Abstract: The aim of the present study was to investigate the human brain’s audiovisual integration mechanisms for letters, i.e., for stimuli that have been previously associated through learning. The subjects received audiovisual (AV) letters of the Chinese characters and were required to identify them, regardless of stimulus modality. The brain activations were detected with electroencephalogram (EEG), which is well suited for noninvasive identification of cortical activity and its accurate temporal dynamics. The present study was able to find evidence of both non-phonetic and phonetic audiovisual interactions in the Event-Related Potentials (ERPs) to the same AV stimuli. In addition, the differences in the ERPs to the meaningful and meaningless of AV stimuli probably reflect multisensory interactions in phonetic processing. When acoustic and visual phonemes were meaningful, they formed a natural multisensory interaction stimulus. The present study demonstrates that the audiovisual interaction is an indicator for investigating the automatic processing of suprasegmental information in tonal language. Multisensory integration of letters (orthography) and speech sounds of tonal language in the human auditory association cortex showed a strong dependency on the relative timing of the inputs. The critical role of input timing on multisensory integration has been demonstrated before at the neuronal level for naturally related visual and auditory signals.