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Results for “Contrastive learning”

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At least 199 records · Page 11Linked to original sources

PubMed2001

Rationale for training programs to reduce anterior cruciate ligament injuries in Australian football.

This commentary presents the rationale for training programs to reduce the incidence of knee injuries. Our studies have revealed that the external knee loading patterns during sidestep cutting are what put the anterior cruciate ligament at greatest risk for injury. Compared to running, sidestep cutting involves similar levels of knee flexion loading but increased loading in varus-valgus and internal rotation of the knee, and these external loads need to be stabilized or supported by the internal structures of the knee. People use a generalized hamstrings and quadriceps co-contraction to stabilize these external loads, thereby reducing ligament loading. It is proposed that perturbation of the joint receptors reinforces the use of selective hamstrings and quadriceps co-contraction patterns superimposed on a generalized co-contraction pattern. This is not by immediate ligamento-muscular protective reflex, which is too slow to provide any adequate support, but by enhanced proprioceptive information that may be used in learning. In contrast, the immediate effect of muscle stretch reflexes would be to reduce co-contraction, a possibly negative outcome for joint stabilization. The effects of different types of training on the control of joint stability are examined. It is proposed that resistance training may not be appropriate because it enhances muscle stretch reflexes, which may reduce co-contraction, and produces no reductions in voluntary activation times and time to peak torque. However, stability and balance training is thought to suppress muscle stretch reflexes and, in turn, enhance co-contraction. Also, stability and balance training that stimulates the knee joint ligament and capsular receptors may reinforce co-contraction patterns to facilitate greater improvements in joint stabilization. Stability and balance training and plyometric training produce reductions in voluntary activation times and times to peak torque, which may decrease muscle response times so players are more able to perform rapid and unexpected sports maneuvers. Training programs that emphasize these neuromuscular mechanisms may enhance protection of the anterior cruciate ligament and reduce the incidence of injury.

Anterior Cruciate Ligament↗

PubMed2003

Use of interactive online histopathology modules at different stages of a veterinary program.

A mixed-method educational research study was conducted to evaluate the use of a series of online histopathology modules by students at two levels in a professional veterinary medical program. The materials were hypothesized to support student learning of histopathology concepts by facilitating "dual coding" of the content, since they provide both visual and verbal information. Second- and fourth-year professional veterinary students were surveyed about their perceptions of the effectiveness, efficiency, and appeal of the online modules. A historical comparison of final grades in the second-year Pathology course was conducted to evaluate the impact of the materials on academic outcomes. Think-aloud interviews were conducted with the fourth-year students in which the researcher observed the students interacting with the materials and asked them to "tell me what you're thinking as you use the modules." Survey results show that the only area in which the two student groups quantitatively rated the materials differently was their perception of how the materials complemented their learning. In contrast, the qualitative data indicate that advanced students used and perceived the materials differently, perhaps because of their greater metacognitive skills and pre-existing knowledge. We concluded that these findings can be attributed to the manner in which students approached the materials: the fourth-year students felt the materials were less relevant because they did not directly correspond to cases they were seeing, while the second-year students appreciated their relevance to topics in the Pathology course. There was no significant difference in final exam performance for the group of students that used the supplemental online modules and the prior four years' classes, who did not have access to the materials. Overall, this study demonstrated that it is possible to create a set of materials to be used by multiple audiences, provided the needs of each group are taken into consideration during the design process.

Animals↗

PubMed2006

Extinction of conditioned inhibition through nonreinforced presentation of the inhibitor.

In previous studies that have tried to extinguish conditioned inhibition through nonreinforced presentations of the inhibitor, researchers have repeatedly failed to find evidence for such extinction. The present study revealed that extinction can be achieved through nonreinforcement of the inhibitor, depending on properties of the reinforcer. In a human causal learning experiment, we found complete extinction in a scenario in which the reinforcer could take on negative values. Thereby, this scenario reflected the assumed symmetrical continuum on which associative strength can vary, according to the Rescorla-Wagner theory of associative learning. In contrast to this, the inhibitory cue retained its inhibitory potential in another condition, in which the scenario did not allow negative values of the reinforcer.

Attention↗

PubMed2002

[Expected practical clinical skills and newly qualified physicians].

INTRODUCTION: We compared and contrasted the learned and intended practical clinical skills of the three Danish medical schools. MATERIAL AND METHODS: An anonymous questionnaire listing 210 practical clinical skills was posted to 226 newly qualified Danish physicians. They were asked if they could meet the minimum level for each of the skills, which had earlier been identified by a Delphi study. RESULTS: The response rate was 80%. None of the responders met the minimum of all the 210 skills. Only 8% (14) met the minimum level for at least 90% (189) of the skills. On average, the responders met the minimum for 74% (155) of the skills. More than 90% of the responders could take medical histories and carry out examinations. The responders did not meet 28 medical emergency procedures. DISCUSSION: We found that the clinical skills learned constituted 75% of those intended. Those responsible for pre- and postgraduate medical training should be aware of the discrepancy between expected and learned skills. We discuss the role of experts in the process of defining the core curriculum.

Clinical Competence↗

PubMed2002

The two paradigms of persistence.

Persistence refers to the extent to which an individual pursues reinforcement that is no longer available. The most common generalization regarding persistence is the partial reinforcement extinction effect, which states that partial, rather than continuous, reinforcement creates the greatest level of persistence. Although the partial reinforcement effect is the most common effect in humans, exceptions exist, namely the generalized and the reversed partial reinforcement effect. Since the 1930s, psychologists have used 2 general paradigms for studying persistence in humans: the experimental paradigm and the cognitive/individual differences paradigm. For the experimental paradigm, the primary independent variable is the schedule of reinforcement used to establish the behavior prior to the removal of reinforcement. Explanations of persistence from the experimental perspective depend on associative principles derived from various theories of learning. By contrast, the cognitive/individual differences paradigm treats persistence as a function of trait variables, including locus of control and self-esteem, or general cognitive processes, such as cognitive dissonance or social cognition. In this article, the author reviews the status of the current literature on persistence and recommends directions for future research.

Cognition↗

PubMed2004

Motion detection and prediction through spike-timing dependent plasticity.

We describe a possible mechanism for the formation of direction- and velocity-selective cells in visual cortex through spike-timing dependent learning. We contrast the case where only feedforward excitation and inhibition signals are provided to visual neurons with the case where both feedforward and feedback signals are provided. In the feedforward-only case, neurons become selective for a broad range of velocities centered around the training velocity. However, we show that direction selectivity in this case is strongly dependent on delayed feedforward inhibition and in contrast to experimental results, becomes dramatically weaker when inhibition is reduced. When feedback connections are introduced, direction selectivity becomes much more robust due to predictive delays encoded in recurrent activity. Direction selectivity persists in the face of decreasing inhibition in a manner similar to experimental findings. The model predicts that direction-selective cells should exhibit anticipatory activity due to recurrent excitation and suggests a pivotal role for spike-timing dependent plasticity in shaping cortical circuits for visual motion detection and prediction.

Action Potentials↗

PubMed1983

Developmental milestones: sign language acquisition and motor development.

The sign language and motor development of 11 young children of deaf parents were studied across a 16-month period. The subjects showed accelerated early language development producing, on the average, their first recognizable sign at 8.5 months, their tenth sign at 13.2 months, and their first sign combination at 17.0 months. In contrast, children learning to speak typically do not attain the equivalent spoken language milestones until 2-3 months later. The structure and content of the subjects' 50-sign vocabularies closely resembled those for children at the same stage in previously published studies of spoken language acquisition. The pattern of synchrony between motor and language development previously reported by investigators of children learning to speak was found not to apply to the population of the present study: most of the subjects learning to sign did not slow down in their rate of language acquisition after achieving a new motor milestone, but rather continued to show a gradual increase in the size of their sign language vocabularies.

Child Development↗

PubMed2003

Behavioural and emotional characteristics in children with Sotos syndrome and learning disabilities.

In contrast to physical characteristics, the developmental and behavioural characteristics of children with Sotos syndrome are not well documented. Data from a survey of 27 children (17 males and 10 females; mean age 10 years 7 months; range 6 to 15 years) with mild and moderate learning disabilities were obtained concerning school placement, social networks, adaptive competence, and behavioural problems and compared with a control group matched for cognitive level and age. Ten children attended a mainstream school (with remedial assistance), eight were placed in a school for children with learning disabilities, nine children attended other special schools. Social contact problems and anxious behaviour were reported as the most prominent characteristics of children with Sotos syndrome. Some implications for psychological counselling and educational support are discussed.

Achievement↗

PubMed1975

Ego strength and confidence thresholds in two methods of paired-associate learning.

Two experiments contrasted the effects of high and low wgo strength (as measured by Cattell's Sixteen Personality Factor Questionaire) on confidence thresholds (FG scores) under the anticipation and recall methods. High ego strength resulted in larger FG scores under the anticipation method- weakly so in Experiment I but significantly so in Experiment II, where subjects were selected from greater extremes of ego strength. This inferiority extended to trails to criterion and a measure of the associative-learning stage as well. Tasks for extending the generality of the obtained relationship of ego strength and confidence thresholds in paired-associate learning are suggested.

Adolescent↗

PubMed2002

Distinguishing prototype-based and exemplar-based processes in dot-pattern category learning.

The authors contrast exemplar-based and prototype-based processes in dot-pattern categorization. In Experiments 1A and 1B, participants provided similarity ratings of dot-distortion pairs that were distortions of the same originating prototype. The results show that comparisons to training exemplars surrounding the prototype create flat typicality gradients within a category and small prototype-enhancement effects, whereas comparisons to a prototype center create steep typicality gradients within a category and large prototype-enhancement effects. Thus, prototype and exemplar theories make different predictions regarding common versions of the dot-distortion task. Experiment 2 tested these different predictions by having participants learn dot-pattern categories. The steep typicality gradients, the large prototype effects, and the superior fit of prototype models suggest that participants refer to-be-categorized items to a representation near the category's center (the prototype), and not to the training exemplars that surround the prototype.

Attention↗

PubMed1977

Sequential contrast effects with retarded subjects after discrimination learning with and without errors.

Four retarded adults were exposed to a multiple variable interval-extinction schedule of reinforcement. The 2 min components were presented in a random order. Two subjects acquired the discrimination with an errorless procedure. The two other subjects learned the discrimination with errors. The schedule generated sequential contrast effects under both training procedures: response rates during periods of reinforcement were higher when a reinforcement period followed an extinction period than when it followed another reinforcement period. These results were confirmed in a second observation where eight retarded children were exposed to a multiple fixed ratio-extinction schedule of reinforcement. This study is the first demonstration of sequential contrast effects with human subjects during the acquisition of a discrimination without errors. The results are discussed in terms of Terrace's theory of errorless learning.

Adolescent↗

PubMed2000

Lower-extremity revascularisation without preoperative contrast arteriography in 185 cases: lessons learned with duplex ultrasound arterial mapping.

PURPOSE: we have previously reported our experience with lower-extremity duplex-ultrasound arterial mapping (DUAM) compared to contrast arteriography (CA) to predict lower-extremity bypass sites. The present study evaluates arterial revascularisation procedures for chronic limb ischaemia based on DUAM. MATERIALS AND METHODS: from January 1998 to July 1999, 195 patients (128 men, 67 women) underwent 211 lower-extremity revascularisation procedures based on DUAM. Indications for surgery were tissue loss, severe claudication, rest pain and popliteal aneurysm in 57%, 25%, 14% and 4% of the limbs, respectively. The mean age was 72+/-12 years and risk factors such as diabetes, hypertension, tobacco use, coronary artery and end-stage renal disease were present in 53%, 58%, 53%, 50% and 12% of the patients, respectively. Previous revascularisation procedures had been performed in 23% of the limbs. Preoperative evaluation consisted of DUAM alone (185) or of a combination of DUAM and CA (29 limbs). CA was deemed necessary due to a combination of technical difficulties that jeopardized adequate sonographic imaging and presence of disadvantaged run-off for medico-legal reasons. DUAM consisted of direct imaging of all major arteries from the distal aorta to the pedal circulation. Optimal inflow and outflow bypass anastomotic sites were selected according to a diagram based on DUAM. Adequacy of the inflow was additionally assessed by common-femoral-artery waveform and confirmed by intraoperative pressure measurements. Post-bypass CA was obtained to verify patency of the run-off. RESULTS: DUAM procedure time averaged 75+/-26 min. For patients who underwent only DUAM, the distal anastomosis was to the popliteal artery in 91 cases and to tibial or pedal arteries in 58 cases. Distal anastomosis was proximal to a significant lesion in two cases that required jump grafts. Cumulative patency rates at 1 and 3 months for popliteal bypasses were 96% and 90%, and for infrapopliteal bypasses 90% and 83%, respectively. Inflow procedures to the femoral artery, patch and balloon angioplasties accounted for the remaining 40 cases. Four primary amputations were performed after CA confirmed DUAM findings. CONCLUSIONS: contrary to general belief, these data show that high-quality arterial ultrasonography represents a safe alternative to preoperative CA, even for infrapopliteal bypasses. This non-invasive approach may be especially useful for patients with contrast allergy or impaired renal function.

Adult↗

PubMed2007

Learning about protein hydrogen bonding by minimizing contrastive divergence.

Defining the strength and geometry of hydrogen bonds in protein structures has been a challenging task since early days of structural biology. In this article, we apply a novel statistical machine learning technique, known as contrastive divergence, to efficiently estimate both the hydrogen bond strength and the geometric characteristics of strong interpeptide backbone hydrogen bonds, from a dataset of structures representing a variety of different protein folds. Despite the simplifying assumptions of the interatomic energy terms used, we determine the strength of these hydrogen bonds to be between 1.1 and 1.5 kcal/mol, in good agreement with earlier experimental estimates. The geometry of these strong backbone hydrogen bonds features an almost linear arrangement of all four atoms involved in hydrogen bond formation. We estimate that about a quarter of all hydrogen bond donors and acceptors participate in these strong interpeptide hydrogen bonds.

Amino Acids↗

PubMed2005

Successive negative contrast in one-way avoidance learning in female Roman rats.

The inbred RLA (Roman Low-Avoidance) and RHA (Roman High-avoidance) rat strains have been psychogenetically selected for rapid (RHA) vs. extremely poor acquisition (RLA) of two-way active avoidance. As a consequence of this selective breeding, RLA animals exhibit a higher level of emotionality that can be observed in many anxiety models. The present study was conducted in order to analyze the performance of female RLA, RHA and Wistar rats in a behavioral test of anxiety that involves the reduction of the magnitude of an expected reward: the negative contrast effect that is obtained in one-way avoidance learning by reducing the time spent in the safe compartment. To this aim, three groups of animals (30-1/RLA, 30-1/RHA and 30-1/W) were trained to avoid an electric foot-shock administered in a "danger" compartment, by running from this compartment to a "safe" compartment. We observed an impairment of the avoidance response when time spent in the safe compartment was reduced from 30 to 1 s, when 30-1/RLA and 30-1/W groups were compared with control groups that were trained with a constant safe time (1-1/RLA and 1-1/W, respectively). We also obtained significant differences between 30-1/RLA and 30-1/RHA groups in the postshift phase. These results indicate that RLA rats respond more negatively to the frustration triggered by the reduction in time spent in the safe compartment, suggesting that animal models based on negative contrast effects can be useful tools for studying the genetic basis of anxiety.

Animals↗

PubMed2005

[Effects of repetition and dual-task on output monitoring errors].

We investigated output-monitoring errors in a modified source-monitoring paradigm. Unlike the traditional paradigm that involves two phases, learning and monitoring, the modified paradigm involves three phases, learning, enactment, and monitoring. Three experiments produced two major findings. First, compared with the traditional paradigm, the modified paradigm produced fewer monitoring errors. Second, performing a dual-task during the enactment phase increased monitoring errors for the items that participants repeatedly enacted during the learning phase. In contrast, performing a dual-task during the learning phase did not influence monitoring errors. It only decreased the number of items that were enacted during the enactment phase. We concluded that monitoring errors are more likely to occur (a) when the modality of items matches between the learning and enactment phases (i.e., items are enacted during both phases), and (b) when a dual-task increases processing demands during the enactment phase.

Adult↗

PubMed2003

The developmental course of processing speed in children with and without learning disabilities.

This study contrasted the development of processing speed in children with and without learning disabilities. We examined whether the same global mechanism presumed to be responsible for the normal developmental improvement in processing speed might also be associated with the processing speed deficiencies observed in children with learning impairments. One hundred and twenty-two children with learning disabilities in reading and/or math and 206 non-disabled community controls participated. There were no differences in relation of age to the development of processing speed for children with and without learning disabilities. We interpreted these results as suggesting that the underlying etiologies for the normal developmental change in processing speed and for the relative deficiencies in processing speed seen among children with learning disabilities were different.

Adult↗

PubMed1997

Face recognition with multi-tone and two-tone photographic negatives.

The effects of photographic negatives on face recognition are often studied in two different ways--faces are learned and tested in photographic negatives (NN) or the contrast is reversed between learning and testing, i.e. they are learned in positives and tested in negatives (PN) or vice versa (NP). We have examined recognition performance for faces under these three conditions along with a control condition where faces were learned and tested in positives (PP). Using multi-tone face images, we found that the effect of photographic negatives was more pronounced in PN and NP than in NN. No differences were found between PN and NP or between NN and PP. When two-tone face images were used, recognition performance was worse in all conditions, except PP, when compared to the multi-tone counterparts. Our results show that contrast incongruency between learning and testing is the predominant factor affecting performance and that deficits in sensory coding or retention of negative face images are unlikely to be major factors. The advantage of multi-tone over two-tone negatives can be attributed to preserved facial information carried by the high-spatial-frequency components of the image.

Adolescent↗

PubMed1999

Effects of divided attention on perceptual and conceptual memory tests: an analysis using a process-dissociation approach.

In two experiments, the nature of the relation between attention available at learning and subsequent automatic and controlled influences of memory was explored. Participants studied word lists in full and divided encoding conditions. Memory for the word lists was then tested with a perceptually driven task (stem completion) in Experiment 1 and with a conceptually driven task (category association) in Experiment 2. For recall cued with word stems, automatic influences of memory derived using the process-dissociation procedure remained invariant across a manipulation of attention that substantially reduced conscious recollection for the learning episode. In contrast, for recall cued with category names, dividing attention at learning significantly reduced the parameter estimates representing both controlled and automatic memory processes. These findings were similar to those obtained using indirect test instructions. The results suggest that, in contrast to perceptual priming, conceptual priming may be enhanced by semantic processing, and this effect is not an artifact of contamination from conscious retrieval processes.

Adult↗