It is a well-known principle in psychology that the effects of sensory stimulation do not cease when the stimulus itself ceases. The so-called visual after-images are probably the best known of these after-effects, but almost equally well known are those induced by a rotating spiral. If a normal person fixates the centre of the rotating spiral for a period of time, and if then the motion of this spiral is suddenly stopped, an after-sensation of movement is well nigh universal. This after-sensation is opposite to the original motion in direction, just as the after-image produced by the fixation of a colour is usually the complementary colour to that which caused the original perception. There is little doubt that while peripheral factors play some part in these after-effects, central features also play a part, and it becomes tempting, therefore, to use phenomena of this type in attempts to verify or disprove the drug action hypotheses advanced by one of us in a previous paper. This hypothesis stated that stimulant drugs increased excitatory potential and decreased inhibitory potential, while depressant drugs decreased excitatory potential and increased inhibitory potential. The question now arises as to how this general postulate can be applied to the phenomena under discussion.

In the first paper of this series, it was pointed out that one of the reasons why McDougall's theory of drug action and personality was not accepted at all widely was connected with the fact that he failed to provide an objective, experimental test which could be used to diagnose extraversion-introversion, and to assess drug effects. This argument is not entirely correct; McDougall did in fact suggest one such test, namely the rate of fluctuation of so-called reversible perspective figures. Many varieties of these are known, and have been used experimentally; the Necker cube, the staircase, the vase-face, and the windmill patterns being probably the best known. In all of these, there is an ambiguity in the drawing which makes it possible to perceive two distinct patterns in the stimulus; on prolonged inspection these patterns alternate, and it is the rate of alternation, signalled verbally or by suitable mechanical arrangement, which constitutes the score on this test. It is known that different types of pattern give reasonably reliable scores, and also that rates of alternation on different patterns correlate quite highly together, thus demonstrating that one and the same tendency is being measured. That this tendency is of central rather than peripheral character is indicated by the fact that changes in the rate of reversal due to fatigue and other causes can be transferred from one eye to the other.

In a previous paper in this series, a brief discussion has been given of the theoretical reasons for anticipating that depressant drugs would shorten the perceptual after-effects of visual stimuli, and stimulant drugs would lengthen these effects. The present paper is concerned with a related type of prediction, also concerned with certain visual after-effects. The phenomenon in question was first observed by Bidwell; it has not received much study, unfortunately, in spite of its great theoretical interest. The phenomenon is simply this. If a beam of red light (the primary stimulus, or Sp) is thrown into the eye of a person having normal colour vision, that person will report a red sensation, followed after the extinction of the light source by a series of after-images, usually in the complementary colour. The theory governing the appearance of the after-image is conventionally a photochemical one; the Sp produces certain effects in the retina which are opposite in direction for complementary colours and which are reversed when the Sp ceases to act on the retina. This reversal is perceived as the complementary after-image. Bidwell discovered that when the Sp is shown only for a relatively short period of time, say 20 milliseconds, and is immediately followed by a neutral stimulus, such as a beam of white light, then the S is not perceived at all, but only the complementary after-image. In other words, a red stimulus is perceived as green, a green stimulus as red. It is this perception of a non-existent stimulus which caused the phenomenon to be of such interest to psychologists.

This paper sets out to demonstrate similarities of behaviour between obsessionals and hysterics in responses to perceptual conflict, which might be expected on the basis of psycho-analytical theories, but which could not be predicted from the dimensional framework of personality favoured by Eysenck in which obsessionals and hysterics are found at opposite poles of an introversion-extroversion continuum, and in which anxiety states, depressives and obsessionals are grouped together in one indistinguishable category of dysthymia.

Chemically hydroxyzine is one of a series of p-chlorobenzhydryl piperazine derivatives. It has a formula as follows: