The assessment of individual differences between young children with a pervasive developmental disorder by means of behaviour scales which are derived from direct observation.

Data obtained by direct observation of 112 3-6-year-old normal children and 31 children with a pervasive developmental disorder aged 3-6 were used to construct behaviour scales by means of simultaneous component analysis. This is a technique for finding behaviour clusters (components) common to different groups by weighting the variables such that the resulting components maximize variance accounted for when summed over the groups (Milsap & Meredith, 1988, Psychometrika, 53, 123-134; Berge & Kiers, 1990, Nederlands Tijdschrift voor de Psychologie, 45, 221-226). An evaluation of the component structure that was found is given for both groups. Results show uncorrelated components for the normal group, while some of the same components are intercorrelated in the clinical group. Scales were constructed which are shown to have discriminative value with respect to subgroups within the group of patients.

Appropriate conditions for maintenance of chimpanzees in studies with blood-borne viruses: an epidemiologic and psychosocial perspective.

Based on the know epidemiology of the viruses that account for the bulk of the need for chimpanzees in biomedical research--hepatitis B virus (HBV), non-A, non-B (NANB) hepatitis virus, and human immunodeficiency virus (HIV)--as well as the psychosocial needs of this species, requirements for appropriate isolation conditions for these animals have been reviewed. We believe that animals should generally be housed in groups of at least two in the same cage, and that cages encased in solid-walled isolator boxes for housing of single chimpanzees are unnecessary for virologically adequate isolation for studies of HBV, NANB and HIV, and cause sensory and psychosocial deprivation, which contravenes their psychological well-being.

Detection of low dose effects of psychopharmaca: Application of a semi-Marcov model to rhesus monkey behaviour.

Behavioural testing of psycho-active drugs at lower doses is needed for medical applications and for the study of pharmacological brain mechanisms. Sensitive methods to detect effects on the time structure of behaviour are lacking. We propose a procedure based on a description within the framework of continuous time Marcov chain models. This class of models is generalized to account for constraints on the organisation of a motor pattern including the speed at which it is terminated. This leads to semi-Marcov models with transition rates that quickly increase from zero to a constant level. We describe and compare several models. As an application we consider amphetamine effects on infant rhesus monkeys. One of the models is preferred since, besides giving a good fit, it demonstrates consistent amphetamine effects that can be interpreted as short-term effects on motor constraints. Amphitamine also induced more mother-directed behaviour. We give maximum likelihood procedures for behaviour analysis based on the preferred model.

Regulation of nursing in chimpanzees.

The regulation of nursing was studied in captive chimpanzees from birth to 6 months of age. It was asked whether regulation was predictable or timing was irregular. A search for unimodal frequency distributions resulted in a distinction among nursing bouts, nursing episodes (bouts with brief interruptions) and nursing pauses. The frequency distributions of these types were either normal with very large standard deviations or exponential (i.e., randomly terminated). This implies a very irregular timing. Longer nursing episodes were followed by somewhat longer pauses; pauses with daytime sleep (that were relatively long) were followed by longer nursing. However, these regulatory effects were only slight. Most of this loose regulation of nursing was due to the infant, as the mothers did not put the infant on the breast and usually were permissive. Comparisons with humans suggest a similarly loose organization as well as frequent feeding in societies that provide relatively unlimited access to the breast. The regular 4-hr, meal-like schedule in industrial countries seems mainly to be due to human mothers and their advisors.

Quantitative criteria for attention and activity in child psychiatric patients.

The aim was to find empirically justified criteria for attention and activity. Patients with various disorders and controls were observed during psychiatric examinations. Measures of attention increased with age, were lower in patients than controls, were correlated with each other and related to the quality of task performance. Activity measures decreased with age, were higher in patients, were correlated among each other and concerned motility as well as talking initiatives. Criteria from other studies and the DSM-III were critically examined. Inattention was not associated with hyperactivity, except in mentally retarded children. Inattention was common in many diagnostic categories.

Recommendations for the housing of macaque monkeys.

A multidisciplinary working group was formed to make recommendations for housing of macaques under laboratory conditions in the Netherlands. The group concluded that long-term individual caging leads to persistent abnormal behaviour. Therefore, individual housing is regarded as acceptable only for special reasons which counter-balance the adverse effects of isolation. Guidelines are given for developing more satisfactory social housing systems. Cages used in individual as well as social housing should meet certain spatial and other requirements to ensure a certain amount of diversion, freedom of movement and safety. Since the recommendations represent the opinion of experts in certain aspects of animal husbandry, the report can be used as a legal reference under the Animal Experiments Act.

Social play and rank order in rhesus monkeys (Macaca mulatta.

Social play is indispensable for adequate social development. Several authors have described a correlation between a mother's rank in the hierarchy and the rank of her infant. How the mother's rank is passed on to her infant was investigated. Social play in particular was studied. Social play among group members of rhesus monkeys (Macaca mulatta) was quantified in the laboratory. The group initially consisted of one adult male, six adult females and two infants. Four additional infants were born during the study period, all females. For each mother, social rank and order of giving birth was identical. There was a positive correlation between the social rank of the mother and the frequency of play. For the younger infants, this was not significantly due to age. Most play occured with the infant of the next (higher or lower) rank. The results suggest that both the amount of play and the partner's rank predispose the young monkey to assume its mother's rank.