Pitches of concurrent vowels

When two vowels are presented simultaneously, listeners can report their phonemic identities more accurately if their fundamental frequencies (F-o's) are different rather than the same. If the F-o difference (Delta F-o) is large, listeners hear two vowels on different pitches; if the Delta F-o is small the vowels are identified less accurately and they do not evoke different pitches. The present study used a matching task to obtain judgments of the pitches evoked by "double vowels" created from pairwise combinations of steady-state synthetic vowels /i/, /a/, /u/, /ae/, and /(sic)/. One F-o was always 100 Hz; the other F-o was either 0, 0.25, 0.5, 1, 2, or 4 semitones higher. Experienced listeners adjusted the F-o of a tone complex to assign pitch matches to 50-ms or 200-ms double vowels. For Delta F-o's up to two semitones, listeners' matches formed a single cluster in the frequency region spanned by the two F-o's. When the Delta F-o was 4 semitones, the matches generally formed two clusters close to the F-o of each vowel, suggesting that listeners perceive two distinct pitches when the Delta F-o is 4 semitones but only one clear pitch (possibly accompanied by one or more weaker pitches) with smaller Delta F-o's. When the duration was reduced from 200 ms to 50 ms, only a subset of the vowel pairs with a Delta F-o of 4 semitones produced a bimodal distribution of matches. In general, 50-ms stimuli were matched less consistently than their 200-ms counterparts, indicating that the pitches of concurrent vowels emerge less clearly when the stimuli are brief. Comparisons of pitch and vowel identification data revealed a moderate correlation between match intervals (defined as the absolute frequency difference between first and second pitch matches) and identification accuracy for the 200-ms stimuli with the largest Delta F-o of 4 semitones. The link between match intervals and vowel identification was weak or absent in conditions where the stimuli evoked only one pitch. (C) 1998 Acoustical Society of America. [S0001-4966(98)05702-6].