Testing learning mechanisms of rule-based judgment

Weighing the importance of different pieces of information is a key determinant of making accurate judgments. In social judgment theory, these weighting processes have been successfully described with linear models. How people learn to make judgments has received less attention. Although the hitherto proposed delta learning rule can perfectly learn to solve linear problems, reanalyzing a previous experiment showed that it does not adequately describe human learning. To provide a more accurate description of learning processes we amended the delta learning rule with three learning mechanisms—a decay, an attentional learning mechanism, and a capacity limitation. An additional study tested the different learning mechanisms in predicting learning in linear judgment tasks. In this study, participants first learned to predict a continuous criterion based on four cues. To test the three learning mechanisms rigorously against each other, we changed the importance of the cues after 200 trials so that the mechanisms make different predictions with regard to how fast people adapt to the new environment. On average, judgment accuracy improved from Trial 1 to Trial 200, dropped when the task environment changed, but improved again until the end of the task. The capacity-restricted learning model, restricting how much people update the cue weights on a single trial, best described and predicted the learning curve of the majority of participants. Taken together, these results suggest that considering cognitive constraints within learning models may help to understand how humans learn when making inferences

Pillars of Judgment:How Memory Abilities Affect Performance in Rule-Based and Exemplar-Based Judgments

Making accurate judgments is an essential skill in everyday life. Although how different memory abilities relate to categorization and judgment processes has been hotly debated, the question is far from resolved. We contribute to the solution by investigating how individual differences in memory abilities affect judgment performance in 2 tasks that induced rule-based or exemplar-based judgment strategies. In a study with 279 participants, we investigated how working memory and episodic memory affect judgment accuracy and strategy use. As predicted, participants switched strategies between tasks. Furthermore, structural equation modeling showed that the ability to solve rule-based tasks was predicted by working memory, whereas episodic memory predicted judgment accuracy in the exemplar-based task. Last, the probability of choosing an exemplar-based strategy was related to better episodic memory, but strategy selection was unrelated to working memory capacity. In sum, our results suggest that different memory abilities are essential for successfully adopting different judgment strategies

Tracing the path of forgetting in rule abstraction and exemplar retrieval

People often forget acquired knowledge over time such as names of former classmates. Which knowledge people can access, however, may modify the judgement process and affect judgement accuracy. Specifically, we hypothesised that judgements based on retrieving past exemplars from long-term memory may be more vulnerable to forgetting than remembering rules that relate the cues to the criterion. Experiment 1 systematically tracked the individual course of forgetting from initial learning to later tests (immediate, 1 day, and 1 week) in a linear judgement task facilitating rule-based strategies and a multiplicative judgement task facilitating exemplar-based strategies. Practising the acquired judgement strategy in repeated tests helped participants to consistently apply the learnt judgement strategy and retain a high judgement accuracy even after a week. Yet, whereas a long retention interval did not affect judgements in the linear task, a long retention interval impaired judgements in the multiplicative task. If practice was restricted as in Experiment 2, judgement accuracy suffered in both tasks. In addition, after a week without practice, participants tried to reconstruct their judgements by applying rules in the multiplicative task. These results emphasise that the extent to which decision makers can still retrieve previously learned knowledge limits their ability to make accurate judgements and that the preferred strategies change over time if the opportunity for practice is limited

Correlations in STAR: interferometry and event structure

STAR observes a complex picture of RHIC collisions where correlation effects of different origins -- initial state geometry, semi-hard scattering, hadronization, as well as final state interactions such as quantum intensity interference -- coexist. Presenting the measurements of flow, mini-jet deformation, modified hadronization, and the Hanbury Brown and Twiss effect, we trace the history of the system from the initial to the final state. The resulting picture is discussed in the context of identifying the relevant degrees of freedom and the likely equilibration mechanism.Comment: 8 pages, 6 figures, plenary talk at the 5th International Conference on Physics and Astrophysics of Quark Gluon Plasma, to appear in Journal of Physics G (http://www.iop.org

Strangelet search at RHIC

Two position sensitive Shower Maximum Detector (SMDs) for Zero-Degree Calorimeters (ZDCs) were installed by STAR before run 2004 at both upstream and downstream from the interaction point along the beam axis where particles with small rigidity are swept away by strong magnetic field. The ZDC-SMDs provides information about neutral energy deposition as a function of transverse position in ZDCs. We report the preliminary results of strangelet search from a triggered data-set sampling 100 million Au+Au collisions at top RHIC energy.Comment: Strange Quark Matter 2004 conference proceedin

Azimuthal anisotropy and correlations at large transverse momenta in p+p and Au+Au collisions at sqrt[sNN] = 200 GeV

Results on high transverse momentum charged particle emission with respect to the reaction plane are presented for Au+Au collisions at sqrt[sNN]=200 GeV. Two- and four-particle correlations results are presented as well as a comparison of azimuthal correlations in Au+Au collisions to those in p+p at the same energy. The elliptic anisotropy v2 is found to reach its maximum at pt~3 GeV/c, then decrease slowly and remain significant up to pt ~ 7-10 GeV/c. Stronger suppression is found in the back-to-back high-pt particle correlations for particles emitted out of plane compared to those emitted in plane. The centrality dependence of v2 at intermediate pt is compared to simple models based on jet quenching

Neutral Kaon Interferometry in Au+Au collisions at sqrt(s_NN) = 200 GeV

We present the first statistically meaningful results from two-K0s interferometry in heavy-ion collisions. A model that takes the effect of the strong interaction into account has been used to fit the measured correlation function. The effects of single and coupled channel were explored. At the mean transverse mass m_T = 1.07 GeV, we obtain the values R = 4.09 +/- 0.46 (stat.) +/- 0.31 (sys) fm and lambda = 0.92 +/- 0.23 (stat) +/- 0.13 (sys), where R and lambda are the invariant radius and chaoticity parameters respectively. The results are qualitatively consistent with m_T systematics established with pions in a scenario characterized by a strong collective flow.Comment: 11 pages, 10 figure

The Cytotoxic Necrotizing Factor of Yersinia pseudotuberculosis (CNFy) is Carried on Extracellular Membrane Vesicles to Host Cells

In this study we show Yersinia pseudotuberculosis secretes membrane vesicles (MVs) that contain different proteins and virulence factors depending on the strain. Although MVs from Y. pseudotuberculosis YPIII and ATCC 29833 had many proteins in common (68.8% of all the proteins identified), those located in the outer membrane fraction differed significantly. For instance, the MVs from Y. pseudotuberculosis YPIII harbored numerous Yersinia outer proteins (Yops) while they were absent in the ATCC 29833 MVs. Another virulence factor found solely in the YPIII MVs was the cytotoxic necrotizing factor (CNFy), a toxin that leads to multinucleation of host cells. The ability of YPIII MVs to transport this toxin and its activity to host cells was verified using HeLa cells, which responded in a dose-dependent manner; nearly 70% of the culture was multinucleated after addition of 5 mu g/ml of the purified YPIII MVs. In contrast, less than 10% were multinucleated when the ATCC 29833 MVs were added. Semi-quantification of CNFy within the YPIII MVs found this toxin is present at concentrations of 5 -10 ng per mu g of total MV protein, a concentration that accounts for the cellular responses see