Does a cognitive map guide choices in the radial-arm maze?

Fifteen rats performed in a standard radial-arm maze task (Experiment 1) and in a modified task with a set of forced choices and a 15-min retention interval prior to completion of the maze (Experiment 2). In addition to the standard measure of choice in the radial-arm maze, orientation toward arms was measured and considered to constitute go-no-go "microchoice" decisions. Rats investigated but rejected many arms. A model of choice was developed in which it was assumed that choice decisions about arms were made independently and that microchoices were not selectively guided toward baited arms. The model performed nearly as well as the rats. These results place important limitations on the theory that choice behavior in the radial-arm maze is guided by a cognitive map.     

Components of analogical reasoning in a mildly head injured population

This study sought to investigate the effects of mild head injury on a particular type of cognitive ability, verbal analogical reasoning. The performance of 19 individuals with head injuries was compared to a group of 30 control subjects matched for age, education, and gender on 100 verbal analogies. Solution times and error rates were modeled. Unstandardized regression weights for individual subjects were correlated with subjects’ performance on a number of standardized ability tests. Results showed that compared to the control subjects, the head injured subjects: (a) were significantly slower to solve the analogies, and were particularly slow to perform certain processes: encoding/inference and comparison; (b) tended to show greater variability in performance; and (c) had data that had a poorer componential model fit. The data suggest that analogical reasoning is affected by a head injury, and that certain information processes may be responsible for performance deficits.     

The epidemiology of suicide and attempted suicide

Since more than one century suicides have been registered in national statistics of death causes. They thus furnish one of the few parameters of psychiatrically relevant behaviour by means of which trends, cohort, age-group and period effects can be studied over longer periods. Since the second half of last century, the suicide rates for Swiss males--similar to those found in England and Wales--show a decrease in consecutive birth cohorts up to males born in the decade 1930-1940, and a continued decline in the total trend until about World War II. From then on the suicide rates of males in consecutive birth cohorts have been slowly increasing in the majority of European and North American countries--but not so in Sweden. Opposite to this, the predominantly low rates for females display little change. Further to the considerable differences between nations and the predominance of suicides committed by females in some Asian countries and Cuba, the changes indicate the significance of cultural and economic environmental factors. Typical period effects are mainly the result of changes in conception and conditions of life. In attempted suicide they proceed in a more sensitive and more rapid way and are about ten times higher. Such a period effect showing increases by about 300% in younger age-groups followed by a decline, attaining its peak about 1976, was ascertained in large cities of the Federal Republic of Germany. By the example of the effects of a television serial, the study of causal processes turning collective environmental factors into individual suicidal behaviour, proved that regularities are effective in learning by a process of modelling. Besides, the epidemiological data give essential hints how to treat suicidal behaviour.     

HIV infection: trauma and coping with trauma

The initial results of a German-Swedish research project demonstrate the at times active-resistant and at times passive-resigned approaches of AIDS patients toward their illness.     

Threshold tracking for assessment of long-term adaptation and sensitization in pain perception

To assess temporal variations in the perception of "phasic" heat pain stimuli a psychophysical tracking procedure was developed that enables repeated assessment of the pain threshold at short intervals. This "double-tracking" procedure produces two tracking curves simultaneously, one that approaches the pain threshold gradually from above, the other from below. The threshold for phasic heat pain was measured in 80 tracking trials with stimuli at temperatures near the pain threshold. Concurrently, the threshold for "tonic" heat pain was determined after every 20 tracking trials with a stimulus adjustment procedure. Eleven healthy subjects (age: 26.4 yr. +/- 6.0) participated in 2 sessions each. Phasic stimulation near the pain threshold did not produce any trends in either of the two threshold measures. Hence there was no long-term adaptation or sensitization. However, there were random variations (random walks) in the tracking curves, which we interpret as resulting from a stochastic relationship between stimulus and sensation. In agreement with other reports, discrimination seemed to be better at painful than at nonpainful temperatures.     

Decision time and movement time in depression: differential effects of practice before and after clinical improvement

Choice reaction time involves, at least two components of response latency, decision time and movement time. Studies of choice reaction time usually provide values of these two components averaged over a given number of trials. The aim of the present study of depressed subjects was to investigate changes across practice on Decision Time (DT) and Movement Time (MT) before and after clinical improvement. 19 depressed subjects were given two sessions of 50 trials each, one before treatment (Di) and one after recovery (Df). Decision time and movement time exhibited quite different patterns. Decision time significantly decreased with clinical improvement. No significant variation across trials was found, in either session. Movement time values varied across trials but the variations observed on Di and Df were significantly different, whereas before treatment latencies recorded at the end of the session were greater than those scored at the start, the contrary was observed after clinical recovery. No significant difference was found between values of movement time scored at the start of the two sessions.     

On the logic of causally necessary and sufficient conditions: Towards a theory of motive-explanations of human actions

Research carried out under the auspices of the Bank of Sweden. Tercentenary Foundation project RJ 86/183: Basic Concepts of Procedural Law in the Light of Present-Day Philosophy of Language and Linguistics.