9,994 research outputs found
Learning to become an expert : reinforcement learning and the acquisition of perceptual expertise
To elucidate the neural mechanisms underlying the development of perceptual expertise, we recorded ERPs while participants performed a categorization task. We found that as participants learned to discriminate computer-generated "blob'' stimuli, feedback modulated the amplitude of the errorrelated negativity (ERN)-an ERP component thought to reflect error evaluation within medial-frontal cortex. As participants improved at the categorization task, we also observed an increase in amplitude of an ERP component associated with object recognition (the N250). The increase in N250 amplitude preceded an increase in amplitude of an ERN component associated with internal error evaluation (the response ERN). Importantly, these electroencephalographic changes were not observed for participants who failed to improve on the categorization task. Our results suggest that the acquisition of perceptual expertise relies on interactions between the posterior perceptual system and the reinforcement learning system involving medial-frontal cortex
Effects of exercise modalities on arterial stiffness and wave reflection: a systematic review and meta-analysis of randomized controlled trials
Background and Objectives:
Physical activity is associated with lower cardiovascular and all-cause mortality. However, the effects of different exercise modalities on arterial stiffness are currently unclear. Our objectives were to investigate the effects of exercise modalities (aerobic, resistance or combined) on pulse wave velocity (PWV) and augmentation index (AIx), and to determine whether the effects on these indices differed according to the participants' or exercise characteristics.
Methods:
We searched the Medline, Embase and Cochrane Library databases from inception until April 2014 for randomized controlled trials lasting ≥4 weeks investigating the effects of exercise modalities on PWV and AIx in adults aged ≥18 years.
Results:
Forty-two studies (1627 participants) were included in this analysis. Aerobic exercise improved both PWV (WMD: −0.63 m/s, 95% CI: −0.90, −0.35) and AIx (WMD:−2.63%, 95% CI: −5.25 to −0.02) significantly. Aerobic exercise training showed significantly greater reduction in brachial-ankle (WMD: −1.01 m/s, 95% CI: −1.57, −0.44) than in carotid-femoral (WMD: -0.39 m/s, 95% CI: −0.52, −0.27) PWV. Higher aerobic exercise intensity was associated with larger reductions in AIx (β: −1.55%, CI −3.09, 0.0001). In addition, aerobic exercise had a significantly larger effect in reducing PWV (WMD:−1.0 m/s, 95% CI: −1.43, −0.57) in participants with stiffer arteries (PWV ≥8 m/s). Resistance exercise had no effect on PWV and AIx. There was no significant effect of combined exercise on PWV and AIx.
Conclusions:
We conclude that aerobic exercise improved arterial stiffness significantly and that the effect was enhanced with higher aerobic exercise intensity and in participants with greater arterial stiffness at baseline.
Trial Registration PROSPERO:
Database registration: CRD42014009744,
The inner kiloparsec of the jet in 3C264
We present new multi-frequency EVN, MERLIN and VLA observations of the radio
source 3C264, sensitive to linear scales ranging from the parsec to several
kiloparsecs. The observations confirm the existence of regions with different
properties in the first kiloparsec of the jet. The most remarkable feature is
the transition between a well collimated narrow jet at distances from the core
below 80 pc, to a conical-shaped wide jet, with an opening angle of 20 degrees.
Another change of properties, consisting of an apparent deflection of the jet
ridge line and a diminution of the surface brightness, occurs at a distance of
300 pc from the core, coincident with the radius of a ring observed at optical
wavelengths. Our observations add new pieces of information on the spectrum of
the radio-optical jet of 3C264, with results consistent with a synchrotron
emission mechanism and a spectrum break frequency in the infrared. Brightness
profiles taken perpendicularly to the jet of 3C264 are consistent with a spine
brightened jet at distances below 100 pc from the core, and an edge-brightened
jet beyond, which can be interpreted as evidence of a transverse jet velocity
structure. Our observations do not allow us to distinguish between the presence
of a face--on dust and gas disk at the center of the host galaxy of 3C264, or
rather an evacuated bubble. However, the properties of the jet structure, the
changes in the polarization angle, and the plausible jet orientation can be
naturally brought into agreement in the bubble scenario.Comment: 10 pages, 9 figures, accepted in A&
Feeling Good about Giving: The Benefits (and Costs) of Self-Interested Charitable Behavior
In knowledge-intensive settings such as product or software development, fluid teams of individuals with different sets of experience are tasked with projects that are critical to the success of their organizations. Although building teams from individuals with diverse prior experience is increasingly necessary, prior work examining the relationship between experience and performance fails to find a consistent effect of diversity in experience on performance. The problem is that diversity in experience improves a team's information processing capacity and knowledge base, but also creates coordination challenges. We hypothesize that team familiarity - team members' prior experience working with one another - is one mechanism that helps teams leverage the benefits of diversity in team member experience by alleviating coordination problems that diversity creates. We use detailed project- and individual-level data from an Indian software services firm to examine the effects of team familiarity and diversity in experience on performance for software development projects. We find the interaction of team familiarity and diversity in experience has a complementary effect on a project being delivered on time and on budget. In team familiarity, we identify one mechanism for capturing the performance benefits of diversity in experience and provide insight into how the management of experience accumulation affects team performance.Diversity, Experience, Knowledge, Software, Team Familiarity
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