Does Hypothesis-Instruction Improve Learning?

Dual space models of problem solving (e.g., Simon & Lea, 1974; Klahr & Dunbar, 1988) assume that the problem space for a task consists of two spaces: an hypothesis space and an experiment space. In hypothesis space, hypotheses about rules governing the task are generated, which can then be tested in experiment space. However, experiment space can be searched by applying the operators even without knowledge about the task. W e predicted that people searching hypothesis space would learn more about the task. To test this claim, two experiments were performed in which subjects had to learn to control a system consisting of three input variables that had unknown links to three output variables. Subjects first explored the task, then they had to reach goal states for the output variables. In both experiments subjects were presented with an hypothesis about one of the links, which should foster search of hypothesis space. In Experiment 1, hypothesis instruction improved performance and we showed that it had a similar effect to a manipulation of goal specificity, suggesting that both factors improve learning by encouraging search in hypothesis space. In Experiment 2 subjects were given a correct hypothesis or an incorrect hypothesis. Both groups performed better than an appropriate control. Thus instructions that encourage hypothesis testing appear to improve learning in problem solving

Rewarding Multitasking: Negative Effects of an Incentive on Problem Solving under Divided Attention

Research has consistently shown negative effects of multitasking on tasks such as problem solving. This study was designed to investigate the impact of an incentive when solving problems in a multitasking situation. Incentives have generally been shown to increase problem solving (e.g., Wieth and Burns, 2006), however, it is unclear whether an incentive can increase problem solving while attentional resources are divided. Participants were either given an incentive or not and asked to complete incremental and insight problems while either in a dual-task or single task condition. After solving the problems participants were given a surprise memory test. Results showed that the incentive only led to increases in problem solving in the single task condition but not the dual-task condition. Furthermore, results showed that an incentive in the dual-task condition led to an increase in recall of irrelevant information. These findings indicate that an incentive cannot ameliorate the detrimental effects of multitasking when problem solving and may even lead to an increase in irrelevant information processing

Goals, Strategies, and Motivation

Goal-specificity has been found to affect performance: In difficult tasks, specific goals may be detrimental for learning. Locke and Latham (1990) claimed that goal-specificity has an impact on performance via motivation. Vollmeyer and Rheinberg's (1998) cognitive-motivational process model proposed that cognitive and motivational processes interact. Therefore, we investigated if goal-specificity may change the nature of this interaction, by trying to fit different structural equations models for groups given a specific goal (SG) or a nonspecific goal (NSG). Before beginning a complex dynamic task, the SG group was given a specific goal to reach, but the NSG group only received a goal when they had to transfer their knowledge. We found that the SG group learnt less and had lower motivation during learning. Contrary to earlier claims, there was no direct effect of goal-specificity on initial motivation, but it did alter the interaction between strategies and motivation during learning. The empirical model for the SG group showed a strong effect of initial motivation on the learning process and goal-directed strategies were effective. For the NSG group motivation during the task and systematic strategies were important

Goal Speciflcity in Hypothesis Testing and Problem Solving

Theories of skill acquisition have made radically different predictions about the role of means-ends analysis in acquiring general rules that promote effective transfer to new problems. Under one view, means-ends analysis is assumed to provide the basis for efficient knowledge compilation (Anderson, 1987), whereas under the alternative view means-ends analysis is believed to disrupt rule induction (Sweller, 1988). We suggest that in the absence of a specific goal people are more likely to use a rule-induction learning strategy, whereas providing a speciflc goal fosters use of means ends analysis, which is a non-rule-induction strategy. We performed an experiment to investigate the impact of goal specificity and systematicity of rule-induction strategies in learning and transfer within a complex dynamic system. Subjects who were provided with a specific goal were able to solve the initial problem, but were impaired on a transfer test using a similar problem with a different goal, relative to subjects who were encouraged to use a systematic rule-induction strategy to freely explore the problem space. Our results support Sweller's proposal that means-ends analysis leads to specific knowledge of an isolated solution path, but docs not provide an effective method for learning the overall structure of a problem space

Disorder and relaxation mode in the lattice dynamics of PbMg1/3_{1/3}Nb2/3_{2/3}O3_3 relaxor ferroelectric

The low-energy part of vibration spectrum in PbMg$_{1/3}$Nb$_{2/3}$O$_3$ relaxor ferroelectric was studied by inelastic neutron scattering. We observed the coexistence of a resolution-limited central peak with strong quasielastic scattering. The line-width of the quasielastic component follows a $\Gamma_0+Dq^2$ dependence. We find that $\Gamma_0$ is temperature-dependent. The relaxation time follows the Arrhenius law well. The presence of a relaxation mode associated with quasi-elastic scattering in PMN indicates that order-disorder behaviour plays an important r\^ole in the dynamics of diffuse phase transitions

Predictors of rapid aortic root dilation and referral for aortic surgery in Marfan syndrome

Few data exist regarding predictors of rapid aortic root dilation and referral for aortic surgery in Marfan syndrome (MFS). To identify independent predictors of the rate of aortic root (AoR) dilation and referral for aortic surgery, we investigated the data from the Pediatric Heart Network randomized trial of atenolol versus losartan in young patients with MFS. Data were analyzed from the echocardiograms at 0, 12, 24, and 36months read in the core laboratory of 608 trial subjects, aged 6months to 25 years, who met original Ghent criteria and had an AoR z-score (AoRz)>3. Repeated measures linear and logistic regressions were used to determine multivariable predictors of AoR dilation. Receiver operator characteristic curves were used to determine cut-points in AoR dilation predicting referral for aortic surgery. Multivariable analysis showed rapid AoR dilation as defined by change in AoRz/year>90th percentile was associated with older age, higher sinotubular junction z-score, and atenolol use (R-2=0.01) or by change in AoR diameter (AoRd)/year>90th percentile with higher sinotubular junction z-score and non-white race (R-2=0.02). Referral for aortic root surgery was associated with higher AoRd, higher ascending aorta z-score, and higher sinotubular junction diameter:ascending aorta diameter ratio (R-2=0.17). Change in AoRz of 0.72 SD units/year had 42% sensitivity and 92% specificity and change in AoRd of 0.34cm/year had 38% sensitivity and 95% specificity for predicting referral for aortic surgery. In this cohort of young patients with MFS, no new robust predictors of rapid AoR dilation or referral for aortic root surgery were identified. Further investigation may determine whether generalized proximal aortic dilation and effacement of the sinotubular junction will allow for better risk stratification. Rate of AoR dilation cut-points had high specificity, but low sensitivity for predicting referral for aortic surgery, limiting their clinical use. Clinical Trial Number ClinicalTrials.gov number, NCT00429364

The Carnegie Supernova Project: First Near-Infrared Hubble Diagram to z~0.7

The Carnegie Supernova Project (CSP) is designed to measure the luminosity distance for Type Ia supernovae (SNe Ia) as a function of redshift, and to set observational constraints on the dark energy contribution to the total energy content of the Universe. The CSP differs from other projects to date in its goal of providing an I-band {rest-frame} Hubble diagram. Here we present the first results from near-infrared (NIR) observations obtained using the Magellan Baade telescope for SNe Ia with 0.1 < z < 0.7. We combine these results with those from the low-redshift CSP at z <0.1 (Folatelli et al. 2009). We present light curves and an I-band Hubble diagram for this first sample of 35 SNe Ia and we compare these data to 21 new SNe Ia at low redshift. These data support the conclusion that the expansion of the Universe is accelerating. When combined with independent results from baryon acoustic oscillations (Eisenstein et al. 2005), these data yield Omega_m = 0.27 +/- 0.0 (statistical), and Omega_DE = 0.76 +/- 0.13 (statistical) +/- 0.09 (systematic), for the matter and dark energy densities, respectively. If we parameterize the data in terms of an equation of state, w, assume a flat geometry, and combine with baryon acoustic oscillations, we find that w = -1.05 +/- 0.13 (statistical) +/- 0.09 (systematic). The largest source of systematic uncertainty on w arises from uncertainties in the photometric calibration, signaling the importance of securing more accurate photometric calibrations for future supernova cosmology programs. Finally, we conclude that either the dust affecting the luminosities of SNe Ia has a different extinction law (R_V = 1.8) than that in the Milky Way (where R_V = 3.1), or that there is an additional intrinsic color term with luminosity for SNe Ia independent of the decline rate.Comment: 44 pages, 23 figures, 9 tables; Accepted for publication in the Astrophysical Journa

The Peculiar SN 2005hk: Do Some Type Ia Supernovae Explode as Deflagrations?

We present extensive u'g'r'i'BVRIYJHKs photometry and optical spectroscopy of SN 2005hk. These data reveal that SN 2005hk was nearly identical in its observed properties to SN 2002cx, which has been called ``the most peculiar known type Ia supernova.'' Both supernovae exhibited high ionization SN 1991T-like pre-maximum spectra, yet low peak luminosities like SN 1991bg. The spectra reveal that SN 2005hk, like SN 2002cx, exhibited expansion velocities that were roughly half those of typical type Ia supernovae. The R and I light curves of both supernovae were also peculiar in not displaying the secondary maximum observed for normal type Ia supernovae. Our YJH photometry of SN 2005hk reveals the same peculiarity in the near-infrared. By combining our optical and near-infrared photometry of SN 2005hk with published ultraviolet light curves obtained with the Swift satellite, we are able to construct a bolometric light curve from ~10 days before to ~60 days after B maximum. The shape and unusually low peak luminosity of this light curve, plus the low expansion velocities and absence of a secondary maximum at red and near-infrared wavelengths, are all in reasonable agreement with model calculations of a 3D deflagration which produces ~0.25 M_sun of 56Ni.Comment: Accepted by PASP, to appear in April 2007 issue, 63 pages, 16 figures, 11 table