Poisson signal-detection theory: Link between threshold models and the Gaussian assumption

The Gaussian model of signal detection cannot fit asymmetric data as long as the variances of the distributions are kept equal. It is therefore common practice to assume unequal variances in order to fit these data. But this assumption leads to the well-known crossover problem. The present paper provides new arguments for the abandonment of the Gaussian model with unequal variances. In its stead, this paper reevaluates multiple-parallel-threshold models. In particular, the Poisson model turns out to be very useful: it can handle data with any degree of asymmetry, giving a reasonable interpretation of the two parameters of the receiver-operating characteristic. The three-state-threshold model (Krantz, 1969) is given a new interpretation in light of the Poisson model. The slope of Poisson double-probability plots turns out to be much closer to unity than is predicted by the Gaussian approximation.     

Prophylactic psychiatry

The great contributions of Gantt to the problems of prophylactic psychiatry are pointed out. The author reviews his experiences with a 30-year follow-up of a population of 1800 persons. Over the 30 years, there appeared to be a 50% increase of neuroses, which raises great problems for mental health services. The Berlevåg population was offered optimal psychiatric services. Behavior therapy of neuroses and drug treatment of depression may possibly have lowered the prevalence of mental disorders. Psychophysiologic tests were used in the project. It is hoped that such tests may be utilized for early detection and treatment of mental disorders.     

Differential effects of person in the dog and in the human

People have marked effects on dog’s heart rate, with great individual variations for different persons. Apparently people to which the dog is attached have the greatest effect upon heart rate. Replications of the animal experiments using the psychotherapist and two other people revealed no effects upon the heart rate of a schizophrenic human. In the human the effects of people are probably best demonstrated in connection with verbal communication.