A test of Rescorla and Wagner’s (1972) prediction of nonlinear effects in contingency learning

According to most theories, in a simple contingency learning situation, excitatory learning occurs when the probability of the unconditioned stimulus in the presence of the conditioned stimulus (p₁) is higher than the probability of the unconditioned stimulus in the absence of the conditioned stimulus (p₂). In Rescorla and Wagner??s (1972) model, this prediction varies, depending on the parameters used. In the following experiments, we evaluated whether the difference between p₁ and p₂ that is required to produce excitatory conditioning is the same, independent of the specific value of p₁, or whether this difference varies proportionally to p₁??s value. To do so, an appetitive procedure of Pavlovian conditioning with rats was used. In four experiments, we compared different levels of contingency (low, medium and high) and found that the difference between p₁ and p₂ that is required to produce excitatory conditioning increases when the value of p₁ is higher. The possibility of analyzing contingency learning as a discrimination between p₁ and p₂ is also discussed.     

Reliability of force-velocity parameters obtained from linear and curvilinear regressions for the bench press and squat exercises

ABSTRACT

This study aimed to compare the goodness of fit and the reliability of different regression models for fitting the force-velocity relationship (FV) of bench press (BP) and squat (SQ). Additionally, the reliability of the position on FV of the velocity (V_1RM) and the force performed with the 1RM (F_1RM) was explored. Nine rugby players and 12 judokas participated in this study. The FV of BP and SQ were obtained twice by a protocol performed until the 1RM. Individual FV were fitted by linear (LM), quadratic polynomial (PM), and exponential models (EM). Adjusted coefficients of determination of LM and PM (medians higher than 0.919) were higher than for EM. The reliability was higher for LM in comparison with PM. The reliability of V_1RM was not acceptable (CV% = 19 and 18% for BP and SQ). High reliability was observed for F_1RM (CV% = 3 and 2% for BP and SQ) and for the ratio between F_1RM and the force-axis intercept of FV (CV% = 2 and 4% for BP and SQ). The reliability of the relative values of F_1RM around 92 and 87% of F₀ for BP and SQ suggests the use of these values for monitoring resistance training programmes.     

Unilateral and bilateral patellofemoral pain in young female dancers: Associated factors

ABSTRACT

Aiming to evaluate the prevalence of unilateral/bilateral patellofemoral pain (PFP) among young dancers, and to investigate whether different factors are associated with PFP in young dancers, 132 dancers aged 12–14 years were assessed for PFP. Anthropometric parameters, proprioception ability, dynamic postural balance (DPB), and muscle strength were measured. PFP was found in 64.1% of the dancers. No significant differences in the prevalence of dancers with no, unilateral, or bilateral PFP at different ages were found. Significant age effects were found for anthropometric and developmental measurements, and for intensity of training. PFP effect was found for DPB asymmetry, ankle proprioception, and leg-length %height. A higher hip abductor/adductor ratio was associated with PFP in 14-year-old dancers. Binomial logistic regression showed that increased number of hours per day (h/day) and decreased number of hours per week (h/week), low proprioception scores, greater leg length as %height, and more anterior DPB asymmetry were significant predictors of PFP. In conclusion: unilateral/bilateral PFP is common among young dancers. Body morphology, reduced ankle proprioception ability, DPB asymmetry, and increased h/day of practice are associated with PFP. Dance teachers should start monitoring the impact of training and implement injury modification/prevention strategies when their students are at a young age.     

Design approaches in technology-enhanced learning

Design is critical to the successful development of any interactive learning environment (ILE). Moreover, in technology-enhanced learning (TEL) the design process requires input from many diverse areas of expertise. As such, anyone undertaking tool development is required to directly address the design challenge from multiple perspectives. We provide a motivation and rationale for design approaches for learning technologies that draws upon Simon's seminal proposition of design science. We then review the application of design experiments and design patterns and argue that a patterns approach has the potential to address many of the critical challenges faced by learning technologists.     

From “Trust Me” to “Show Me” Journalism

This study explores the potential of an online platform that encourages journalists to post the documents behind their news stories to help restore the deteriorating public trust in news media. Based on content analysis of 200 news items and 315 accompanying documents posted on DocumentCloud, findings indicate that contrary to journalists’ traditional reluctance to rely on documents, the platform succeeds in boosting massive use of documents, both by mainstream and alternative journalists. Findings show that documents serve mainly to support factual claims (in 96 percent of items) and enhance the transparency of news processes, allowing audiences’ unmediated access to raw materials, and greater capacity to evaluate information independently. However, there are no apparent signs that journalists verified the content of the document. The article suggests that DocumentCloud is a unique example of a technology that may succeed where the former technology that promised to serve as a journalistic reference system, hyperlinks, had failed. If the DocumentCloud experiment is implemented on a wider scale, it might have serious theoretical and practical implications, which are discussed here.     

民族地区实现"以学生为中心"教学改革应注意的几个问题研究

本文通过对康定县瓦斯小学进行“以学生为中心”教学改革的实证分析，对“以学生为中心”的教育理念进行了重新解读。民族地区进行“以学生为中心”的教学改革应当做好五个方面的文章，实现四个方面的目标。实行“以学生为中心”的关键是转变教师角色；如果不稳定教师队伍和提高教师的素质，民族地区实现“以学生为中心”就会成为一句空话。“以学生为中心”的改革是一项任务艰巨而又意义重大的系统工程，不仅在教学上要进行改革，而且在学校管理、制度建设等方方面面都必须进行改革。     

Influence of stator slotting on the synchronous performance of the hysteresis machine

The influence of stator slotting on the synchronous performance of a hysteresis machine is analyzed on the basis of a rectified model of its structure. The stator block holding the windings in equally spaced slots is replaced by a fictitious block of iron with finite permeability whose value is defined in two relevant directions, namely, the longitudinal and the radial. This set-up has a definite influence on the writing of the boundary conditions for the fields in the machine and consequently on machine behaviour. On the basis of the presented results, an optimization procedure can be attempted for achieving the best performance.     

Velocity- and power-load relationships in the half,parallel and full back squat

This study aimed to compare the load-velocity and load-power relationships of three common variations of the squat exercise. 52 strength-trained males performed a progressive loading test up to the one-repetition maximum (1RM) in the full (F-SQ), parallel (P-SQ) and half (H-SQ) squat, conducted in random order on separate days. Bar velocity and vertical force were measured by means of a linear velocity transducer time-synchronized with a force platform. The relative load that maximized power output (Pmax) was analyzed using three outcome measures: mean concentric (MP), mean propulsive (MPP) and peak power (PP), while also including or excluding body mass in force calculations. 1RM was significantly different between exercises. Load-velocity and load-power relationships were significantly different between the F-SQ, P-SQ and H-SQ variations. Close relationships (R² = 0.92–0.96) between load (%1RM) and bar velocity were found and they were specific for each squat variation, with faster velocities the greater the squat depth. Unlike the F-SQ and P-SQ, no sticking region was observed for the H-SQ when lifting high loads. The Pmax corresponded to a broad load range and was greatly influenced by how force output is calculated (including or excluding body mass) as well as the exact outcome variable used (MP, MPP, PP).     

Extrinsic and intrinsic risk factors associated with injuries in young dancers aged 8-16 years

In the present study, we tried to determine the association between joint ranges of motion, anatomical anomalies, body structure, dance discipline, and injuries in young female recreational dancers. A group of 1336 non-professional female dancers (age 8-16 years), were screened. The risk factors considered for injuries were: range of motion, body structure, anatomical anomalies, dance technique, and dance discipline. Sixty-one different types of injuries and symptoms were identified and later classified into four major categories: knee injuries, foot or ankle tendinopathy, back injuries, and non-categorized injuries. We found that 569 (42.6%) out of the 1336 screened dancers, were injured.The following factors were found to be associated with injuries (P < 0.05): (a) range of motion (e.g. dancers with hyper hip abduction are more prone to foot or ankle tendinopathies than dancers with hypo range of motion; (b) anatomical anomalies (scoliotic dancers manifested a higher rate of injuries than non-scoliotic dancers); (c) dance technique (dancers with incorrect technique of rolling-in were found to have more injuries than dancers with correct technique); (d) dance discipline (an association between time of practice en pointe and injury was observed); and (e) early age of onset of menarche decreased risk for an injury. No association between body structure and injury was found. Injuries among recreational dancers should not be overlooked, and therefore precautionary steps should be taken to reduce the risk of injury, such as screening for joint range of motion and anatomical anomalies. Certain dance positions (e.g. en pointe) should be practised only when the dancer has already acquired certain physical skills, and these practices should be time controlled.