124 research outputs found
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The effects of learning Logo on the ability of concrete operational students to learn abstract concepts.
Overzicht, flexibiliteit en aanpassingsvermogen: De kracht van de bestuurskundige als adviseur
Hoe werkt bestuurskunde?
Bestuurskunde studeren en dan… een baan. Hoe gaat dat of liever gezegd hoe werkt bestuurskunde in de praktijk
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Choice behavior as a function of memory in preschool children
The purpose of this study was to investigate the memory factors
associated with preschoolers' performance in a two-choice, uncertain
outcome decision situation. Choice behavior was examined under
two conditions: one, (NMA), in which the child was required to
rely on his memory to establish an appropriate prediction of the
occurrence of two events; and one (MA), in which the child was provided
with a visual record of events as they actually occurred, which
he might scan in order to establish an appropriate prediction. Five
major hypotheses were tested:
1. Childrens stable-state strategies will not differ in the
MA vs. the NMA condition for either sex.
2. Children of both sexes will make a smaller proportion of
errors in arriving at a stable-state strategy in the
memory aid condition vs. the non-memory aid condition.
3. Children of both sexes will stabilize earlier in the series
in the memory aid condition vs. those in the non-memory
aid condition.
4. The proportion of children who stabilize at a level higher
than the common median for the two event distributions
will be larger in the 75:25 event condition than in the 65:35
event condition; the proportion will not differ for boys and
girls, but will be significantly greater than the proportion
expected by chance.
5. There is no difference in the predicted and observed
stable-state strategies of subjects for either sex within
memory conditions.
The sample used for the comparison consisted of 39 middle-class preschool children chosen on the basis of availability. Subjects
were randomly assigned to all experimental conditions in an
effort to control for bias due to individual differences, practice, and
order effects.
The apparatus was a pegboard with 106 holes. The two events
were defined by the position of a peg in the board, an "up" position
or a "down" position. The occurrence of the two events was determined
by one of eight random schedules. The subjects served as
their own controls across the memory conditions.
The data for the first, third, fourth and fifth hypotheses were in the form of p values, the proportion in which the subject chose
the most frequently occurring event. The data for the second hypothesis
were subjects' errors in choices of the events as they actually
occurred in the first 80 "learning" trials.
The first hypothesis, which predicted that subjects would perform
at a higher level when provided with a memory aid, was not
tenable as the data were found to support the alternative hypothesis
that subjects without the memory aid exhibited a more adequate performance.
Girls performing without the memory aid exhibited a
higher stable-state performance than when they were provided with a
memory aid. For boys, stable-state behavior in the two memory
conditions did not differ.
The test of the second hypothesis, which pertained to accuracy
of performance, showed that proportion of errors across the first
80 trials was similar for both sexes, whether or not a memory aid
was provided.
The third hypothesis, regarding rate of learning, was untestable
since none of the experimental groups stabilized. The learning
curves generated from the median data indicated that learning did
occur in the early part of the task and that in the final block of trials,
performance deteriorated in the memory aid condition and improved
in the non-memory aid condition in relation to the level achieved
midway through the task.
Results from the test of hypothesis four, used to determine
whether or not children employed probability rules in selecting the
more frequent event in the stable-state, indicate that subjects did
not change in performance in the 75:25 event distribution in relation
to their performance in the 65:35 event distribution. This was the
case whether or not a memory-aid was provided. In fact, only
three of the experimental groups performed at a level better than
chance, all of which were performances in the non-memory aid condition;
all memory aid performances plus the performance of the
boys in the non-memory aid 75:25 event distribution failed to exceed
chance performance.
The quantitative test of the Siegel mathematical model of
choice behavior, provided through hypothesis five, indicated that the
model's predictions of stable-state strategies did not differ significantly
from the observed stable-state strategies for any of the
groups in either memory condition. That is, the Siegel model allowed
for quantitatively accurate predictions of stable-state choice
behavior of both sexes in this preschool sample, whether or not a
memory aid was provided.
The discrepancy in performance found in favor of the non-memory aid condition was tentatively explained in terms of the inability
of preschoolers to use the complex information made available
through the memory aid and in terms of the concept of utility of variability. The fact that only three quarters of the subjects performed
at a better than chance level (and these only in the non-memory aid condition) severely limited the information yielded by
the study and the comparisons that could be made with other studies.
In general, the results are consistent with the findings of Weir's
1967 study in which a memory aid was used in conjunction with reinforcement.
The study points up the need for further investigation
of memory factors as they relate to probability learning, asymptotic
performance and an adequate memory aid, with regard to choice
behavior of preschool children
Grading of Frequency Spectral Centroid Across Resting-State Networks
Ongoing, slowly fluctuating brain activity is organized in resting-state networks (RSNs) of spatially coherent fluctuations. Beyond spatial coherence, RSN activity is governed in a frequency-specific manner. The more detailed architecture of frequency spectra across RSNs is, however, poorly understood. Here we propose a novel measure–the Spectral Centroid (SC)–which represents the center of gravity of the full power spectrum of RSN signal fluctuations. We examine whether spectral underpinnings of network fluctuations are distinct across RSNs. We hypothesize that spectral content differs across networks in a consistent way, thus, the aggregate representation–SC–systematically differs across RSNs. We therefore test for a significant grading (i.e., ordering) of SC across RSNs in healthy subjects. Moreover, we hypothesize that such grading is biologically significant by demonstrating its RSN-specific change through brain disease, namely major depressive disorder. Our results yield a highly organized grading of SC across RSNs in 820 healthy subjects. This ordering was largely replicated in an independent dataset of 25 healthy subjects, pointing toward the validity and consistency of found SC grading across RSNs. Furthermore, we demonstrated the biological relevance of SC grading, as the SC of the salience network–a RSN well known to be implicated in depression–was specifically increased in patients compared to healthy controls. In summary, results provide evidence for a distinct grading of spectra across RSNs, which is sensitive to major depression
Ongoing Slow Fluctuations in V1 Impact on Visual Perception
The human brain's ongoing activity is characterized by intrinsic networks of coherent fluctuations, measured for example with correlated functional magnetic resonance imaging signals. So far, however, the brain processes underlying this ongoing blood oxygenation level dependent (BOLD) signal orchestration and their direct relevance for human behavior are not sufficiently understood. In this study, we address the question of whether and how ongoing BOLD activity within intrinsic occipital networks impacts on conscious visual perception. To this end, backwardly masked targets were presented in participants' left visual field only, leaving the ipsi-lateral occipital areas entirely free from direct effects of task throughout the experiment. Signal time courses of ipsi-lateral BOLD fluctuations in visual areas V1 and V2 were then used as proxies for the ongoing contra-lateral BOLD activity within the bilateral networks. Magnitude and phase of these fluctuations were compared in trials with and without conscious visual perception, operationalized by means of subjective confidence ratings. Our results show that ipsilateral BOLD magnitudes in V1 were significantly higher at times of peak response when the target was perceived consciously. A significant difference between conscious and non-conscious perception with regard to the pre-target phase of an intrinsic-frequency regime suggests that ongoing V1 fluctuations exert a decisive impact on the access to consciousness already before stimulation. Both effects were absent in V2. These results thus support the notion that ongoing slow BOLD activity within intrinsic networks covering V1 represents localized processes that modulate the degree of readiness for the emergence of visual consciousness
Frequency-Dependent Spatial Distribution of Functional Hubs in the Human Brain and Alterations in Major Depressive Disorder
Alterations in large-scale brain intrinsic functional connectivity (FC), i.e., coherence between fluctuations of ongoing activity, have been implicated in major depressive disorder (MDD). Yet, little is known about the frequency-dependent alterations of FC in MDD. We calculated frequency specific degree centrality (DC) – a measure of overall FC of a brain region – within 10 distinct frequency sub-bands accessible from the full range of resting-state fMRI BOLD fluctuations (i.e., 0.01–0.25 Hz) in 24 healthy controls and 24 MDD patients. In healthy controls, results reveal a frequency-specific spatial distribution of highly connected brain regions – i.e., hubs – which play a fundamental role in information integration in the brain. MDD patients exhibited significant deviations from the healthy DC patterns, with decreased overall connectedness of widespread regions, in a frequency-specific manner. Decreased DC in MDD patients was observed predominantly in the occipital cortex at low frequencies (0.01–0.1 Hz), in the middle cingulate cortex, sensorimotor cortex, lateral parietal cortex, and the precuneus at middle frequencies (0.1–0.175 Hz), and in the anterior cingulate cortex at high frequencies (0.175–0.25 Hz). Additionally, decreased DC of distinct parts of the insula was observed across low, middle, and high frequency bands. Frequency-specific alterations in the DC of the temporal, insular, and lateral parietal cortices correlated with symptom severity. Importantly, our results indicate that frequency-resolved analysis within the full range of frequencies accessible from the BOLD signal – also including higher frequencies (>0.1 Hz) – reveals unique information about brain organization and its changes, which can otherwise be overlooked
The heat kernel of the compactified D=11 supermembrane with non-trivial winding
We study the quantization of the regularized hamiltonian, , of the
compactified D=11 supermembrane with non-trivial winding. By showing that
is a relatively small perturbation of the bosonic hamiltonian, we construct a
Dyson series for the heat kernel of and prove its convergence in the
topology of the von Neumann-Schatten classes so that is ensured to be
of finite trace. The results provided have a natural interpretation in terms of
the quantum mechanical model associated to regularizations of compactified
supermembranes. In this direction, we discuss the validity of the Feynman path
integral description of the heat kernel for D=11 supermembranes and obtain a
matrix Feynman-Kac formula.Comment: 19 pages. AMS LaTeX. A whole new section was added and some other
minor changes in style where mad
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