Contralateral influences of wideband inhibition on the effect of onset asynchrony as a cue for auditory grouping

Onset asynchrony is an important cue for segregating sound mixtures. A harmonic of a vowel that begins before the other components contributes less to vowel quality. This asynchrony effect can be partly reversed by accompanying the leading portion of the harmonic with an octave-higher captor tone. The original interpretation was that the captor and leading portion formed a perceptual group, but it has recently been shown that the captor effect depends on neither a common onset time nor harmonic relations with the leading portion. Instead, it has been proposed that the captor effect depends on wideband inhibition in the central auditory system. Physiological evidence suggests that such inhibition occurs both within and across ears. Experiment 1 compared the efficacy of a pure-tone captor presented in the same or opposite ear to the vowel and leading harmonic. Contralateral presentation was at least as effective as ipsilateral presentation. Experiment 2 used multicomponent captors in a more comprehensive evaluation of harmonic influences on captor efficacy. Three captors with different fundamental frequencies were used, one of which formed a consecutive harmonic series with the leading harmonic. All captors were equally effective, irrespective of the harmonic relationship. These findings support and refine the inhibitory account. © 2007 Acoustical Society of America.

Grouping and the pitch of a mistuned fundamental component:effects of applying simultaneous multiple mistunings to the other harmonics

Mistuning a harmonic produces an exaggerated change in its pitch. This occurs because the component becomes inconsistent with the regular pattern that causes the other harmonics (constituting the spectral frame) to integrate perceptually. These pitch shifts were measured when the fundamental (F0) component of a complex tone (nominal F0 frequency = 200 Hz) was mistuned by +8% and -8%. The pitch-shift gradient was defined as the difference between these values and its magnitude was used as a measure of frame integration. An independent and random perturbation (spectral jitter) was applied simultaneously to most or all of the frame components. The gradient magnitude declined gradually as the degree of jitter increased from 0% to ±40% of F0. The component adjacent to the mistuned target made the largest contribution to the gradient, but more distant components also contributed. The stimuli were passed through an auditory model, and the exponential height of the F0-period peak in the averaged summary autocorrelation function correlated well with the gradient magnitude. The fit improved when the weighting on more distant channels was attenuated by a factor of three per octave. The results are consistent with a grouping mechanism that computes a weighted average of periodicity strength across several components. © 2006 Elsevier B.V. All rights reserved.

Asynchrony and the grouping of vowel components:captor tones revisited

Asynchrony is an important grouping cue for separating sound mixtures. A harmonic incremented in level makes a reduced contribution to vowel timbre when it begins before the other components. This contribution can be partly restored by adding a captor tone in synchrony with, and one octave above, the leading portion of the incremented harmonic [Darwin and Sutherland, Q. J. Exp. Psychol. A 36, 193-208 (1984)]. The captor is too remote to evoke adaptation in peripheral channels tuned to the incremented harmonic, and so the restoration effect is usually attributed to the grouping of the leading portion with the captor. However, results are presented that contradict this interpretation. Captor efficacy does not depend on a common onset, or harmonic relations, with the leading component. Rather, captor efficacy is influenced by frequency separation, and extends to about 1.5 oct above the leading component. Below this cutoff, the captor effect is equivalent to attenuating the leading portion of the incremented harmonic by about 6 dB. These results indicate that high-level grouping does not govern the captor effect. Instead, it is proposed that the partial restoration of the contribution of an asynchronous component to vowel timbre depends on broadband inhibition within the central auditory system. © 2006 Acoustical Society of America.

Remote facilitation in the Fourier domain

To explore spatial interactions between visual mechanisms in the Fourier domain we measured detection thresholds for vertical and horizontal sine-wave gratings (4.4 deg diameter) over a range of spatial frequencies (0.5-23 c/deg) in the presence of grating and plaid masks with component contrasts of 8%, orientations of ±45° and a spatial frequency of 1 c/deg. The mask suppressed the target grating over a range of ±1 octave, and the plaid produced more suppression than the grating, consistent with summation of mask components in a broadly tuned contrast gain pool. At greater differences in spatial frequency (∼3 octaves), the plaid and grating masks both produced about 3 dB of facilitation (they reduced detection thresholds by a factor of about √2). At yet further distances (∼4 octaves) the masks had no effect. The facilitation cannot be attributed to a reduction of uncertainty by the mask because (a) it occurs for mask components that have very different spatial frequencies and orientations from the test and (b) the large stimulus size and central fixation point mean there was no spatial uncertainty that could be reduced. We suggest the results are due to long-range sensory interactions (in the Fourier domain) between mask and test-channels. The effects could be due to either direct facilitation or disinhibition. © 2006 Elsevier Ltd. All rights reserved.

The influence of adaptation and inhibition on the effects of onset asynchrony on auditory grouping

Onset asynchrony is an important cue for auditory scene analysis. For example, a harmonic of a vowel that begins before the other components contributes less to the perceived phonetic quality. This effect was thought primarily to involve high-level grouping processes, because the contribution can be partly restored by accompanying the leading portion of the harmonic (precursor) with a synchronous captor tone an octave higher, and hence too remote to influence adaptation of the auditory-nerve response to that harmonic. However, recent work suggests that this restoration effect arises instead from inhibitory interactions relatively early in central auditory processing. The experiments reported here have reevaluated the role of adaptation in grouping by onset asynchrony and explored further the inhibitory account of the restoration effect. Varying the frequency of the precursor in the range ± 10% relative to the vowel harmonic (Experiment 1), or introducing a silent interval from 0 to 320 ms between the precursor and the vowel (Experiment 2), both produce effects on vowel quality consistent with those predicted from peripheral adaptation or recovery from it. However, there were some listeners for whom even the smallest gap largely eliminated the effect of the precursor. Consistent with the inhibitory account of the restoration effect, a contralateral pure tone whose frequency is close to that of the precursor is highly effective at restoring the contribution of the asynchronous harmonic (Experiment 3). When the frequencies match, lateralization cues arising from binaural fusion of the precursor and contralateral tone may also contribute to this restoration. (PsycINFO Database Record (c) 2012 APA, all rights reserved)

The verbal transformation effect and the perceptual organization of speech:influence of formant transitions and F0-contour continuity

This study explored the role of formant transitions and F0-contour continuity in binding together speech sounds into a coherent stream. Listening to a repeating recorded word produces verbal transformations to different forms; stream segregation contributes to this effect and so it can be used to measure changes in perceptual coherence. In experiment 1, monosyllables with strong formant transitions between the initial consonant and following vowel were monotonized; each monosyllable was paired with a weak-transitions counterpart. Further stimuli were derived by replacing the consonant-vowel transitions with samples from adjacent steady portions. Each stimulus was concatenated into a 3-min-long sequence. Listeners only reported more forms in the transitions-removed condition for strong-transitions words, for which formant-frequency discontinuities were substantial. In experiment 2, the F0 contour of all-voiced monosyllables was shaped to follow a rising or falling pattern, spanning one octave. Consecutive tokens either had the same contour, giving an abrupt F0 change between each token, or alternated, giving a continuous contour. Discontinuous sequences caused more transformations and forms, and shorter times to the first transformation. Overall, these findings support the notion that continuity cues provided by formant transitions and the F0 contour play an important role in maintaining the perceptual coherence of speech.