The neural bases of distracter-resistant working memory

A major difference between humans and other animals is our capacity to maintain information in working memory (WM) while performing secondary tasks, which enables sustained, complex cognition. A common assumption is that the lateral prefrontal cortex (PFC) is critical for WM performance in the presence of distracters, but direct evidence is scarce. We assessed the relationship between fMRI activity and WM performance within-subjects, with performance matched across Distracter and No-distracter conditions. Activity in ventrolateral PFC during WM encoding and maintenance positively predicted performance in both conditions, whereas activity in the pre-supplementary motor area (pre-SMA) predicted performance only under distraction. Other parts of dorsolateral and ventrolateral PFC predicted performance only in the No-distracter condition. These findings challenge a lateral PFC-centered view of distracter-resistance, and suggest that the lateral PFC supports a type of WM representation that is efficient for dealing with task-irrelevant input but is nonetheless easily disrupted by dual-task demands

Flavor-SU(3) tests from D0→K0K−π+D^0 \to K^0 K^- \pi^+ and D0→Kˉ0K+π−D^0 \to \bar K^0 K^+ \pi^- Dalitz plots

The processes $D^0\to K^0 K^-\pi^+$ and D^0\to\ok K^+\pi^- involve intermediate vector resonances whose amplitudes and phases are related to each other via flavor-SU(3) symmetry. Dalitz plots for these two processes can shed light on the usefulness of this symmetry in studying charm decays. Until this year the only available data on this process came from a conference report in 2002 by the BaBar Collaboration, but now an independent data sample of higher statistics has become available from the CLEO Collaboration. The goal is to predict Dalitz plot amplitudes and phases assuming flavor-SU(3) symmetry and compare them with experiment. An SU(3) fit can account for the relative magnitudes of the amplitudes for the decays $D^0 \to K^{*-}K^+$ and $D^0 \to K^{*+}K^-$, but neither the current BaBar sample (based on an integrated luminosity of 22 fb$^{-1}$) nor the CLEO analysis has significant evidence for the decays D^0\to K^{*0}\ok and D^0 \to \oks K^0. At this level one is unable to compare magnitudes and phases with theoretical predictions. The purpose of this Letter is to advocate an analysis using the full BaBar sample (more than 20 times the 2002 value). It should definitively determine whether predicted magnitudes and phases agree with experiment. A similar analysis should be possible with an even larger sample of events collected by the Belle Collaboration at KEK-B.Comment: 6 pages, 1 figure. As published in Physics Letters B. arXiv admin note: substantial text overlap with arXiv:1104.496

Bad Company: Reconciling Negative Peer Effects in College Achievement

Existing peer effects studies produce contradictory findings, including positive, negative, large, and small effects, despite similar contexts. We reconcile these results using U.S. Naval Academy data covering a 22-year history of the random assignment of students to peer groups. Coupled with students' limited discretion over freshman-year courses, our setting affords an opportunity to better understand peer effects in different social networks. We find negative effects at the broader "company" level (students' social and residential group) and positive effects at the narrower course-company level. We suggest that peer spillovers change direction because of differences in the underlying mechanism of peer influence

Bad Company: Reconciling Negative Peer Effects in College Achievement

Existing peer effects studies produce contradictory findings, including positive, negative, large, and small effects, despite similar contexts. We reconcile these results using U.S. Naval Academy data covering a 22-year history of the random assignment of students to peer groups. Coupled with students' limited discretion over freshman-year courses, our setting affords an opportunity to better understand peer effects in different social networks. We find negative effects at the broader "company" level (students' social and residential group) and positive effects at the narrower course-company level. We suggest that peer spillovers change direction because of differences in the underlying mechanism of peer influence

EGF Cell Surface Receptor Quantitaiion on Ocular Cells by an Immunocytochemical Flow Cyfometry Technique

A method is presented for the rapid flow cytometric determination of epidermal growth factor (EGF) receptor densities on the surface of cultured ocular cells. The technique uses a biotinylated monoclonal antibody directed against the EGF receptor in conjunction with a streptavidin-bound fluorochrome and requires the specific fluorescence per cell to be measured as a function of ligand and receptor concentration. Because the measurement is noninvasive and restricted to cell surface-bound material, the cells can be kept in a physiologic environment, even at the moment of assay. Calculated receptor densities ranged from 5142/cell (infant human corneal endothelium) to 35,678/cell (infant human keratocytes) to >5 X 10 5 /cell for an A431 control cell line. Species and donor age differences were noted, as was transient receptor downregulation after EGF administration. Flow cytometry represents a valuable time saving procedure for large scale applications while providing the same level of sensitivity as standard radioimmunoassays. This technique is applicable to quantitation of other growth factor cell surface receptors and could greatly expand the use of flow cytometry in the research laboratory. Inves

Studies of the decays D^0 \rightarrow K_S^0K^-\pi^+ and D^0 \rightarrow K_S^0K^+\pi^-

The first measurements of the coherence factor R_{K_S^0K\pi} and the average strong--phase difference \delta^{K_S^0K\pi} in D^0 \to K_S^0 K^\mp\pi^\pm decays are reported. These parameters can be used to improve the determination of the unitary triangle angle \gamma\ in B^- \rightarrow $\widetilde{D}K^-$ decays, where $\widetilde{D}$ is either a D^0 or a D^0-bar meson decaying to the same final state, and also in studies of charm mixing. The measurements of the coherence factor and strong-phase difference are made using quantum-correlated, fully-reconstructed D^0D^0-bar pairs produced in e^+e^- collisions at the \psi(3770) resonance. The measured values are R_{K_S^0K\pi} = 0.70 \pm 0.08 and \delta^{K_S^0K\pi} = (0.1 \pm 15.7)$^\circ$ for an unrestricted kinematic region and R_{K*K} = 0.94 \pm 0.12 and \delta^{K*K} = (-16.6 \pm 18.4)$^\circ$ for a region where the combined K_S^0 \pi^\pm invariant mass is within 100 MeV/c^2 of the K^{*}(892)^\pm mass. These results indicate a significant level of coherence in the decay. In addition, isobar models are presented for the two decays, which show the dominance of the K^*(892)^\pm resonance. The branching ratio {B}(D^0 \rightarrow K_S^0K^+\pi^-)/{B}(D^0 \rightarrow K_S^0K^-\pi^+) is determined to be 0.592 \pm 0.044 (stat.) \pm 0.018 (syst.), which is more precise than previous measurements.Comment: 38 pages. Version 3 updated to include the erratum information. Errors corrected in Eqs (25), (26), 28). Fit results updated accordingly, and external inputs updated to latest best known values. Typo corrected in Eq(3)- no other consequence