Perception of concurrent vowels: The effect of varying their relative level

Abstract When identifying pairs of simultaneous steady-state vowels, listeners perform well even when the two vowels start and stop at the same time, are presented monaurally, have the same fundamental frequency ( f 0 ), and have approximately equal intensities. The sensation described by listeners is of one dominant vowel “coloured” by a second or non-dominant vowel. A small difference in f 0 improves performance and typically results in a sensation of two voice sources rather than of one voice coloured by another. An experiment is reported in which four listeners attempted to identify separately the dominant and the non-dominant vowel when the relative levels of the vowels were varied over a 28 dB range and the vowels had either the same f 0 or different f 0 s. As in previous experiments, performance improved when there was an f 0 difference between the vowels, but this advantage was reduced though not abolished when the f 0 separation was one octave. This advantage of f 0 separation was seen almost entirely in increased identification of the non-dominant vowel and was apparent at all but the greatest relative level differences tested. Finally, there were clear differences in the pattern of vowel dominance across the different vowel combinations, with subjects showing broadly similar patterns. Dominance may reflect cognitive “decision” strategies in addition to spectral masking at the level of the peripheral auditory system.