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The coherence factor (CF) and Wiener postfilter methods have been proposed as effective approaches for reducing the output noise of the delay-and-sum (DAS) beamformer in ultrasound imaging. The theoretical framework between them was also established. However, past researches about the CF and Wiener postfilter methods mainly focused on the summation of an array signal. This paper analyzes the CF and Wiener postfilter in the synthetic aperture (SA) imaging mode, where two-dimensional echo data are recorded. Different CF definitions in the SA imaging are first given and the corresponding Wiener postfilter methods are then proposed, including a Wiener postfilter especially for the SA imaging, named as WienerSA. The performances of different CF and Wiener postfilter methods were evaluated on both simulated and experimental SA data. Results showed that the proposed WienerSA outperformed the other Wiener postfilters in reducing the sidelobe noise level. It obtained the highest contrast ratio among the Wiener postfilter methods, which was even higher than some of the CF methods. Meanwhile it could benefit a much higher contrast-to-noise ratio than those CF methods with further suppression of incoherent noises. Consequently, the WienerSA is believed to be a promising approach in enhancing the SA image quality. [ABSTRACT FROM AUTHOR]

While audiovisual interactions in speech perception have long been considered as automatic, recent data suggest that this is not the case. In a previous study, Nahorna et al. [(2012). J. Acoust. Soc. Am. 132, 1061-1077] showed that the McGurk effect is reduced by a previous incoherent audiovisual context. This was interpreted as showing the existence of an audiovisual binding stage controlling the fusion process. Incoherence would produce unbinding and decrease the weight of the visual input in fusion. The present paper explores the audiovisual binding system to characterize its dynamics. A first experiment assesses the dynamics of unbinding, and shows that it is rapid: An incoherent context less than 0.5 s long (typically one syllable) suffices to produce a maximal reduction in the McGurk effect. A second experiment tests the rebinding process, by presenting a short period of either coherent material or silence after the incoherent unbinding context. Coherence provides rebinding, with a recovery of the McGurk effect, while silence provides no rebinding and hence freezes the unbinding process. These experiments are interpreted in the framework of an audiovisual speech scene analysis process assessing the perceptual organization of an audiovisual speech input before decision takes place at a higher processing stage. [ABSTRACT FROM AUTHOR]