Volume 128, Issue 2, August 2010
Index of content:
- PSYCHOLOGICAL ACOUSTICS 
128(2010); http://dx.doi.org/10.1121/1.3458823View Description Hide Description
The present experiments examine the effect of a weak 40-ms tone burst (cue) on the detection of a closely following 40-ms signal at the same frequency. Detection becomes more difficult as the temporal separation (onset to onset) between them shortens from around 300 ms to under 52 ms. The threshold increase or proximal interference is similar whether signal frequency is constant from trial to trial—frequency certainty—or changing—frequency uncertainty. The increase is also similar whether the cue goes to the same ear as the signal or to the opposite ear. This contralateral interference by such weak cues, only 4 dB SL against a continuous broadband noise, appears to exclude a role for forward masking by the cues. When the preceding tone burst differs in frequency from the signal, threshold increases little at any temporal separation. Combined with earlier results on frequency uncertainty (Scharf, B., et al., 2007, J. Acoust. Soc. Am.121, 2149–2157), the present results show that a listener can shift focusing to an unexpected signal frequency in less than 52 ms. However, the rapidity of focusing is usually obscured by proximal interference, which possibly occurs whenever cue and signal share the same period of temporal integration.
128(2010); http://dx.doi.org/10.1121/1.3445786View Description Hide Description
Speech comprises dynamic and heterogeneous acoustic elements, yet it is heard as a single perceptual stream even when accompanied by other sounds. The relative contributions of grouping “primitives” and of speech-specific grouping factors to the perceptual coherence of speech are unclear, and the acoustical correlates of the latter remain unspecified. The parametric manipulations possible with simplified speech signals, such as sine-wave analogues, make them attractive stimuli to explore these issues. Given that the factors governing perceptual organization are generally revealed only where competition operates, the second-formant competitor (F2C) paradigm was used, in which the listener must resist competition to optimize recognition [Remez, R. E., et al. (Year: 1994). Psychol. Rev.101, 129–156]. Three-formant sine-wave analogues were derived from natural sentences and presented dichotically (one ; opposite ). Different versions of F2C were derived from F2 using separate manipulations of its amplitude and frequency contours. F2Cs with time-varying frequency contours were highly effective competitors, regardless of their amplitude characteristics. In contrast, F2Cs with constant frequency contours were completely ineffective. Competitor efficacy was not due to energetic masking of F3 by F2C. These findings indicate that modulation of the frequency, but not the amplitude, contour is critical for across-formant grouping.