• Motion sickness susceptibility can be used as a neurophysiologic index to establish a polar spectrum of personality difference. Previous observations on a psychiatric patient population have shown that persons in transition between these extremes enter the hospital at a younger age, have a longer stay, and are more likely to receive a diagnosis of schizophrenia. The relationship of this midspectrum, early-onset disorder to other psychotic illnesses has been unclear. Examination of a large sample shows that a midspectrum psychiatric illness, which is most common in young men and is usually diagnosed as schizophrenia, is balanced at the extremes of susceptibility by an olderonset illness, which is most common in women and is often diagnosed as affective in nature. A gradual transition appears to exist between the two types of illness.