We report a technique for studying interactions among many subsystems of a biological system. A general mathematical technique is developed for information flow among various subsystems of a system when two or more classes of stimuli are presented to the system. The technique is validated by various simulation studies and then applied to a brain system. The usefulness of the technique is demonstrated for visual event related potentials (ERP's) obtained from human subjects suffering from phobias. The stimuli are briefly flashed words and phrases. The word classes are pleasant, unpleasant, conscious, and unconscious. The conscious class consists of words known by the patient to relate to the problem, whereas the unconscious class of words consists of words related to deep conflicts which are not recognized by the patient. It is demonstrated that information flow is suppressed under supraliminal presentation of the unconscious class, but is strong under subliminal presentation. The technique has the potential of being an objective indicator of conflictual relationships in these patients. The principle of the technique can be applied to any system in which interactions among subsystems are to be analyzed.