Journal Article

The Natural Statistics of Audiovisual Speech

Ghazanfar, Asif A., Chandrasekaran, Chandramouli, Trubanova, Andrea, Caplier, Alice, Stillittano, Sébastien

2009

Overview

Humans, like other animals, are exposed to a continuous stream of signals, which are dynamic, multimodal, extended, and time varying in nature. This complex input space must be transduced and sampled by our sensory systems and transmitted to the brain where it can guide the selection of appropriate actions. To simplify this process, it's been suggested that the brain exploits statistical regularities in the stimulus space. Tests of this idea have largely been confined to unimodal signals and natural scenes. One important class of multisensory signals for which a quantitative input space characterization is unavailable is human speech. We do not understand what signals our brain has to actively piece together from an audiovisual speech stream to arrive at a percept versus what is already embedded in the signal structure of the stream itself. In essence, we do not have a clear understanding of the natural statistics of audiovisual speech. In the present study, we identified the following major statistical features of audiovisual speech. First, we observed robust correlations and close temporal correspondence between the area of the mouth opening and the acoustic envelope. Second, we found the strongest correlation between the area of the mouth opening and vocal tract resonances. Third, we observed that both area of the mouth opening and the voice envelope are temporally modulated in the 2-7 Hz frequency range. Finally, we show that the timing of mouth movements relative to the onset of the voice is consistently between 100 and 300 ms. We interpret these data in the context of recent neural theories of speech which suggest that speech communication is a reciprocally coupled, multisensory event, whereby the outputs of the signaler are matched to the neural processes of the receiver.

• Publisher: Public Library of Science,PLOS,Public Library of Science (PLoS)
• Subject: Brain / Colleges & universities / Computer Science / Computer Science/Natural and Synthetic Vision / Databases, Factual / Engineering Sciences / Fourier Analysis / Humans / Image Processing, Computer-Assisted - methods / Models, Statistical / Mouth / Mouth - physiology / Neuroscience/Cognitive Neuroscience / Neuroscience/Motor Systems / Neuroscience/Natural and Synthetic Vision / Neuroscience/Sensory Systems / Neuroscience/Theoretical Neuroscience / Neurosciences / Physiological aspects / Psychological aspects / Sensory stimulation / Signal and Image processing / Signal Processing, Computer-Assisted / Speech / Speech - physiology / Speech Perception - physiology / Statistics / Time Factors / Visual Perception - physiology / Voice - physiology