Capture of attention in selective frequency listening.

Four signal-detection experiments demonstrated robust stimulus-driven, or exogenous, attentional processes in selective frequency listening. Detection of just-above-threshold signal tones was consistently better when the, signal matched the frequency of an uninformative cue tone, even with relatively long cue-signal delays (Experiment 1) or when as few as 1 in 8 signals were at the cued frequency (Experiment 2). Experiments 3 and 4 compared performance with informative and uninformative cues. The involvement of intentional, or endogenous, processes was found to only slightly increase the size of the cuing effect beyond that evident with solely exogenous processes, although the attention band, a measure of how narrowly attention is focused, was found to be wider when cues were informative. The implications for models of auditory attention are discussed.

The time course of auditory segregation: concurrent vowels that vary in duration.

Human listeners perform well when identifying both members of simultaneous steady-state vowel pairs, even when the vowels start and stop at the same time, are presented monaurally, have approximately equal intensities, and have the same fundamental frequency (f0). The sensation described by listeners is of one dominant, vowel "colored" by the second, less easily identified, or nondominant vowel. Introducing a small separation in f0 between the vowels improves performance and listeners now report that there is a sensation of two voice sources rather than one. It has been suggested that listeners use an f0-guided segregation strategy in identifying two vowels that differ in f0. An experiment is reported in which four listeners attempted to identify both members of a pair of concurrent vowels which varied in duration from a single cycle of the stimulus waveform (one pitch period) up to eight cycles. A dominant vowel was identified with near 100% accuracy even in the single-cycle condition, whereas identification of the nondominant vowel showed a slow improvement up to eight cycles. A difference in f0 between the vowels improved identification of the nondominant vowel, but between three and four cycles of the vowels were necessary for this advantage. It is first concluded that the improvement in performance with stimulus duration is due to an improvement in identification of the nondominant vowel; and, second, a difference in f0 is not required for segregation of the dominant vowel which is available from stimuli which are too brief to provide a useful estimate of f0.

Effects of phase changes in low-numbered harmonics on the internal representation of complex sounds.

A series of experiments investigated the effect of phase changes in low-numbered single harmonics in target sounds that were either synthesized steady-state vowels fo periodic signals having only a single formant. A matching procedure was sued in which subjects selected a sound along a continuum differing in first formant frequency in order to get the best match with the target sound; perceptual effects of the phase manipulations in the target were detected as a change in the matched first formant frequency. Stimuli had to contain at least three harmonics to produce the effect, but id did not require a particular starting phase of the components. A suppression phenomenon is discussed, in which phase changes alter the phase-locking characteristics of auditory fibres tuned to low-numbered harmonics.