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.     

Extensions of Rasch's multiplicative poisson model

Consideration will be given to a model developed by Rasch that assumes scores observed on some types of attainment tests can be regarded as realizations of a Poisson process. The parameter of the Poisson distribution is assumed to be a product of two other parameters, one pertaining to the ability of the subject and a second pertaining to the difficulty of the test. Rasch's model is expanded by assuming a prior distribution, with fixed but unknown parameters, for the subject parameters. The test parameters are considered fixed. Secondly, it will be shown how additional between- and within-subjects factors can be incorporated. Methods for testing the fit and estimating the parameters of the model will be discussed, and illustrated by empirical examples.     

Single-letter recognition accuracy and position information: Benefits with a symbolic cue

Summary This study reports two experiments designed to test a model that has as a basic assumption that position information is at the basis of the cueing benefits observed in single-item recognition tasks with accuracy as the dependent variable. In the experiments, two cueing conditions were used; a 100%-valid symbolic-cue condition and a neutral-cue condition. In Experiment 1, in which position information was sometimes missing, the symbolic cue brought a significant benefit. In Experiment 2, in which position information was always available, no benefit was obtained. These results are consistent with, and support, the model. Improved knowledge of position is at the basis of the cueing benefits observed in this type of task.     

Daily-life difficulties in person recognition reported by young and elderly subjects

Elderly people frequently complain spontaneously about their inability to remember people and their names. Naturalistic methods such as diaries, checklists, etc. provide useful means to study and make more explicit the nature of such memory difficulties among the elderly, as well as to better understand normal memory functioning. We developed a checklist (inspired by a study by Young, Hay and Ellis, 1985) to explore normal young and elderly people's difficulties in person recognition. The checklist is composed of four parts, each one corresponding to a particular context in which the difficulty took place. Each part has the same structure and consists of precise questions about the type of incident, the circumstances, the persons involved, and the way the incident ended. Three groups of normal subjects kept records of their difficulties and errors in recognizing people for 1 month: young subjects with a bad memory for faces, young subjects without particular problems of face memory, and a group of elderly subjects. A total of 299 records were collected. They were classified with respect to the functional components presumably implied in the process breakdown. The elderly subjects experienced difficulties with retrieving names, first names, or nicknames (Name Codes), while the young subjects with a bad memory for faces reported overall the greatest number of incidents and were particularly impaired in access to Face Recognition Units. A characterization of these two kinds of difficulties is proposed. Young subjects without problems of face memory presented equal numbers of difficulties at all stages of person recognition. These patterns of results will be discussed in terms of current cognitive models of person recognition.     

Self- and interview-rated negative mood states in schizophrenia: Their convergence and prediction of thought disturbance

This longitudinal study evaluated the relations between self- and interview-rated negative mood in schizophrenics and compared the prognostic utility of these two methods. Thirty schizophrenics who had been stabilized on neuroleptic medications were evaluated with self-report and interview-based measures of mood and symptomatology at an initial assessment and again at 6-month follow-up. Results indicated that measures of self- and interview-rated negative mood showed little agreement at the initial assessment; however, at follow-up, significant convergent correlations between the two methods were obtained. Self-reported negative mood at the initial evaluation predicted the severity of thought disturbance at follow-up, whereas interview-based ratings of mood did not. The results underscore the importance of conducting multimethod assessments of mood and support other research suggesting that self-reported negative mood states may predict course of the illness in schizophrenia.This research was supported by National Institute of Mental Health (NIMH) Grants MH38636 and MH39998 and by a grant from the National Alliance for Research in Schizophrenia and Depression (NARSAD). Jack J. Blanchard was also supported in part by NIMH Grant MH18932 for the Collaborative Training Program in Schizophrenia Research at the Medical College of Pennsylvania/EPPI. Portions of this research were presented at the 24th Annual Meeting of the Association for the Advancement of Behavior Therapy, San Francisco, California, November 2, 1990, and at the 3rd International Congress on Schizophrenia Research, Tucson, Arizona, April 22, 1991.