Papers by Timo Von Oertzen
Stochastic resonance (SR) is fundamental to physical and biological processes. Here, we use a sto... more Stochastic resonance (SR) is fundamental to physical and biological processes. Here, we use a stochastic gain-tuning model to investigate interactions between aging-related increase of endogenous neuronal noise and external input noise in affecting SR. Compared to networks that have optimal system gain parameter of the activation function, networks with attenuated endogenous gain tuning at the system level, simulating aging neurocognitive
Computing Research Repository, 2010
We study techniques for deciding the computational complexity of infinite-domain constraint satis... more We study techniques for deciding the computational complexity of infinite-domain constraint satisfaction problems. For certain fundamental algebraic structures Delta, we prove definability dichotomy theorems of the following form: for every first-order expansion Gamma of Delta, either Gamma has a quantifier-free Horn definition in Delta, or there is an element d of Gamma such that all non-empty relations in Gamma contain
In this paper, we give a PSPACE-completeness reduction from QBF to the Dyson Telescopes Puzzle wh... more In this paper, we give a PSPACE-completeness reduction from QBF to the Dyson Telescopes Puzzle where opposing telescopes can overlap in at least two spaces. The reduction does not use tail ends of telescopes or initially partially extended telescopes. If two opposing telescopes can overlap in at most one space, we can solve the puzzle in polynomial time by a
NeuroImage, 2015
Please cite this article as: Karch, Julian D., Sander, Myriam C., von Oertzen, Timo, Brandmaier, ... more Please cite this article as: Karch, Julian D., Sander, Myriam C., von Oertzen, Timo, Brandmaier, Andreas M., Werkle-Bergner, Markus, Using within-subject pattern classification to understand lifespan age differences in oscillatory mechanisms of working memory selection and maintenance, NeuroImage (2015),
Frontiers in Psychology, 2015
Researchers planning a longitudinal study typically search, more or less informally, a multivaria... more Researchers planning a longitudinal study typically search, more or less informally, a multivariate space of possible study designs that include dimensions such as the hypothesized true variance in change, indicator reliability, the number and spacing of measurement occasions, total study time, and sample size. The main search goal is to select a research design that best addresses the guiding questions and hypotheses of the planned study while heeding applicable external conditions and constraints, including time, money, feasibility, and ethical considerations. Because longitudinal study selection ultimately requires optimization under constraints, it is amenable to the general operating principles of optimization in computer-aided design. Based on power equivalence theory (MacCallum et al., 2010; von Oertzen, 2010), we propose a computational framework to promote more systematic searches within the study design space. Starting with an initial design, the proposed framework generates a set of alternative models with equal statistical power to detect hypothesized effects, and delineates trade-off relations among relevant parameters, such as total study time and the number of measurement occasions. We present LIFESPAN (Longitudinal Interactive Front End Study Planner), which implements this framework. LIFESPAN boosts the efficiency, breadth, and precision of the search for optimal longitudinal designs. Its initial version, which is freely available at http://www.brandmaier.de/lifespan, is geared toward the power to detect variance in change as specified in a linear latent growth curve model.
The goal of the present study was to select a set of highly imaginable and concrete words that ca... more The goal of the present study was to select a set of highly imaginable and concrete words that can be used in age-comparable memory research. The selection process included two steps. First, 10 children aged 7-9 years rated 400 high-imagery, concrete, and meaningful words selected from an existing corpus of 1082 spoken words on a threepoint scale of comprehensibility. Second, two independent raters further selected words to reduce the likelihood of lexical error during recall. As a result, 413 words were retained as stimulus materials for age-comparative investigations of episodic memory performance.
Proceedings of the 5th Nordic conference on Human-computer interaction building bridges - NordiCHI '08, 2008
Abstract In this work we propose an extension of our laboratory evaluation framework [1] equipped... more Abstract In this work we propose an extension of our laboratory evaluation framework [1] equipped with a virtual environment (VE). In order to simulate ecologically valid walking in the VE, we evaluate biomechanical processes in gait to control the speed of the treadmill that participants in the laboratory are walking on. Our approach allows predicting the actual speed while walking based on hip movement and additionally on step length. In order to validate our approach we present preliminary results from a study comparing different ...
Cognitive Technologies, 2010
Lifespan CognitionMechanisms of Change, 2006
Automata, Languages and Programming, 2009
We study logical techniques for deciding the computational complexity of infinite-domain constrai... more We study logical techniques for deciding the computational complexity of infinite-domain constraint satisfaction problems (CSPs). For the fundamental algebraic structure G</font > = (\mathbb R; L1,L2,...)\Gamma=(\mathbb R; L_1,L_2,\dots) where \mathbb R\mathbb R are the real numbers and L 1,L 2,... is an enumeration of all linear relations with rational coefficients, we prove that a semilinear relation R (i.e., a relation
We demonstrate that common genetic polymorphisms contribute to the increasing heterogeneity of co... more We demonstrate that common genetic polymorphisms contribute to the increasing heterogeneity of cognitive functioning in old age. We assess two common Val/Met polymorphisms, one affecting the Catechol-O-Methyltransferase (COMT) enzyme, which degrades dopamine (DA) in prefrontal cortex (PFC), and the other infl uencing the brain-derived neurotrophic factor (BDNF) protein. In two tasks (Wisconsin Card Sorting and spatial working memory), we fi nd that effects of COMT genotype on cognitive performance are magnifi ed in old age and modulated by BDNF genotype. Older COMT Val homozygotes showed particularly low levels of performance if they were also BDNF Met carriers. The age-associated magnifi cation of COMT gene effects provides novel information on the inverted U-shaped relation linking dopaminergic neuromodulation in PFC to cognitive performance. The modulation of COMT effects by BDNF extends recent evidence of close interactions between frontal and medial-temporal circuitries in executive functioning and working memory.
Lecture Notes in Computer Science, 2004
A regular language L is called dense if the fraction f m of words of length m over some fixed sig... more A regular language L is called dense if the fraction f m of words of length m over some fixed signature that are contained in L tends to one if m tends to infinity. We present an algorithm that computes the number of accumulation points of (f m ) in polynomial time, if the regular language L is given by a finite deterministic automaton, and can then also efficiently check whether L is dense. Deciding whether the least accumulation point of (f m ) is greater than a given rational number, however, is coNP-complete. If the regular language is given by a non-deterministic automaton, checking whether L is dense becomes PSPACE-hard. We will formulate these problems as convergence problems of partially observable Markov chains, and reduce them to combinatorial problems for periodic sequences of rational numbers.
Theoretical Computer Science, 2009
We systematically investigate the computational complexity of constraint satisfaction problems fo... more We systematically investigate the computational complexity of constraint satisfaction problems for constraint languages over an infinite domain. In particular, we study a generalization of the well-established notion of maximal constraint languages from finite to infinite domains. If the constraint language can be defined with an ω-categorical structure, then maximal constraint languages are in one-to-one correspondence to minimal oligomorphic clones. Based on this correspondence, we derive general tractability and hardness criteria for the corresponding constraint satisfaction problems.
Psychometrika, 2010
This paper investigates the precision of parameters estimated from local samples of time dependen... more 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. 159 design has the advantage of a large sample of individuals, and thus the standard error of the mean within-person time series coefficient may be small. In this example design, 1,000 observations were made: 5 observations on each of 200 individuals.
Psychology and Aging, 2011
In cross-sectional age variance extraction (CAVE), age, the indicator of a hypothesized developme... more In cross-sectional age variance extraction (CAVE), age, the indicator of a hypothesized developmental mechanism, and a developmental outcome are specified as independent, mediator, and target variables, respectively, to test hypotheses about behavioral development. We show that: (a) longitudinal change in a mediator variable accounting for substantial cross-sectional age-related variance in the target variable need not correlate with the target variable's longitudinal change; and, conversely, (b) longitudinal change in a mediator not sharing cross-sectional age-related variance with the target variable may nevertheless correlate highly with that variable's longitudinal change. We discourage use of CAVE for testing multivariate hypotheses about behavioral development.
Psychology and Aging, 2008
The authors examined life-span differences in the maintenance of skilled episodic memory performa... more The authors examined life-span differences in the maintenance of skilled episodic memory performance by assessing 100 individuals (10 -11, 12-13, 21-26, and 66 -79 years old) 11 months after termination of an intensive multisession mnemonic training program (Y. Brehmer, S.-C. Li, V. Müller, T. von . Skill maintenance was tested in 2 follow-up sessions, the first without and the second with mnemonic reinstruction. Younger and older adults' average performance levels were stable across time. In contrast, both younger and older children's memory performance improved beyond originally attained levels. Older adults' performance improved from the first to the second follow-up session, presumably profiting from instruction-induced skill reactivation. Results suggest that (a) skill maintenance is largely intact in healthy older adults, (b) older adults need environmental support to fully reactivate their former skill levels (cf. F. I. M. , and (c) children adapt a skill learned 11 months ago to their increasing cognitive capabilities.
Psychology and Aging, 2013
Structural equation models have become a broadly applied data-analytic framework. Among them, lat... more Structural equation models have become a broadly applied data-analytic framework. Among them, latent growth curve models have become a standard method in longitudinal research. However, researchers often rely solely on rules of thumb about statistical power in their study designs. The theory of power equivalence provides an analytical answer to the question of how design factors, for example, the number of observed indicators and the number of time points assessed in repeated measures, trade off against each other while holding the power for likelihood-ratio tests on the latent structure constant. In this article, we present applications of power-equivalent transformations on a model with data from a previously published study on cognitive aging, and highlight consequences of participant attrition on power.
Psychological Methods, 2006
We evaluated the statistical power of single-indicator latent growth curve models (LGCMs) to dete... more We evaluated the statistical power of single-indicator latent growth curve models (LGCMs) to detect correlated change between two variables (covariance of slopes) as a function of sample size, number of longitudinal measurement occasions, and reliability (measurement error variance). Power approximations following the method of Satorra and Saris were used to evaluate the power to detect slope covariances. Even with large samples (N ϭ 500) and several longitudinal occasions (4 or 5), statistical power to detect covariance of slopes was moderate to low unless growth curve reliability at study onset was above .90. Studies using LGCMs may fail to detect slope correlations because of low power rather than a lack of relationship of change between variables. The present findings allow researchers to make more informed design decisions when planning a longitudinal study and aid in interpreting LGCM results regarding correlated interindividual differences in rates of development.
PLoS ONE, 2012
Interest in the effects of sleeping behavior on health and performance is continuously increasing... more Interest in the effects of sleeping behavior on health and performance is continuously increasing-both in research and with the general public. Ecologically valid investigations of this research topic necessitate the measurement of sleep within people's natural living contexts. We present evidence that a new approach for ambulatory accelerometry data offers a convenient, reliable, and valid measurement of both people's sleeping duration and quality in their natural environment. Ninety-two participants (14-83 years) wore acceleration sensors on the sternum and right thigh while spending the night in their natural environment and following their normal routine. Physical activity, body posture, and change in body posture during the night were classified using a newly developed classification algorithm based on angular changes of body axes. The duration of supine posture and objective indicators of sleep quality showed convergent validity with self-reports of sleep duration and quality as well as external validity regarding expected age differences. The algorithms for classifying sleep postures and posture changes very reliably distinguished postures with 99.7% accuracy. We conclude that the new algorithm based on body posture classification using ambulatory accelerometry data offers a feasible and ecologically valid approach to monitor sleeping behavior in sizable and heterogeneous samples at home.
Neurocomputing, 2006
Stochastic resonance (SR) is fundamental to physical and biological processes. Here, we use a sto... more Stochastic resonance (SR) is fundamental to physical and biological processes. Here, we use a stochastic gain-tuning model to investigate interactions between aging-related increase of endogenous neuronal noise and external input noise in affecting SR. Compared to networks that have optimal system gain parameter of the activation function, networks with attenuated endogenous gain tuning at the system level, simulating aging neurocognitive systems with more intrinsic neuronal noise but less plasticity, continue to exhibit the general SR effect; however, this effect is smaller and requires more external noise. This set of finding suggests that determining the optimal proportion of resonance-inducing external noise as a function of internal-system stochastic gain tuning properties promotes unified theorizing about sensory and cognitive aging at behavioral and neural levels of analysis. r
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Papers by Timo Von Oertzen