Abstract: Methods and apparatus are described for synchronizing a stimulus with EEG data for research and clinical and consumer applications using EEG and ECG devices. An input/output adapter for stimulus timing includes an adapter input port for receiving an encoded audio file played from an audio output device. The audio file has a first channel carrying trigger data and a second channel carrying stimulus data. The adapter is configured to separate the encoded audio file into its first and second channels; read the trigger data in the first channel and generate a trigger signal for delivery to an EEG data logger; and read the stimulus data in the second channel and generate an auditory signal for delivery to an audio playback device. Timing errors in regard to stimulus onsets are addressed by the synchronized transmission of the trigger signal and auditory signal.