Temporal effects in masking and their influence on psychophysical tuning curves

Psychophysical tuning curves (PTCs) were obtained in simultaneous and forward masking for a 20-ms, 1000-Hz signal presented at 10 dB SL. The signal was presented at the beginning of, at the temporal center of, at the end of, or immediately following a 400-ms masker. The first experiment was done in quiet; the second experiment was done in the presence of two bands of noise on either side of 1000 Hz. The results were similar in quiet and in noise. In simultaneous masking, the PTCs were broadest for the signal at masker onset, and generally sharpest for the signal at temporal center; the differences were largest on the high-frequency side. In most cases, there was virtually no difference in Q10 between the forward-masking PTC and the simultaneous-masking PTC with the signal temporally centered, although the high-frequency slope was always steeper in forward masking. These results indicate that, at least for brief signals, frequency selectivity measured with simultaneous-masking PTCs and the degree of sharpening revealed in forward-masking PTCs depend upon the temporal position of the signal within the simultaneous masker.     

Integrating over Higgs Branches

We develop some useful techniques for integrating over Higgs branches in supersymmetric theories with 4 and 8 supercharges. In particular, we define a regularized volume for hyperk?hler quotients. We evaluate this volume for certain ALE and ALF spaces in terms of the hyperk?hler periods. We also reduce these volumes for a large class of hyperk?hler quotients to simpler integrals. These quotients include complex coadjoint orbits, instanton moduli spaces on ℝ⁴ and ALE manifolds, Hitchin spaces, and moduli spaces of (parabolic) Higgs bundles on Riemann surfaces. In the case of Hitchin spaces the evaluation of the volume reduces to a summation over solutions of Bethe Ansatz equations for the non-linear Schr?dinger system. We discuss some applications of our results. Received: 2 May 1999/ Accepted: 16 July 1999     

A preliminary study of particle velocity during phonation in an in vivo canine model

The particle velocity across the glottis was measured with simultaneous electroglottography, photoglottography, and subglottic pressure in an in vivo canine model of phonation. A constant temperature anemometer measured flow velocity at five midline anterior to posterior glottal positions. Tracheal input air flow was varied in five steps from 175 to 500 cc/s, while vocal fold approximation was achieved by constant electrical stimulation of the laryngeal nerves. For all levels of air flow, a decreasing peak velocity gradient was observed from the anterior commissure to the arytenoids. Time-varying features of the flow velocity are discussed in relation to glottal vibratory events and aerodynamics.     

Comodulation masking release as a function of bandwidth and time delay between on-frequency and flanking-band maskers

The threshold for a signal masked by a narrow band of noise centered at the signal frequency (the on-frequency band) may be reduced by adding to the masker a second band of noise (the flanking band) whose envelope is correlated with that of the first band, an effect called comodulation masking release (CMR). This paper examines CMR as a function of masker bandwidth and time delay between the envelopes of the on-frequency and flanking bands. The 1.0-kHz sinusoidal signal had a duration of 400 ms. The on-frequency band was presented alone (reference condition) or with the flanking band. The flanking-band envelope was either correlated or uncorrelated with that of the on-frequency band. Flanking-band center frequencies ranged from 0.25-2.0 kHz. The flanking band was presented either in the same ear as the on-frequency band (monaural condition) or in the opposite ear (dichotic condition). The noise bands had bandwidths of 6.25, 25, or 100 Hz. In the correlated conditions, the flanking-band envelope was delayed with respect to that of the on-frequency band by 0, 5, 10, or 20 ms. For the 100-Hz bandwidth, CMRs were small (typically less than 1 dB) in both monaural and dichotic conditions at all delay times. For the 25-Hz bandwidth, CMRs were about 3.5 dB for the 0-ms delay, and decreased to about 1.5 dB for the 20-ms delay. For the 6.25-Hz bandwidth, CMRs averaged about 5 dB and were almost independent of delay time. The results suggest that the absolute delay time is not the critical variable determining CMR. The magnitude of CMR appears to depend on the correlation between the envelopes of the on-frequency and flanking bands. However, the results do not support a model of CMR that assumes that signal threshold corresponds to a constant change in across-band envelope correlation when the correlation is transformed to Fisher's z.     

The influence of extraneous sounds on the perceptual estimation of first-formant frequency in vowels

The contribution of extraneous sounds to the perceptual estimation of the first-formant (F1) frequency of voiced vowels was investigated using a continuum of vowels perceived as changing from/I/to/epsilon/as F1 was increased. Any phonetic effects of adding extraneous sounds were measured as a change in the position of the phoneme boundary on the continuum. Experiments 1-5 demonstrated that a pair of extraneous tones, mistuned from harmonic values of the fundamental frequency of the vowel, could influence perceived vowel quality when added in the F1 region. Perceived F1 frequency was lowered when the tones were added on the lower skirt of F1, and raised when they were added on the upper skirt. Experiments 6 and 7 demonstrated that adding a narrow-band noise in the F1 region could produce a similar pattern of boundary shifts, despite the differences in temporal properties and timbre between a noise band and a voiced vowel. The data are interpreted using the concept of the harmonic sieve [Duifhuis et al., J. Acoust. Soc. Am. 71, 1568-1580 (1982)]. The results imply a partial failure of the harmonic sieve to exclude extraneous sounds from the perceptual estimation of F1 frequency. Implications for the nature of the hypothetical harmonic sieve are discussed.     

Ueber die antagonistische Wirkung der Neutralsalze auf die Quellung des Fibrins in Säuren und Alkalien

Ohne Zusammenfassung     

Preparation of enediyne-crosslinked networks and their reactivity under thermal and mechanical conditions

The COGEF technique (COnstrained Geometries simulating External Force) was used to investigate the effects of macroscopic forces on cyclic enediynes, which can undergo Bergman Cyclization (BC). Because the forces needed to activate BC were found to be less than the forces needed for chain scission in polymer backbones, the calculations suggest that enediynes are potentially useful mechanophores. Three enediynes studied computationally were synthesized. The thermal BC reactions for these compounds were studied by DSC and found to be consistent with the predicted thermal sensitivity based on known substituent effects. However, upon incorporation of the enediynes into a polymer matrix as crosslinks, no definitive mechanical activation was observed, and conclusions about the stress-sensitivity of enediynes were unable to be drawn. Model studies suggest that insufficient force was applied to the crosslinks for mechanical activation to be observable by DSC.