Constrained maximum likelihood estimation of two-level covariance structure model via EM type algorithms

In this paper, the constrained maximum likelihood estimation of a two-level covariance structure model with unbalanced designs is considered. The two-level model is reformulated as a single-level model by treating the group level latent random vectors as hypothetical missing-data. Then, the popular EM algorithm is extended to obtain the constrained maximum likelihood estimates. For general nonlinear constraints, the multiplier method is used at theM-step to find the constrained minimum of the conditional expectation. An accelerated EM gradient procedure is derived to handle linear constraints. The empirical performance of the proposed EM type algorithms is illustrated by some artifical and real examples.This research was supported by a Hong Kong UCG Earmarked Grant, CUHK 4026/97H. We are greatly indebted to D.E. Morisky and J.A. Stein for the use of their AIDS data in our example. We also thank the Editor, two anonymous reviewers, W.Y. Poon and H.T. Zhu for constructive suggestions and comments in improving the paper. The assistance of Michael K.H. Leung and Esther L.S. Tam is gratefully acknowledged.     

Closing the gap between behavior and models in route choice: The role of spatiotemporal constraints and latent traits in choice set formation

A considerable gap exists between the behavioral paradigm of choice set formation in route choice and its representation in route choice modeling. While travelers form their viable choice set by retaining routes that satisfy spatiotemporal constraints, existing route generation techniques do not account for individual-related spatiotemporal constraints. This paper reduces the gap by proposing a route choice model incorporating spatiotemporal constraints and latent traits. The proposed approach combines stochastic route generation with a latent variable semi-compensatory model representing constraint-based choice set formation followed by compensatory choice. The model is applied to data focusing on habitual commuting route choice behavior in morning peak hours. Results show (i) the possibility of inferring spatiotemporal constraints from considered routes, (ii) the importance of incorporating spatiotemporal constraints and latent traits in route choice models, and (iii) the linkage between spatiotemporal constraints and time saving, spatial and mnemonic abilities.     

Women’s everyday mobility: Frightening situations and their impacts on travel behaviour

This paper investigates frightening situations women face in their everyday mobility. The focus is not on serious criminal offences but rather on all situations causing fear such as harassment and the influence on the travel behaviour of women. Two surveys were conducted in Austria in 2012 and 2013 to assess whether and how many women are affected and to get insights in locations of the incidents and the circumstances. The personal security aspects of different modes of transport are investigated. The results show that women who experienced frightening situations tend to avoid certain destinations or routes and travel modes more than other women. The results also confirm that women in general have constrained travel behaviour because of fear about their personal security. When it is impossible to change route or travel time e.g. due to personal restraints, or when simply no other transport mode is available, women are captives to use unwanted transport options, even when they have to reckon with frightening situations. The conclusions summarize that women’s personal security plays an important role in terms of travel behaviour and increased attention should be paid by authorities as well as city- and transport planners striving for sustainable built environments. As the share of affected women is high and it can be assumed that women are more often imperilled than men the questions arises, if this can be assimilated to unequal mobility opportunities, finally resulting in a social deficiency for women.     

Reward magnitude effects on temporal discrimination

Changes in reward magnitude or value have been reported to produce effects on timing behavior, which have been attributed to changes in the speed of an internal pacemaker in some instances and to attentional factors in other cases. The present experiments therefore aimed to clarify the effects of reward magnitude on timing processes. In Experiment 1, rats were trained to discriminate a short (2 s) vs. a long (8 s) signal followed by testing with intermediate durations. Then, the reward on short or long trials was increased from 1 to 4 pellets in separate groups. Experiment 2 measured the effect of different reward magnitudes associated with the short vs. long signals throughout training. Finally, Experiment 3 controlled for satiety effects during the reward magnitude manipulation phase. A general flattening of the psychophysical function was evident in all three experiments, suggesting that unequal reward magnitudes may disrupt attention to duration.     

Specificity of Task Constraints and Effects of Visual Demonstrations and Verbal Instructions in Directing Learners' Search During Skill Acquisition

In the present study, the efficacy of visual demonstrations and verbal instructions as instructional constraints on the acquisition of movement coordination was investigated. Fifteen participants performed an aiming task on 100 acquisition and 20 retention trials, under 1 of 3 conditions: a modeling group (MG), a verbally directed group (VDG), and a control group (CG). The MG observed a model intermittently throughout acquisition, whereas the VDG was verbally instructed to use the model's movement pattern. Participants in the CG received neither form of instruction. Kinematic analysis revealed that compared with verbal instructions or no instructions, visual demonstrations significantly improved participants' approximation of the model's coordination pattern. No differences were found in movement outcomes. Coordination data supported the visual perception perspective on observational learning, whereas outcome data suggested that the modeling effect is mainly a function of task constraints, that is, the novelty of a movement pattern.     

Do Children Perceive Postural Constraints When Estimating Reach or Action Planning?

Estimation of whether an object is reachable from a specific body position constitutes an important aspect in effective motor planning. Researchers who estimate reachability by way of motor imagery with adults consistently report the tendency to overestimate, with some evidence of a postural effect (postural stability hypothesis). This idea suggests that perceived reaching limits depend on an individual's perceived postural constraints. Based on previous work with adults, the authors expected a significant postural effect with the Reach 2 condition, as evidenced by reduced overestimation. Furthermore, the authors hypothesized that the postural effect would be greater in younger children. They then tested these propositions among children aged 7, 9, and 11 years by asking them to estimate reach while seated (Reach 1) and in the more demanding posture of standing on 1 foot and leaning forward (Reach 2). Results indicated no age or condition difference, therefore providing no support for a postural effect. When the authors compared these data to a published report of adults, a developmental difference emerged. That is, adults recognize the perceived postural constraint of the standing position resulting in under- rather than overestimation, as displayed in the seated condition. Although preliminary, these observations suggest that estimates of reach (action planning) continue to be refined between late childhood and young adulthood.     

Interlimb Coordination: Real Constraints and False Dichotomies

Despite the recent advances in the field of coordination dynamics addressing the interplay of constraints of different natures in the emergence of human coordination, F. Mechsner (2004) invites us to revive hierarchical and dichotomous thinking by offering again his exclusive position that coordinated movements are (purely) perceptual-cognitive/psychological in nature. In this comment, the authors address a number of theoretical and methodological issues that might potentially puzzle the readers of Mechsner's article. They contend that the dichotomy proposed by Mechsner (i.e., perceptual-cognitive vs. motor) constitutes a restrictive framework for understanding human coordination.     

Interpersonal Pattern Dynamics and Adaptive Behavior in Multiagent Neurobiological Systems: Conceptual Model and Data

ABSTRACT

Ecological dynamics characterizes adaptive behavior as an emergent, self-organizing property of interpersonal interactions in complex social systems. The authors conceptualize and investigate constraints on dynamics of decisions and actions in the multiagent system of team sports. They studied coadaptive interpersonal dynamics in rugby union to model potential control parameter and collective variable relations in attacker–defender dyads. A videogrammetry analysis revealed how some agents generated fluctuations by adapting displacement velocity to create phase transitions and destabilize dyadic subsystems near the try line. Agent interpersonal dynamics exhibited characteristics of chaotic attractors and informational constraints of rugby union boxed dyadic systems into a low dimensional attractor. Data suggests that decisions and actions of agents in sports teams may be characterized as emergent, self-organizing properties, governed by laws of dynamical systems at the ecological scale. Further research needs to generalize this conceptual model of adaptive behavior in performance to other multiagent populations.     

The effect of facial attractiveness on temporal perception

Previous research suggests that feelings of fear, dislike, shame and sadness affect our perception of duration (Droit-Volet et al., 2004; Gil et al., 2009). The current study sought to expand our understanding of the variables which moderate temporal perception by examining whether the attractiveness of a face influenced its perceived duration. Participants completed a verbal estimation task in which they judged the duration of attractive, unattractive and neutral faces. The results showed that participants underestimated the duration of unattractive faces relative to attractive and neutral faces. Estimates of unattractive faces were also less accurate than those of the attractive and neutral faces. The results are consistent with Gil et al.'s (2009) suggestion that the duration of disliked stimuli are underestimated relative to liked and neutral stimuli because they detract attention from temporal perception. Analysis of the slope and intercept of the estimation gradients supports Zakay and Block's (1997) suggestion that reduced attention to time results in a multiplicative underestimation of duration.