The superior temporal sulcus has been suggested to play a significant role in the integration of auditory and visual sensory information. Here, we presented vowels and short video clips of the corresponding articulatory gestures to healthy adult humans with two auditory-visual stimulus intervals during sparse sampling 3-T functional magnetic resonance imaging to detect which brain areas are sensitive to synchrony of speech sounds and associated articulatory gestures. The upper bank of the left middle superior temporal sulcus showed stronger activation during naturally asynchronous stimulation than during simultaneous stimulus presentation. It is possible that this reflects sensitivity of the left middle superior temporal sulcus to temporal synchrony of audio-visual speech stimuli.