Poster B66, Sunday, March 26, 8:00 – 10:00 am, Pacific Concourse
Visual cortex entrains to low-frequency amplitude variability in sign language
Geoffrey Brookshire1, Jenny Lu1, Howard Nusbaum1, Susan Goldin-Meadow1, Daniel Casasanto1; 1The University of Chicago
Despite immense variability across languages, children can learn any human language, including sign languages. What neural mechanisms allow people to learn and understand language across sensory modalities? When people listen to speech, electrophysiological oscillations in auditory cortex entrain to slow (<8 Hz) fluctuations in the acoustic envelope. Entrainment to the speech envelope may reflect mechanisms specialized for auditory perception. Alternatively, entrainment may be a general-purpose cortical mechanism that optimizes sensitivity to rhythmic information regardless of modality. We test these proposals by examining cortical entrainment to rhythmic fluctuations in the visual amplitude of sign language. First, we develop a metric to characterize visual amplitude at each time-point. We demonstrate quasi-periodic fluctuations in the amplitude of sign language, and show that oscillations tend toward lower frequencies in sign than in spoken language. Next, we test for entrainment of neural oscillations to visual oscillations in sign language, using electroencephalography (EEG) in fluent speakers of American Sign Language (ASL) as they watch videos of ASL. We find significant cortical entrainment to visual oscillations in sign language. Coherence to sign language emerges only below 5 Hz, and peaks at about 1 Hz. Although coherence to speech is strongest over auditory cortex, we find the strongest coherence to sign at occipital and parietal sites. These results demonstrate that cortical coherence to linguistic stimuli does not depend on neural processes specific to auditory perception of speech. Low-frequency oscillatory entrainment may reflect a general cortical mechanism that maximizes sensitivity to informational peaks in time-varying signals.
Topic Area: LANGUAGE: Other