Dissociation of pitch from timbre in auditory short-term memory

In three experiments, untrained listeners made same/different judgments on pairs of pure or complex tones with periods that eventually differed by +/- 4%. On each trial, the two test tones were separated by 4.3 s, during which other tones (I) were heard but had to be ignored. The period (p) of the first test tone was randomly selected between 1/600 and 1/300 s. The period of each I tone was randomly selected among four possible values, close to p (+/- 3% or 6% apart) in some conditions, and remote from p in other conditions. In addition, from condition to condition, the spectral content of the I tones was varied independently of their periods: The I tones could have the same harmonic content as the test tones, or a very different harmonic content. Subjects' performances were much better when the periods of the I tones were remote from p than when they were close to p, as expected from previous findings by D. Deutsch [e.g., Science 175, 1020-1022 (1972)]. But, more importantly, the relation between the spectral contents of the I tones and the test tones had, by itself, practically no effect on performance. Thus performance was affected by the pitches of the I tones, but not by their timbres. These results suggest that pitch is processed independently of timbre in auditory short-term memory.