Four-button digital response box for ActiveTwo. Small, hand-held response box with four buttons providing zero-lag digital output directly to Biosemi ActiveTwo's built-in trigger input port and logged in the EEG data file as triggers. Cable would be constructed to permit the experimenter also to press Function keys 1-8 to introduce distinct triggers into the EEG data file. No additional software (e.g. stimulus delivery software) is required to use this button box.