Archive for the ‘Publications’ Category

Time Delay Embedding Increases Estimation Precision of Models of Intraindividual Variability

Monday, December 17th, 2012

Oertzen, T. v. & Boker, S. (2010) Time Delay Embedding Increases Estimation Precision of Models of Intraindividual Variability. Psychometrika, 75:1, 158-175. NIHMS ID: 427398

This paper investigates the precision of parameters estimated from local samples of time dependent functions. We find that time delay embedding, i.e., structuring data prior to analysis by constructing a data matrix of overlapping samples, increases the precision of parameter estimates and in turn statistical power compared to standard independent rows of panel data. We show that the reason for this effect is that the sign of estimation bias depends on the position of a misplaced data point if there is no a priori knowledge about initial conditions of the time dependent function. Hence, we reason that the advantage of time delayed embedding is likely to hold true for a wide variety of functions. We support these conclusions both by mathematical analysis and two simulations.

The manuscript of this article accepted for publication can be downloaded as a PDF. This article may not exactly replicate the final version published in Psychometrika. It is not the copy of record.

Modeling Noisy Data with Differential Equations using Observed and Expected Matrices

Tuesday, March 23rd, 2010

Deboeck, P. R. & Boker, S. M. (in press) Modeling Noisy Data with Differential Equations using Observed and Expected Matrices. Psychometrika

Complex intraindividual variability observed in psychology may be well described using differential equations. It is difficult, however, to apply differential equation models in psychological contexts, as time series are frequently short, poorly sampled, and have large proportions of measurement and dynamic error. Furthermore, current methods for differential equation modeling usually consider data that are atypical of many psychological applications. Using embedded and observed data matrices, a statistical approach to differential equation modeling is presented. This approach appears robust to many characteristics common to psychological time series.

The manuscript of this article accepted for publication can be requested as a pdf file from the first author: Pascal Deboeck at University of Kansas.

Resilience-As-Process: Negative Affect, Stress, and Coupled Dynamical Systems

Tuesday, March 23rd, 2010

Montpetit, M. A., Bergeman, C. S., Deboeck, P. R., Tiberio, S. S., & Boker, S. M. (2010) Resilience-As-Process: Negative Affect, Stress, and Coupled Dynamical Systems. Psychology and Aging 25:3, 631-640

This article describes a link between stress and negative affect as a system of coupled linear differential equations. The idea is basically that stress and negative affect are coupled, but that those individuals with higher trait resilience scores would experience stress as being less coupled to changes in negative affect. In addition it was found that higher levels of social support resulted in greater damping of the fluctuations in negative affect and decreased coupling between stress and negative affect.

The manuscript of this article accepted for publication can be requested as a pdf file from the first author: Mignon Montpetit at Illinois Wesleyan University.

Issues in Intraindividual Variability: Individual Differences in Equilibria and Dynamics over Multiple Time Scales

Tuesday, October 6th, 2009

Boker, S. M., Molenaar, P., & Nesselroade, J. R. (in press) Issues in Intraindividual Variability: Individual Differences in Equilibria and Dynamics over Multiple Time Scales. Psychology and Aging

This article expands on three methodological issues that address needs required to improve research in intraindividual variability: (1) The need to consider the relationship between the time scale of a process and the time scale of its measurement, (2) The need to first model both the deterministic and the stochastic components of psychological processes at the intraindividual level then at a second level model the variation in these deterministic and stochastic components in samples of individuals, and (3) The need to expand one’s thinking beyond individual differences in variance and covariance of latent variables given measurement invariance in order to consider the opposite possibility: idiosyncratic measurement models with invariance applied to the variance and covariance of latent variables.

The manuscript of this article accepted for publication can be downloaded as a PDF. This article may not exactly replicate the final version published in the APA journal. It is not the copy of record.

Parallel Workflows for Data Driven Structural Equation Modeling in Functional Neuroimaging

Tuesday, October 6th, 2009

Kenny, S., Andric, M., Boker, S. M., Neale, M. C., Wilde, M., & Small, S. L. (2009) Parallel Workflows for Data–Driven Structural Equation Modeling in Functional Neuroimaging. Frontiers in Neuroscience

This article presents a computational framework suitable for a data-driven approach to structural equation modeling (SEM) and describe several workflows for modeling functional magnetic resonance imaging (fMRI) data within this framework. The Computational Neuroscience Applications Research Infrastructure (CNARI) employs a high-level scripting language called Swift, which is capable of spawning hundreds of thousands of simultaneous R processes (R Core Development Team, 2008), consisting of self-contained structural equation models, on a high performance computing system (HPC). These self-contained R processing jobs are data objects generated by OpenMx, a plug-in for R, which can generate a single model object containing the matrices and algebraic information necessary to estimate parameters of the model. With such an infrastructure in place a structural modeler may begin to investigate exhaustive searches of the model space. Specific applications of the infrastructure, statistics related to model fit, and limitations are discussed in relation to exhaustive SEM. In particular, we discuss how workflow management techniques can help to solve large computational problems in neuroimaging.

Frontiers in Neuroscience is an open-access journal, so a PDF of the article can be downloaded for free.

Resilience in Adulthood Comes of Age

Tuesday, October 6th, 2009

Ong, A. D., Bergeman, C. S., & Boker, S. M. (2009) Resilience in Adulthood Comes of Age: Defining Features and Dynamic Conceptions. Journal of Personality. 77:6.

This article begins with a selective review of the broad literature on resilience, giving emphasis to the major approaches, empirical findings, and guiding principles that characterize prior studies. It then summarizes an approach to the phenomenon of resilience and illustrate select parts of previous and ongoing studies of older adults. Findings from this research add to the growing body of empirical evidence suggesting that resilience is a common phenomenon that emerges from the coordinated orchestration of basic human adaptive processes.

This article is previewed on the Journal of Personality website and will appear in the December issue. Unfortunately, Wiley/Blackwell rules would require us to pay at $3,000 fee if we were to either provide a downloadable copy or send a pdf as a response to a reprint request. However, since NIH funded parts of this work, Wiley/Blackwell is required to submit the final published version to pubmed. Hooray for NIH! When the free pubmed version is available, a link to that version will appear here.

Representing Time-Varying Cyclic Dynamics Using Multiple-Subject State-Space Models

Thursday, September 17th, 2009

Chow, S.-M., Hamaker, E. L., Fujita, F. & Boker, S. M. (2009) Representing Time-Varying Cyclic Dynamics Using Multiple-Subject State-Space Models. British Journal of Mathematical and Statistical Psychology. vol 62, 683-716.

THis article compares two contemporary state-space models for dynamical systems analysis: the stochastic cycle model and the dynamic harmonic regression model. These models are applied to two studies: one on postural dynamics and another daily diary study of affect. Publication rules for BJMSP prohibit us from quoting excerpts or distributing the manuscript on the web, but we can send a reprint if you send one of the authors an email request.

Get The FACS Fast

Wednesday, September 16th, 2009

Brick, T.R., Hunter, M.D., & Cohn, J.F. Get The FACS Fast: Automated FACS face analysis benefits from the addition of velocity. 2009 International Conference on Affective Computing & Intelligent Interaction (ACII 2009)

This article reports that the accuracy of automatic recognition of FACS codes from video data can be improved by including velocity and acceleration of tracked points on faces from the Cohn-Kanade database.

The article can be downloaded as a PDF.

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Effects of Damping Head Movement and Facial Expression in Dyadic Conversation Using Real-Time Facial Expression Tracking and Synthesized Avatars

Thursday, July 9th, 2009

Boker, S. M., Cohn, J. F., Theobald, B.-J., Matthews, I., Brick, T. & Spies, J. (in press) Effects of Damping Head Movement and Facial Expression in Dyadic Conversation Using Real-Time Facial Expression Tracking and Synthesized Avatars. Philosophical Transactions of the Royal Society B.

This article reports an experiment in which research assistants’ head movements and facial expressions were motion tracked during videoconference conversations, an avatar face was reconstructed in real time, and naive participants spoke with the avatar face. Research assistants’ facial expressions, vocal inflections, and head movements were attenuated at one minute intervals in a fully crossed experimental design. Attenuated head movements led to increased head nods and lateral head turns, and attenuated facial expressions led to increased head nodding in both naive participants and in confederates. The results are consistent with a hypothesis that the dynamics of head movements in dyadic conversation include a shared equilibrium.

(a) four facial expression (b) four attenuated facial expression.

The manuscript of this article accepted for publication can be downloaded as a PDF. This preprint may not exactly replicate the final version published in the journal. It is not the copy of record.

Time Delay Embedding Increases Estimation Precision of Models of Intraindividual Variability

Wednesday, July 1st, 2009

von Oertzen, T. & Boker, S. (in press) Time Delay Embedding Increases Estimation Precision of Models of Intraindividual Variability. Psychometrika

An article describing a surprising result for estimating dynamical systems models was recently accepted for publication by Psychometrika. Publication rules for Psychometrika prohibit us from quoting excerpts or distributing the manuscript on the web, but we can send a preprint if you send one of the authors an email request.