Temporal synchrony is required for across-modality interactions. A, B, The number of reported flashes (A) or beeps (B) for V₁v₁ A₂a₂ stimuli when the acoustic stimuli was delayed by 30 ms, relative to the visual stimuli, or by 300 ms. The across subject mean ± SEM (black diamonds) are overlaid on the individual subject data (gray lines).