Haptically creating affordances: the user-tool interface

Successful use of a hand-held tool requires overcoming the rotational inertia of the hand-plus-tool system. Where an object is grasped affects this rotational inertia. Appropriate choice of grip position may be crucial in the safe, effective, and efficient control of a hand-held tool. In 3 experiments, the authors investigated how choice of grip position on a tool was constrained by task demands. The results suggest that choice of grasp position serves to establish relationships among 3 variables derived from the inertial ellipsoid of the hand-object system (volume, symmetry, and eigenvector angle) in a way that specifically reflected the power or precision constraints of the given task. These variables have previously been shown to play a role in haptic perception of tool function. Changing grasp position on a tool is a way to exert control over the nuances of the user-tool interface.     

Perceiving the sweet spot

Many sports involve aligning a hitting implement with a ball trajectory such that contact is made at the implement's center of percussion or 'sweet spot'. This spot is not visibly distinct; its perception must be haptic. Although it is functionally defined with respect to contact--it is the point of impact that produces the least vibration in the hand holding the implement--hitting success requires appreciating the location of the sweet spot prior to contact. Two experiments verified that perceivers (novices as well as expert tennis players) distinguished perception of length from perception of the position of the sweet spot simply on the basis of wielding, both for tennis rackets and for bats contrived from wooden rods with attached masses. Results conformed to previous research on dynamic touch in showing that perceiving the lengths of wielded objects, including selectively perceiving partial lengths, is constrained by inertial properties of the object.     

Perceiving aperture size by striking

This study examined the ability to perceive surface separation on the basis of mechanical stimulation resulting from striking the surfaces' interiors with a hand-held rod. The variables manipulated were aperture size, angular displacement theta, distance b of the point of contact with the surfaces from the axis of rotation, hand-rod mass m, location of the hand-rod's center of mass a, and moment of inertia Io of the hand-rod. Given a particular rod and an aperture at a given distance, lambda = sin(theta/2)[1 - (2a/b) + (ma2/Io)] was invariant over explorations. Perception of aperture size was specific to lambda; it predicted successfully the interdependent effects of theta, b, and the mechanical properties of the implement. The results of 7 experiments were discussed in terms of the specificity of perception to information and the general ability to perceive distant things by means of body appendages.     

Using vision and dynamic touch to perceive the affordances of tools

The information that people use to perceive whether a tool is suitable for a certain task depends on what is available at a given time. Visually scanning a tool and wielding it each provide information about the functional attributes of the tool. In experiment 1, we investigated the relative contributions of vision and dynamic touch to perceiving the suitability of various tools for various tasks. The results show that, when both vision and dynamic touch are available, the visual information dominates. When limited to dynamic touch, ratings of suitability are constrained by the inertial properties of the tool, and the inertial properties that are exploited depend on the task. In experiment 2, we asked whether the manner in which a tool is manipulated in exploration depends on the task for which it is being evaluated. The results suggest that tools are manipulated in ways that reflect intentions to perceive particular affordances. Exploratory movements sometimes mimic performatory movements.     

Nonvisual judgment of the crossability of path gaps.

The ability of persons to locomote without vision with the aid of a hand-held probe was investigated in 4 experiments focusing on the negotiation of gaps in a pathway. In Experiment 1, Ss of extreme heights judged under sighted and blindfolded conditions whether gaps of different sizes could be crossed by walking. Crossability boundaries were lower for shorter Ss, but the height effect disappeared under normalization by leg length. Experiments 2-4 altered mechanical aspects of the probe (length and mass distribution) in the nonvisual case. Ss' performance was still reliable in each experiment, and their performances were constrained by parameters of the gap and of their action systems. Probe variables, however, had surprisingly little influence on the judgments of crossability. Results were discussed in terms of potential roles for information in different perceptual modalities.     

Perceiving the inertial properties of actions in anticipation skill

Inertial properties of throwing or striking actions constrain action outcomes, but their role in anticipation skill has not been investigated yet. Therefore, the aim of this study was to systematically investigate the effect of inertial constraints on anticipation skill. Fifteen semi-professional and fifteen novice soccer players were tasked with determining the kick direction of penalty kicks occluded at 160 ms, 80 ms before ball-foot contact, at ball-foot contact, or 80 ms after ball-foot contact. The inertial constraints were manipulated by loading the kicking leg with a 2.25 kg weight around the shank of the kicking leg and were compared with unloaded kicks. Anticipation accuracy of kick direction, response time, and decision confidence were recorded. It was found that loaded kick directions were anticipated more accurately, faster, and at earlier occlusion periods than unloaded kicks. The higher accuracy for the loaded kicks was found in the earlier occlusion conditions in experts compared to novices, as were the positive relationships between accuracy and confidence. It was concluded that the perception of the inertial constraints of the kicking action allowed for earlier anticipation of kick direction. It is proposed that accurate perception of the biomechanical property radius of gyrations in the body segments linking proximal to distal towards the kicking foot may provide this information.     

When constraints interact: a caution about reference variables,identification constraints,and scale dependencies in structural equation modeling

In traditional approaches to structural equations modeling, variances of latent endogenous variables cannot be specified or constrained directly and, consequently, are not identified, unless certain precautions are taken. The usual method for achieving identification has been to fix one factor loading for each endogenous latent variable at unity. An alternative approach is to fix variances using newer constrained estimation algorithms. This article examines the philosophy behind such constraints and shows how their appropriate use is neither as straightforward nor as noncontroversial as portrayed in textbooks and computer manuals. The constraints on latent variable variances can interact with other model constraints to interfere with the testing of certain kinds of hypotheses and can yield incorrect standardized solutions with some popular software.     

Simple and multiple P‐splines regression with shape constraints

In many research areas, especially within social and behavioural sciences, the relationship between predictor and criterion variables is often assumed to have a particular shape, such as monotone, single‐peaked or U‐shaped. Such assumptions can be transformed into (local or global) constraints on the sign of the nth‐order derivative of the functional form. To check for such assumptions, we present a non‐parametric regression method, P‐splines regression, with additional asymmetric discrete penalties enforcing the constraints. We show that the corresponding loss function is convex and present a Newton–Raphson algorithm to optimize. Constrained P‐splines are illustrated with an application on monotonicity‐constrained regression with both one and two predictor variables, using data from research on the cognitive development of children.     

Fitting the Reduced RUM with Mplus: A Tutorial

The Reduced Reparameterized Unified Model (Reduced RUM) is a diagnostic classification model for educational assessment that has received considerable attention among psychometricians. However, the computational options for researchers and practitioners who wish to use the Reduced RUM in their work, but do not feel comfortable writing their own code, are still rather limited. One option is to use a commercial software package that offers an implementation of the expectation maximization (EM) algorithm for fitting (constrained) latent class models like Latent GOLD or Mplus. But using a latent class analysis routine as a vehicle for fitting the Reduced RUM requires that it be re-expressed as a logit model, with constraints imposed on the parameters of the logistic function. This tutorial demonstrates how to implement marginal maximum likelihood estimation using the EM algorithm in Mplus for fitting the Reduced RUM.     

A Framework for Sustainability

Sustainability is value laden, and achieving sustainability is constrained by conflict and inefficient problem solving. Sustainability requires minimizing the costs of both constraints. This article outlines a framework for sustainability that recognizes divergent values, improves the productivity of debate, and suggests how to reduce sustainability costs.     

Thinking Inside the Tool Box: Creativity,Constraints, and the Colossal Portraits of Chuck Close

This article presents a problem‐solving model to examine the often problematic relationship between expertise and creativity. The model has two premises, each the opposite of a common cliché. The first cliché asserts that creativity requires thinking outside‐the‐box. The first premise argues that experts can only think and problem solve inside the tool boxes of their expertise. The second cliché, that creativity requires freedom from constraints, points to the problem with expertise. Free to do anything, experts repeat what has worked best in the past. A solution is suggested by the second premise: to circumvent the liabilities of expertise, creativity requires constraints of a particular paired kind. The model is introduced as an expansion of prior process models focused on problem identification and construction. Problem‐finding is reanalyzed as constraint‐finding. A case study shows how one recognized creator, painter Chuck Close, uses constraints as a tool to solve the expertise‐creativity problem.     

Detection of informational constraints related to multi-variate visual displays

A contingent uncertainty of one bit is perceptible when imposed upon a combination of two binary-coded visual display variables, but not when imposed upon a combination of three variables. Why? The limitation may be sought in the average amount of the constraint, in the form of the constraint, or in the particular selection of display variables. Tests were carried out in which apparently equivalent informational constraints were imposed upon a single display variable. Such constraints were highly discriminable. Further tests reveal that the limiting feature for the detection of multi-variate constraints is probably the mean constraint level, averaged over all display elements, rather than the constraint level imposed upon the constrained display elements.     

Gods,Animals, and Artists: Some Problem Cases in Herder's Philosophy of Language

Theories in the behavioral sciences are constrained so that stated relationships are empirically testable and explanations have predictive power. These constraints constitute the classical paradigm, and are trivial just when ‘causal relationships’ do not hold. It appears that such relationships do not hold for linguistic, and presumably other, behaviors, thus precluding study within the classical paradigm. This compels study of those behaviors in terms of the non‐traditional approach to testability and explanation developed in Chomskyan linguistics. These constitute the grammatical paradigm. The existence of two paradigms requires that any inquiry begin by determining which paradigm is appropriate.     

A prior predictive loss function for the evaluation of inequality constrained hypotheses

In many types of statistical modeling, inequality constraints are imposed between the parameters of interest. As we will show in this paper, the DIC (i.e., posterior Deviance Information Criterium as proposed as a Bayesian model selection tool by Spiegelhalter, Best, Carlin, & Van Der Linde, 2002) fails when comparing inequality constrained hypotheses. In this paper, we will derive the prior DIC and show that it also fails when comparing inequality constrained hypotheses. However, it will be shown that a modification of the prior predictive loss function that is minimized by the prior DIC renders a criterion that does have the properties needed in order to be able to compare inequality constrained hypotheses. This new criterion will be called the Prior Information Criterion (PIC) and will be illustrated and evaluated using simulated data and examples. The PIC has a close connection with the marginal likelihood in combination with the encompassing prior approach and both methods will be compared. All in all, the main message of the current paper is: (1) do not use the classical DIC when evaluating inequality constrained hypotheses, better use the PIC; and (2) the PIC is considered a proper model selection tool in the context of evaluating inequality constrained hypotheses.     

The use of computer-controlled video disks in the study of spatial learning

The empirical study of spatial learning has been constrained by a range of methodological and technical limitations. Part of these are due to constraints in the stimulus delivery systems for pictorial displays that are available to the researcher. Surrogate travel systems—based on model photography, off-line computer graphics, and on-line computer graphics—provide alternative research settings. Yet none of the systems provides for both detailed displays and ease of subject interaction, both of which prove important in the investigation of spatial learning. Computer-controlled video-disk systems do allow both detail and interaction, therefore providing a research tool in which spatial learning phenomena can be observed carefully. A pilot study of spatial learning using a video-disk system is briefly described to demonstrate the sorts of phenomena observable with such a system.     

Constrained k‐means on cluster proportion and distances among clusters for longitudinal data analysis

Clustering individuals by measures of similarity or dissimilarity at trajectories of changes in longitudinal data enables determination of typical patterns of development and growth. The present research proposes a new constrained k‐means method with lower bound constraints on cluster proportions and distances among clusters at focused variables and time points to fulfill various needs in clustering longitudinal data. The method assumes a large number of clusters at the onset and iteratively deletes and combines clusters according to these constraints. An additional property of the proposed constrained k‐means includes direct estimation of the unknown number of clusters. Simulation results clearly show the usefulness of the method for extracting clusters in plausible, real‐life analysis including non‐normality within clusters, and the proposed algorithm works well and convergence of the estimates is satisfactory. An actual example using Japanese longitudinal data regarding sleep habits and mental health is presented to verify the utility of the proposed constrained k‐means.     

Time course of planning for object and action parameters in visually guided manipulation

Under visual guidance, subjects reached for and manipulated an object that variedin weight and surface texture (slipperiness). The manipulatory action was either grasping, lifting, or posting in a slot. The task was constrained or unconstrained with respect to speed, grasp pattern, and contact force. Initiation time (pre-reach), movement time (reach), and post-contact errors were measured, to examine planning for task performance at three points in time. Results indicate that in the constrained task, the manipulatory action was planned during the initiation time, but planning for object parameters was deferred until the reach interval. With relaxed task constraints, initiation times increased,and texture and manipulatory action had independent effects on premovement planning. Errors were affected interactively by all variables. The results suggest a planning process that unfolds over time, incorporating in turn the manipulatory action, object texture, and object weight. This unfolding accommodates variables proximate to the time where they will affect physical action.     

Estimation of nonlinear mixed-effects continuous-time models using the continuous-discrete extended Kalman filter

Many intensive longitudinal measurements are collected at irregularly spaced time intervals, and involve complex, possibly nonlinear and heterogeneous patterns of change. Effective modelling of such change processes requires continuous-time differential equation models that may be nonlinear and include mixed effects in the parameters. One approach of fitting such models is to define random effect variables as additional latent variables in a stochastic differential equation (SDE) model of choice, and use estimation algorithms designed for fitting SDE models, such as the continuous-discrete extended Kalman filter (CDEKF) approach implemented in the dynr R package, to estimate the random effect variables as latent variables. However, this approach's efficacy and identification constraints in handling mixed-effects SDE models have not been investigated. In the current study, we analytically inspect the identification constraints of using the CDEKF approach to fit nonlinear mixed-effects SDE models; extend a published model of emotions to a nonlinear mixed-effects SDE model as an example, and fit it to a set of irregularly spaced ecological momentary assessment data; and evaluate the feasibility of the proposed approach to fit the model through a Monte Carlo simulation study. Results show that the proposed approach produces reasonable parameter and standard error estimates when some identification constraint is met. We address the effects of sample size, process noise variance, and data spacing conditions on estimation results.     

The effects of cueing and constraint instructions on children's free recall performance

The performance of nursery school children was investigated in two experiments involving cued and constrained free recall. Under constrained instructions, subjects were required to recall items by category. Under cued instructions subjects could recall items in any order they wished but the organized nature of the lists was identified and subjects were told that they would remember more if they recalled things from the same category together. No effects of cueing instructions were obtained in either Experiment I or Experiment II. Constrained recall instructions led to enhanced recall and category clustering. However, the beneficial effects were not maintained on later trials with the same list or on a transfer list when the constraints on recall were dropped. In addition, the introduction of constrained recall instructions had identical effects whether they were introduced early or late in practice. The results were discussed in terms of the influences of variables which affect the subjects' use of retrieval strategies and the development of memory.     

Selection of gait parameters during constrained walking

It is commonly thought that at prescribed speeds humans choose gait parameters that minimize the cost of transportation. However, it is unclear whether and how the relationship between step length and step frequency is affected by the additional physiological factors caused by constraints. We performed a series of experiments to understand the selection of gait parameters under different constraints from a probabilistic perspective. First, we show that the effect of constraining step length on step frequency (i.e., monotonically decrease, Experiment I) is different from the effect of constraining step frequency on step length (i.e., inverted-U, Experiment II). Using the results from Experiment I and II, we summarized the marginal distribution of step length and step frequency and built their joint distribution in a probabilistic model. The probabilistic model predicts the selection of gait parameters by achieving the maximum probability of joint distribution of step length and step frequency. In Experiment III, the probabilistic model could well predict gait parameters at prescribed speeds, and it is similar to minimizing the cost of transportation. Finally, we show that the distribution of step length and step frequency were completely different between constrained and non-constrained walking. We argue that constraints in walking are major factors determining how humans choose gait parameters due to their involvement of mediators, i.e., attention or active control. Using the probabilistic model to account for gait parameters has an advantage compared with fixed-parameter models in that it can still include the effect of hidden mechanical, neurophysiological, or psychological variables by grouping them into distribution curves.