The improvement of identification accuracy of concurrent vowels with differences in fundamental frequency ([DELTA]F0) is usually
attributed to mecanisms that exploit harmonic structure. To decide whether identification is aided primarily by the harmonic
structure of the target ("harmonic enhancement") or that of the ground ("harmonic cancellation"), pairs of synthetic vowels, each of
which was either harmonic or inharmonic, were presented to listeners for identification. Responses for each vowel were scored
according to the vowel's harmonicity, the harmonicity of the vowel that accompanied it, and [DELTA]F0. For a given target, identification
was better by about 3% for a harmonic ground unless the target was also harmonic with the same F0. This supports the cancellation
hypothesis. Identification was worse for harmonic than for inharmonic targets by 3-8%. This does not support the enhancement
hypothesis. When both vowels were harmonic, identification was better by about 6% when the F0s differed by 1/2 semitone.
However, when at least one vowel was inharmonic, [DELTA]F0 had no significant effect. Identification of constituents of pairs was
generally not the same when the target was harmonic and the ground inharmonic or vice-versa. Results are interpreted in terms of
harmonic enhancement and harmonic cancellation, and alternative explanations such as phase effects are considered.