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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, $H$, of the compactified D=11 supermembrane with non-trivial winding. By showing that $H$ is a relatively small perturbation of the bosonic hamiltonian, we construct a Dyson series for the heat kernel of $H$ and prove its convergence in the topology of the von Neumann-Schatten classes so that $e^{-Ht}$ 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