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Internal Representations of Temporal Statistics and Feedback Calibrate Motor-Sensory Interval Timing
Humans have been shown to adapt to the temporal statistics of timing tasks so as to optimize the accuracy of their responses, in agreement with the predictions of Bayesian integration. This suggests that they build an internal representation of both the experimentally imposed distribution of time intervals (the prior) and of the error (the loss function). The responses of a Bayesian ideal observer depend crucially on these internal representations, which have only been previously studied for simple distributions. To study the nature of these representations we asked subjects to reproduce time intervals drawn from underlying temporal distributions of varying complexity, from uniform to highly skewed or bimodal while also varying the error mapping that determined the performance feedback. Interval reproduction times were affected by both the distribution and feedback, in good agreement with a performance-optimizing Bayesian observer and actor model. Bayesian model comparison highlighted that subjects were integrating the provided feedback and represented the experimental distribution with a smoothed approximation. A nonparametric reconstruction of the subjective priors from the data shows that they are generally in agreement with the true distributions up to third-order moments, but with systematically heavier tails. In particular, higher-order statistical features (kurtosis, multimodality) seem much harder to acquire. Our findings suggest that humans have only minor constraints on learning lower-order statistical properties of unimodal (including peaked and skewed) distributions of time intervals under the guidance of corrective feedback, and that their behavior is well explained by Bayesian decision theory. 相似文献
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Sequence complexity and diversity of polyadenylated RNA molecules transcribed in human myeloid cells
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Alberto Buson Alessandro Negro Luigi Grassato Massimo Tagliaro Marina Basaglia Claudio Grandi Angelo Fontana Marco P. Nuti 《FEMS microbiology letters》1996,145(1):55-62
Abstract A clone positive for d-carbamoylase activity (2.7 kb Hin dIII- Bam H1 DNA fragment) was obtained by screening a genomic library of Agrobacterium radiobacter in Escherichia coli . This DNA fragment contains an open reading frame of 912 bp which is predicted to encode a peptide of 304 amino acids with a calculated molecular mass of 34247 Da. The d-carbamoylase gene. named cauA , was placed under the control of T7 RNA-dependent promoter and expressed in E. coli BL21 (DE3). After induction with isopropyl-thio-β-d-galactopyranoside, the synthesis of d-carbamoylase in E. coli reached about 40% of the total protein. The expressed protein was shown to possess a molecular mass, on SDS-PAGE, of 36 kDa and showed an enhanced allowed us to establish that a Pro14 →Leu14 exchange leads to an inactive enzyme species, while a Cys279 →Ser279 exchange did not impair the functional properties of the enxyme. 相似文献
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Summary Binding of azide to a series of copper(II) complexes has been investigated by absorption, CD and EPR spectroscopy. Axial binding of azide to Cu(II) can be differentiated from equatorial binding through the lower intensity and lack of optical activity of the LMCT band. The affinity of azide for Cu(II) increases with the overall positive charge of the complex. The preliminary data on thiocyanate binding to Cu(II) seem to agree with the trends observed for the corresponding azide adducts. 相似文献
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Summary Four derivatives ofCarcinus maenas hemocyanin containing Co(II) in the active site have been prepared under different experimental conditions. Two of them contain one Co(II) ion/active site and most probably represent isomeric forms containing Co(II) either in the fast-reacting or in the slow-reacting position within the active site. A third derivative contains two Co(II) ions active site, which reproduces the metal/protein stoichiometry of native hemocyanin. The fourth derivative is a metal hybrid form containing one Cu(I) ion and one Co(II) ion/active site. The derivatives have been characterized by absorption, circular dichroic and fluorescence spectroscopies. The results indicate that in all derivatives the metal is bound with a low coordination number, in agreement with the presence of three histidine residues/copper ion in the native protein. The two alternative metal-binding positions have different structures as shown by the different spectroscopic properties of the bound Co(II) ions. A marked hyperchromic effect on the optical absorption of Co(II) is observed as a result of the presence of a metal ion in the neighbouring metal-binding position in the active site. 相似文献
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Susanna Voltolini Giovanni Orengo Luigi Fontana Arsenio Corrado Negrini 《Aerobiologia》1992,8(3):349-354
Summary Fifty workers from two grain elevator terminals were examined to evaluate the prevalence of respiratory symptoms and their relationship with grain dust exposure.Fifty per cent of subjects complained of respiratory symptoms (rhinitis, asthma, chronic cough and dyspnea on exertion). In 34% of the workers the ventilatory function revealed some abnormalities (slight or moderate obstruction).Twenty-two (44%) showed a positive cutaneous reaction to one or more of the allergens tested, mostly towardsDermatophagoides and storage mites. The self-measurement of PEF over 14 days in 27 workers, showed significant differences between symptomatic and asymptomatic subjects. In particular, the results obtained from the cutaneous reactions could suggest a bronchial hypereactivity, worsened by the working exposure to dusts. The monitoring of PEF appears to be a simple and useful method for investigating the relationship between respiratory symptoms and the working environment. 相似文献