Showing papers by "Tilburg University published in 1984"

The Relationship between Learning Conception, Study Strategy and Learning Outcome.

Abstract: Summary. The essential point of the present study is that human learning should be studied from a second-order perspective. This means that the emphasis is on how people see and understand the world around them. Attention is given to the ways in which students tackle the studying of a text, using the distinction introduced by Marton and Saljo between a deep-level and a surface-level approach. Also investigated is the extent to which these study strategies can be related to the views of students on learning itself (learning conceptions) and the quality of the learning outcome. It turned out that a learning outcome of relatively high quality must be especially associated with deep-level approach and a constructive learning conception.

Polynomial Algorithms for Perfect Graphs

Abstract: We show that the weighted versions of the stable set problem, the clique problem, the coloring problem and the clique covering problem are solvable in polynomial time for perfect graphs. Our algorithms are based on the ellipsoid method and a polynomial time separation algorithm for a certain class of positive semidefinite matrices related to Lovasz's bound θ(G) on the Shannon capacity of a graph. We show that θG) can be computed in polynomial time for all graphs G and also give a new characterization of perfect graphs in terms of this number θ(G). In addition we prove that the problem of verifying that a graph is imperfect is in NP. Moreover, we show that the computation of the stability number and the fractional stability number of a graph are unrelated with respect to hardness (if P ≠NP).

Chapter 23 Latent variable models in econometrics

Abstract: Publisher Summary This chapter discusses latent variable models in econometrics. The essential characteristic of a latent variable is revealed by the fact that the system of linear structural equations in which it appears cannot be manipulated so as to express the variable as a function of measured variables only. It discusses that for a linear structural equation system to be called “latent variable model,” there is at least one more independent variable than the number of measured variables. Usage of the term “independent” variable as contrasted with “exogenous” variable, the more common phrase in econometrics, includes measurement errors and the equation residuals themselves. In the functional model, the true values of exogenous variables are fixed variates, and therefore, are best thought of as nuisance parameters that may have to be estimated en route to getting consistent estimates of the primary structural parameters of interest. Finally, restrictions on a model's covariance structure, which are commonplace in sociometric and psychometric modeling, also serve to aid identification.

Movement-associated potentials and motor control. Report of the EPIC VI Motor Panel.

Abstract: The entirety of human behavior is based on motor acts. Without some kind of motor expression no reasoning or tradition could be retained in the culture. Man's capacity for acting on and interacting with the environment is dependent on his voluntary movements. Although investigations into human sensory information processing are numerous and have a long history, comparably fewer studies have been devoted to the analysis of human cortical motor functions. Previous views of human cortical motor control, determined by the sequelae of cerebral stroke and cortical stimulation experiments, envisaged an exclusively contralateral organization. However, the processes underlying early preparation for voluntary movement are different. Readiness for movement is accompanied by a widespread slow negativity over both hemispheres, the Bereitschaftspotential (BP, Kornhuber and Deecke, 1964, 1965). There are basically two major categories of movements, the distinction being made by how the movements are initiated. Movements can occur in response to an external stimulus. Movements of this kind are reactions to our environment. But we can also move spontaneously, i.e. of our own volition. Movements of this kind are our free actions on the environment. Although we also need motivation to react to an external

Corrigendum to our paper “the ellipsoid method and its consequences in combinatorial optimization”

Abstract: An error in the proof, and in the statement of a generalization, of the result that submodular setfunctions can be minimized over the subsets with odd cardinality is corrected.

Influence of motor unit firing statistics on the median frequency of the EMG power spectrum

Abstract: Changes in the EMG power spectrum during static fatiguing contractions are often attributed to changes in muscle fibre action potential conduction velocity. Mathematical models of the EMG power spectrum, which have been empirically confirmed, predict that under certain conditions a distinct maximum occurs in the low-frequency part of the spectrum, indicating the dominant firing rate of the motor units. The present study investigated the influence of this firing rate peak on the spectral changes during a static fatiguing contraction at 50% of maximum EMG amplitude in the frontalis and corrugator supercilii muscles. An exponential decrease of the median frequency (MF) of the EMG power spectrum was observed when the firing rate peak was absent. When the firing rate peak was present, an exaggerated decrease of MF in the beginning of the contraction was found, which was associated with an increase in firing rate peak magnitude. In later stages of the contraction, a partial recovery of MF occurred, concomitant with a decrease in firing rate peak magnitude. The influence of the firing rate peak on MF was also investigated during nonfatiguing contractions of the frontalis muscle at 20, 40, 60, and 80% of maximum EMG amplitude. A curvilinear relationship between MF and contraction strength was found, whether firing rate peaks were present or absent. The presence of firing rate peaks, however, was associated with a decrease in MF which was inversely related to contraction strength, due to the inverse relationship between firing rate peak magnitude and contraction strength.

Type A behaviour and self-reports of coping preferences.

Abstract: Three hundred male subjects (age range 25–40) completed both the Dutch version of the Jenkins Activity Survey (JAS) and a revised version of the Ways of Coping Checklist (WCC). Principal component analysis on the WCC yielded six factors with eigenvalues above 2.0: 1 'wishful thinking/escape'; 2 'acceptance'; 3 'problem-focused/help-seeking'; 4 'withholding'; 5 'self-blame'; and 6 'growth'. Factor scores for each factor were averaged and compared between Type As and Type Bs. Type A scores were lower on 'acceptance', but higher on 'problem-focused/help-seeking' and 'self-blame'. These results favour the conclusion that Type As, when confronted with stressful situations, are more prone to active, problem-focused behaviour, do not acquiesce in the problems, and see themselves, rather than the environment, as the cause of their problems.

Amplitude and Bandwidth of the Frontalis Surface EMG: Effects of Electrode Parameters

Abstract: In the present investigation, the frontalis surface EMG was differentially recorded during static voluntary submaximal contractions. First, mean rectified EMG (MREMG) and EMG signal bandwidth were examined for two different bilateral EMG derivations (superior and inferior) with the electrodes placed in horizontal direction and two unilateral derivations (left and right) with the electrodes placed in vertical direction. MREMG was significantly different between the four derivations but absolute differences were small. Bandwidth also varied significantly with derivation. Second, the influence of inter-electrode distance and electrode size was examined for unilateral derivations. The influence of inter-electrode distance on MREMG was significant but the absolute effect was marginal. We suggest that a clear effect is to be expected only within the range of small distances (smaller than 10 mm). The significant effect disappeared when MREMG was expressed as proportion of the MREMG during maximal contraction. This normalization seems to allow better intra-individual or inter-individual comparisons of integrated EMG, especially when different recording methods are used. The influence of inter-electrode distance on bandwidth was not significant. Electrode size had no significant influence on MREMG and bandwidth. EMG power spectra indicated that integrated frontalis EMG can be validly measured only when using recording equipment with a frequency response of 5–500 Hz.

Specification of direction and duration during programming of discrete sliding movements

Abstract: Two experiments on duration programming of a discrete sliding movement in choice reactions are reported. In the first experiment it was examined whether duration of movement might be preprogrammed when varied across sessions. The result suggested that programming of movement duration is dependent on direction uncertainty. Experiment 2 used the movement precue technique in an attempt to further examine programming of movement duration and direction. Movement duration, movement direction, movement form and foreperiod duration were manipulated. When duration was not precued, a duration effect was found, while precueing resulted in disappearance of the duration effect, demonstrating that duration of sliding movements can be preprogrammed. Moreover, (pre)programming duration was independent of direction uncertainty, supporting an independent order notion of programming of these response variables. Evidence that motor preparation comprises different processing stages was derived from the additive effects of foreperiod duration and of the movement variables duration and direction.

A polynomial-time test for total dual integrality in fixed dimension

Abstract: In this note we show that, for any fixed number r, there exists a polynomial-time algorithm to test whether a given system of linear inequalities Ax≤b is totally dual integral, where A is an integer matrix of rank r.

Cardiac-somatic coupling during the foreperiod in a simple reaction-time task.

Abstract: The cardiac-somatic coupling hypothesis predicts a phasic decrease of general somatic behavior concomitant with a phasic heart-rate deceleration. This hypothesis was investigated during a constant 4 s foreperiod (FP) in a simple auditory reaction-time task. Intertrial interval duration was variable (mean 15.5 s; range 11–20 s). The response was a plantar flexion of the right foot. Besides ECG and EOG, surface EMG of nine striate muscles varying in relevance to response execution was recorded. In agreement with the hypothesis, heart rate, eye movements, and m. mylohyoideus EMG were decreased at the end of the FP. An increase in the EMG of the agonist m. soleus, antagonist m. tibialis anterior, m. peroneus longus, and m. trapezius was found during the FP. The activity in all other response-irrelevant muscles did not significantly differ from baseline. It was concluded that the results are at variance with the cardiac-somatic coupling hypothesis. Changes in surface EMG are discussed in terms of motor preparation.

Proving total dual integrality with cross-free families - a general framework

Abstract: We present a theorem stating that certain classes of linear programming problems have integer optimal (primal and dual) solutions. The theorem includes as special cases earlier results of Johnson, Edmonds and Giles, Frank, Hoffman and Schwartz, Groflin and Hoffman, and Lawler and Martel. The proof method consists of deriving total dual integrality for the corresponding system of linear inequalities from the total unimodularity of certain ‘cross-free’ subsystems. The scheme presented here differs from the one proposed earlier by Grishuhin in that Grishuhin requires the total unimodularity of cross-free subsystems in the axioms, whereas here this follows from easier verifiable axioms.

The power of weighted and ordinary least squares with estimated unequal variances in experimental design

Abstract: Response variances, var(yi), are estimated using replications for each experimental condition. The resulting estimated variances can be used to derive the correct variances of the Ordinary A 2 Least Squares (OLS) estimators β. The estimates si can also be used to compute the Estimated Weighted Least Squares (EWLS) estimators β* . The asymptotic covariance formula for EWLS might be utilized to test the EWLS estimators. The type I and type I1 errors of this test procedure are compared to the corresponding A errors for the OLS estimators β.

The influence of response side on the readiness potential prior to finger and foot movements. A preliminary report.

Abstract: Kornhuber and Deecke (1965) and Gilden et al. (1966) were the first to analyze cerebral activity recorded prior to voluntary movements. The readiness potential (RP) preceding a unilateral movement is present over both hemispheres from frontal to parietal areas. An abundance of R P literature concerns finger or hand movements. In their first papers, both Kornhuber and Deecke and Gilden et al. discussed foot movements as well and pointed to a similarity in shape of the RPs prior to finger movements and prior to foot movements. The scalp distribution of the R P preceding a foot movement was described by Vaughan et al. (1968). It was said to be compatible with the well known somatotopic organization of the motor cortex. In a recent experiment in which R P and the contingent negative variation (CNV) were recorded together, a slight tendency to larger R P amplitudes over the right hemisphere prior to a right foot movement was found (Brunia and Vingerhoets, 1981). This result was considered an argument in favor of a common generator of R P and CNV late wave, because the latter is also larger over the ipsilateral hemisphere prior to a plantar flexion of the right foot (Brunia, 1980a,b). Since the projection area of the calf muscles lies in the depth near the midline, it is quite possible that from this area field potentials are generated which are more easily picked up by electrodes over the opposite hemisphere. In order to get more evidence for this interpretation, it was decided to do an experiment in which RPs were investigated prior to finger and foot movements on either side. It was hypothesized that prior to finger movements larger contralateral amplitudes would be found and that prior to foot movements larger ipsilateral amplitudes would be found.

Spatial accuracy and programming of movement velocity

Abstract: Two experiments in which the effect of average movement velocity on reaction time is examined in relation to spatial accuracy are reported. Experiment 1 tested the hypothesis that fast inaccurate movements are more easily accessed during response selection by varying the compatibility of the stimulus-response relation. The second experiment employed spatially accurate movements in combination with the task variables S-R compatibility and foreperiod duration. The results are consistent with a two-stage motor-preparation notion consisting of a motor-programming stage and a program-loading stage.

Unemployment Insurance and Cyclical Growth

Abstract: As Goodwin’s famous model1) is built on a small set of rigorous assumptions it provides a large field for generalizations. Although quite a lot of different contributions have been made already, we have not seen any attempt to account, in its framework, for elements of the “welfare state” so far.2) From a theoretical point of view the incorporation into the model of unemployment benefits schemes seems to us highly relevant, because it allows to discuss the following questions: Will such schemes affect the cyclical characteristics of the model significantly or even abolish cyclical features? What difference will it make in which way those payments are financed and to which degree the burden of providing the necessary funds is divided between labour and capital? Will the payment of unemployment benefits affect the bargaining power of workers? What effects can be expected from attempts to “correct” the burden of contributions via wage negotiations? Can we allow for deficits and surplusses arising necessarily with certain assumptions about institutional rules? Although this list of questions is by no means complete, we cannot even fully work out the answers to them in the present article.

An eye movement analysis system (EMAS) for the identification of cognitive processes on figural tasks

Abstract: EMAS is a software system (written in VAX-11 FORTRAN) for the analysis of eye movement data recorded during the performance of figural tasks. Its main functions are: (1) Calibration of raw coordinates of eye movements to determine their actual position on the stimulus display. Different kinds of measurement distortion may be corrected. (2) Identification of eye fixations and the determination of their locations and durations. (3) Analysis of fixation sequences. The frequency of transitions of fixations among specified sectors of the stimulus display is computed. A sequential list is made of the successive fixations in which the fixated sector and the fixation duration are graphically indicated. (4) Plotting of raw or calibrated eye movement data and fixation points. The sequence of fixations in specified display sectors can also be plotted in real time. Applications of the programs to the Embedded Figures Test and the Hidden Figures Test are illustrated.

Melioration and maximization of reinforcement minus costs of behavior

Abstract: Eight pigeons were exposed to independent concurrent schedules. Concurrent variable-interval 60-second variable-interval 60-second schedules were presented to one group of four subjects. Following baseline training, a limited hold was added to one of the schedules and the duration of the hold was decreased in successive conditions. Concurrent variable-interval 120-second variable-interval 40-second schedules were presented to another group of four subjects. These subjects were first exposed to decreasing durations of a limited hold in the variable-interval 40-second component. After replication of the baseline, a limited hold in the variable-interval 120-second component was decreased in duration. The initial durations of the holds were determined from the subjects' responding in the baseline conditions. A duration was chosen such that approximately 25% of the scheduled reinforcers would be canceled if responding remained unchanged.Approximate matching of time proportions and reinforcement proportions was observed when the limited hold was added to the variable-interval 60-second schedule and when the limited hold was added to the variable-interval 40-second schedule. Time proportions were less extreme than reinforcement proportions when the limited hold operated in a variable-interval 120-second schedule. Overall reinforcement rates tended to decrease with continued training in concurrent schedules with a limited hold. Absolute deviations from time matching also decreased. The results provide evidence against the principle of reinforcement maximization, and support Herrnstein and Vaughan's (1980) melioration hypothesis.

Eye-Movement patterns in disabled readers at two age levels: A test of Bakker's balance model

Abstract: The eye-movement patterns of good and poor readers at two age levels during slide-presented reading, arithmetic and perceptual-closure tasks were compared. Older dyslexics were deficient in reading and arithmetic, but performed well on perceptual-closure tasks. Younger dyslexics were deficient on all tasks. Both younger good readers and older poor readers appeared to use a right-hemispheric reading strategy, while older dyslexics appeared to show a left-hemispheric approach. Younger dyslexics did not exhibit any strategy at all. Implications for Bakker's balance model of dyslexia and for subtypes research in dyslexia are discussed.

The resolution of quantificational ambiguity in the TENDUM system

Abstract: A method is described for handling the ambiguity and vagueness that is often found in quantifications - the semantically complex relations between nominal and verbal constituents. In natural language certain aspects of quantification are often left open; it is argued that the analysis of quantification in a model-theoretic framework should use semantic representation in which this may also be done. This paper shows a form for such a representation and how "ambiguous" representations are used in an elegant and efficient procedure for semantic analysis, incorporated in the TENDUM dialogue system.

The resolution of quantificational ambiguity in the tendum system

Abstract: A method is described for handling the ambiguity and vagueness that is often found in quantifications - the semantically complex relations between nominal and verbal constituents. In natural language certain aspects of quantification are often left open; it is argued that the analysis of quantification in a model-theoretic framework should use semantic representation in which this may also be done. This paper shows a form for such a representation and how "ambiguous" representations are used in an elegant and efficient procedure for semantic analysis, incorporated in the TENDUM dialogue system.

Policy solutions for a linked model for two common market countries

Abstract: Mini-Interplay consists of two linked macroeconometric policy models for the Federal Republic of Germany and the Netherlands. The policy evaluation problem is formulated as a linear quadratic difference game. Algorithms are given for stagewise solutions with a pure feedback information structure for three solution concepts: the “noncooperative” Nash, the “hierarchical” Stackelberg and the “cooperative” Pareto concept. The set of Pareto solutions is parametrized by the weighing factor of the two cost functionals. The preferences are chosen such that acceptable Nash and Stackelberg solutions result. It is tried to meet the target paths of the objective variables or to do better under the restriction that the use of instrumental variables stays within acceptable bounds. The mostly unrealistic symmetry of the quadratic cost-functionals is taken into account. Those end-costs of the Pareto solutions which are individually rational with respect to the end-costs of the Nash solution form possible outcomes of a bargaining game. Following the axiomatic approach Nash and Kalai-Smorodinsky arbitration schemes are applied to arrive at acceptable Pareto solutions. Unfortunately, the corresponding weighing factors are not invariant under equivalent cost-functional representations.