Despite over half a century of intensive research the essential nature of the schizophrenias still remains an enigma. Attempts to account for the disordered behaviour of the schizophrenic have ranged over the full spectrum of the biosocial sciences, explanations being sought both in the biochemistry of the organism and in the interpersonal relationships of the whole individual. Sitting somewhere between these two extremes is the psychophysiological view. As a conceptual and methodological approach to behaviour in general, psychophysiology concerns itself with the problem of integrating neurophysiological and psychological data, attempting to bridge the gap between these two disciplines. Of course, the potential value of describing behaviour at a different level of explanation, either more molecular or more molar, is not denied. However, the peculiar contribution of psychophysiology is its concentration on data gathered at the interface between the brain and behaviour. As such its techniques are chosen so as to allow guesses to be made about the functional systems in the brain that underly behaviour. They naturally include the study of E.E.G. and autonomic response but also extend to the measurement of various phenomena derived from conventional experimental psychology, such as perceptual thresholds and vigilance (Claridge, 1970b). The theoretical concepts of psychophysiology reflect its mongrel background and include such terms as ‘arousal’, a notion originating in academic psychology, but made respectable by neurophysiologists.