by +/- 15 cents.