Is stimulus persistence affected by eye movements?

Summary When an eye movement intervenes between the presentation of a target and a mask, the mask has its effect on material projected on the same retinal position. Davidson, Fox, and Dick (1973) reported, however, that the mask appears to be positioned in real space, a suggestion which implies integration of visible information across the eye movement. The present note argues that their conclusion does not follow from their data.     

Intracerebroventricular injection of anti-prolactin serum suppresses excessive grooming of pituitary homografted rats

Rats with endogenous hyperprolactinaemia, as induced by pituitary homografts under the kidney capsule, displayed increased grooming behavior as compared to that of sham-operated animals. Twelve days after surgery, intracerebroventricular injection of anti-prolactin serum (dilution 1:100, 1 microliter) suppressed the excessive grooming of homografted rats. These observations suggest that prolactin from a peripheral source may reach the central nervous system to affect brain mechanisms involved in grooming behavior.     

The influence of neurotensin, naloxone, and haloperidol on elements of excessive grooming behavior induced by ACTH

Naloxone, haloperidol, and neurotensin suppress ACTH-induced grooming. The suppressive effects of naloxone and of haloperidol on ACTH-induced grooming are observed following subcutaneous as well as intracerebroventricular administration. The suppression of ACTH-induced grooming by these drugs is not accompanied by a change in the relative distribution of grooming elements. From previous data and from the results of the present study it is suggested that the underlying substrate involved in ACTH-induced excessive grooming may differ from that of bombesin-induced grooming.     

The societal and psycho-sociological background of football hooliganism

On October 11, 1985, the Belgian Council of Ministers ordered scientific research on violence on the football terraces. This research was conducted in the years 1986 and 1987 by the “Onderzoeksgroep Jeugdcriminologie” (Research group on Juvenile Criminology) of the K.U. Leuven in close relationship with the general police of the home office. (The report was submitted on December 23, 1987 [VAN LIMBERGEN, COLAERS en WALGRAVE, 1987].)     

Adolescent smoking intentions: gender differences in peer context.

Despite widespread interest in adolescent smoking behavior, little research has been directed to the social dynamics of adolescent smoking. In this paper, smoking intentions and peer group influences among a sample of 1,689 Grade 8 students from southern Ontario were analyzed to ascertain possible gender-specific correlates in adolescent smoking intentions. The peer environment was found to be a crucial factor in adolescent smoking behavior. Particularly striking for adolescent girls was the firmness of their expressed intentions to continue to smoke quite early in their smoking lives.     

Learning the cascade juggle: a dynamical systems analysis

How beginning jugglers discover the temporal constraints governing the juggling workspace while learning to juggle three balls in a cascade pattern was the subject of this investigation. On the basis of previous theoretical and experimental work on expert jugglers, we proposed a three-stage model of the learning process, for which objective evidence was sought. The first stage consists of learning to accommodate the real-time requirements of juggling, as expressed in Shannon's equation of juggling, which states that, averaged over time, the cycle time of the hands should be a fixed proportion of the cycle time of the balls. The second stage of learning consists of discovering the primary frequency lock of.75 between the shorter term dynamical regime underlying the repetitive subtask of transporting a ball and the longer term dynamical regime underlying the total hand loop cycle. The third and last stage of learning consists of discovering the principles of frequency modulation from.75 to lower (averaged) values of the proportion of time that a hand carries a ball during the total hand cycle time. Twenty subjects were taught to juggle three balls in a cascade pattern. Ten subjects were trained with the aid of an instructor and a metronome, and 10 with the instructor only. The metronome proved to be of no particular additional help, but the timing results obtained were in agreement with the proposed three stages of learning. The picture that emerged from this study was that learning a new motor skill involves the discovery of invariance's or fixed points in the perceptual-motor workspace associated with that skill, from which excursions can be made and the skill further refined. Because these fixed points afford stability of operation, discovering them logically and factually precedes the acquisition of the functional adaptability and flexibility of operation ("flair") inherent to frequency modulation.     

The EM algorithm for latent class analysis with equality constraints

The EM algorithm is a popular iterative method for estimating parameters in the latent class model where at each step the unknown parameters can be estimated simply as weighted sums of some latent proportions. The algorithm may also be used when some parameters are constrained to equal given constants or each other. It is shown that in the general case with equality constraints, the EM algorithm is not simple to apply because a nonlinear equation has to be solved. This problem arises, mainly, when equality constrints are defined over probabilities indifferent combinations of variables and latent classes. A simple condition is given in which, although probabilities in different variable-latent class combinations are constrained to be equal, the EM algorithm is still simple to apply.The authors are grateful to the Editor and the anonymous reviewers for their helpful comments on an earlier draft of this paper. C. C. Clogg and R. Luijkx are also acknowledged for verifying our results with their computer programs MLLSA and LCAG, respectively.