Figure 1.

An example session of experimental paradigm. Subjects were presented alternating blocks of four different visual stimuli: checkerboard, words, sign language, and lip-reading. The order of presentation was pseudorandomly assigned. For each subject, there were 20 blocks (four stimuli × five repetitions), with each stimulus presented for 20 s and the black screen sustained for 20 s as an interval. The whole experiment was separated into three sessions for the purpose of avoiding subject fatigue. Throughout a block, subjects were asked to either fixate on a red cross at the center of the screen or concentrate on the visual stimuli. Questions were asked at the end of the experiment to ensure that subjects had paid attention to the visual stimuli (Supporting information).