665 research outputs found

    Communicated beliefs about action-outcomes: The role of initial confirmation in the adoption and maintenance of unsupported beliefs

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    As agents seeking to learn how to successfully navigate their environments, humans can both obtain knowledge through direct experience, and second-hand through communicated beliefs. Questions remain concerning how communicated belief (or instruction) interacts with first-hand evidence integration, and how the former can bias the latter. Previous research has revealed that people are more inclined to seek out confirming evidence when they are motivated to uphold the belief, resulting in confirmation bias. The current research explores whether merely communicated beliefs affect evidence integration over time when it is not of interest to uphold the belief, and all evidence is readily available. In a novel series of on-line experiments, participants chose on each trial which of two options to play for money, being exposed to outcomes of both. Prior to this, they were exposed to favourable communicated beliefs regarding one of two options. Beliefs were either initially supported or undermined by subsequent probabilistic evidence (probabilities reversed halfway through the task, rendering the options equally profitable overall). Results showed that while communicated beliefs predicted initial choices, they only biased subsequent choices when supported by initial evidence in the first phase of the experiment. Findings were replicated across contexts, evidence sequence lengths, and probabilistic distributions. This suggests that merely communicated beliefs can prevail even when not supported by long run evidence, and in the absence of a motivation to uphold them. The implications of the interaction between communicated beliefs and initial evidence for areas including instruction effects, impression formation, and placebo effects are discussed

    Rewards enhance proactive and reactive control in adolescence and adulthood

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    Cognitive control allows the coordination of cognitive processes to achieve goals. Control may be sustained in anticipation of goal-relevant cues (proactive control) or transient in response to the cues themselves (reactive control). Adolescents typically exhibit a more reactive pattern than adults in the absence of incentives. We investigated how reward modulates cognitive control engagement in a letter array working memory (WM) task in 30 adolescents (12-17 years) and 20 adults (23-30 years) using a mixed block- and event-related functional magnetic resonance imaging design. After a Baseline run without rewards, participants performed a Reward run where 50% trials were monetarily rewarded. Accuracy and reaction time (RT) differences between Reward and Baseline runs indicated engagement of proactive control, which was associated with increased sustained activity in the bilateral anterior insula (AI), right dorsolateral prefrontal cortex (PFC) and right posterior parietal cortex (PPC). RT differences between Reward and No reward trials of the Reward run suggested additional reactive engagement of cognitive control, accompanied with transient activation in bilateral AI, lateral PFC, PPC, supplementary motor area, anterior cingulate cortex, putamen and caudate. Despite behavioural and neural differences during Baseline WM task performance, adolescents and adults showed similar modulations of proactive and reactive control by reward

    Thoughts About Actions and Outcomes: (And What They Lead to)

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    The idea that actions and their outcomes are mentally represented as associative knowledge structures has been influential in social psychology and motivation science. Among others, it suggests that thinking of, perceiving, or activating outcome representations in any other way can lead to the activation of associated action representations, triggering goal-directed action. In the current article, I critically examine the existing evidence for such ideomotor action. I argue that the evidence for ideomotor action obtained by the dominant paradigms in the field is open to alternative interpretations and present evidence suggesting that ideomotor action could also result from causal models about actions and outcomes rather than only from mere associations between their representations. I conclude that as a result, ideomotor action may be much more situated and flexible than previously thought, which has consequences for our thinking about goal-directed action

    Quantum criticality in the cubic heavy-fermion system CeIn_{3-x}Sn_x

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    We report a comprehensive study of CeIn3x_{3-x}Snx_x (0.55x0.8)(0.55 \leq x \leq 0.8) single crystals close to the antiferromagnetic (AF) quantum critical point (QCP) at xc0.67x_c\approx 0.67 by means of the low-temperature thermal expansion and Gr\"uneisen parameter. This system represents the first example for a {\it cubic} heavy fermion (HF) in which TNT_{\rm N} can be suppressed {\it continuously} down to T=0. A characteristic sign change of the Gr\"uneisen parameter between the AF and paramagnetic state indicates the accumulation of entropy close to the QCP. The observed quantum critical behavior is compatible with the predictions of the itinerant theory for three-dimensional critical spinfluctuations. This has important implications for the role of the dimensionality in HF QCPs.Comment: Physical Review Letters, to be publishe

    Dissymmetrical tunnelling in heavy fermion metals

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    A tunnelling conductivity between a heavy fermion metal and a simple metallic point is considered. We show that at low temperatures this conductivity can be noticeably dissymmetrical with respect to the change of voltage bias. The dissymmetry can be observed in experiments on the heavy fermion metals whose electronic system has undergone the fermion condensation quantum phase transition.Comment: 7 pages, Revte

    Magnetic-Field Induced Quantum Critical Point in YbRh2_2Si2_2

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    We report low-temperature calorimetric, magnetic and resistivity measurements on the antiferromagnetic (AF) heavy-fermion metal YbRh2_2Si2_2 (TN={T_N =} 70 mK) as a function of magnetic field BB. While for fields exceeding the critical value Bc0{B_{c0}} at which TN0{T_N\to0} the low temperature resistivity shows an AT2{AT^2} dependence, a 1/(BBc0){1/(B-B_{c0})} divergence of A(B){A(B)} upon reducing BB to Bc0{B_{c0}} suggests singular scattering at the whole Fermi surface and a divergence of the heavy quasiparticle mass. The observations are interpreted in terms of a new type of quantum critical point separating a weakly AF ordered from a weakly polarized heavy Landau-Fermi liquid state.Comment: accepted for publication in Phys. Rev. Let

    Field-induced quantum critical route to a Fermi liquid in high-temperature superconductors

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    In high transition temperature (T_c) superconductivity, charge doping is a natural tuning parameter that takes copper oxides from the antiferromagnet to the superconducting region. In the metallic state above T_c the standard Landau's Fermi-liquid theory of metals as typified by the temperature squared (T^2) dependence of resistivity appears to break down. Whether the origin of the non-Fermi-liquid behavior is related to physics specific to the cuprates is a fundamental question still under debate. We uncover a new transformation from the non-Fermi- to a standard Fermi-liquid state driven not by doping but by magnetic field in the overdoped high-T_c superconductor Tl_2Ba_2CuO_{6+x}. From the c-axis resistivity measured up to 45 T, we show that the Fermi-liquid features appear above a sufficiently high field which decreases linearly with temperature and lands at a quantum critical point near the superconductivity's upper critical field -- with the Fermi-liquid coefficient of the T^2 dependence showing a power-law diverging behavior on the approach to the critical point. This field-induced quantum criticality bears a striking resemblance to that in quasi-two dimensional heavy-Fermion superconductors, suggesting a common underlying spin-related physics in these superconductors with strong electron correlations.Comment: 6 pages, 4 figure
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