Associative Processes in Statistical Learning: Paradoxical Predictions of the Past

The ability to process sequences of input and extract regularity across the distribution of input is fundamental for making predictions from the observed past to the future. Prediction is rooted in the extraction of both frequency- and conditional statistics from the distribution of inputs. For example, an animal hunting for food may consistently return to a particular area to hunt if relative to all other areas visited, that area has the highest frequency of prey. In contrast, humans asked to predict the next word in a sentence must make a prediction based upon higher-order regularities rather than simple frequency statistics (the most frequent word in the English language is the). The Serial Reaction Time (SRT) task, a model for studying sequential behavior, is used to quantify sensitivity to sequential constraints present in structured environments (Nissen & Bullemer, 1987). The SRT task requires Ss to make a unique response to each individually presented element from a sequence of elements. The statistics of SRT sequences, such as the relative frequency of elements and simple pairwise associations between elements, can be controlled to create dependencies that can only be predicted by learning higher-order associations. Sensitivity to the sequential constraints present in the structured input is demonstrated through differences in reaction time to elements that are, and are not, predictable based upon the statistics of the input environment. Sensitivity to statistical regularity in the environment is also a critical dimension of various episodic learning methodologies. Graded associations have been demonstrated among elements extending in both forward and backward directions in episodic memory tasks, and are suggested to reflect a gradient of the underlying structural relationships among the study elements. Graded associations are beneficial to the extent that they increase the probability of recalling sequence elements.However, unlike free and serial recall tasks, backward associations, and remote associations in general, are anti-predictive in the SRT task. The formation of associations beyond the immediately predictive element in prediction tasks could be suggestive of a ubiquitous underlying associative mechanism, which universally gives rise to graded contiguity effects, regardless of the specifc application (Howard, Jing, Rao, Provyn, & Datey, 2009). The following experiment employed a probabilistic SRT task to quantify sensitivity to immediately backward, backward-remote, and forward-remote associations. Ss were presented sequences of elements probabilistically sampled from an underlying ring-structure, with the dependent measure Ss\u27 reaction time to elements that either followed, or deviated from, the structure. Results from the SRT task indicated that Ss demonstrated a robust backward association, as well as evidence for forward-graded associations. Moreover, in an explicit test of sequence knowledge, while Ss did not generate the probabilistic statistics from the structured learning environment, Ss did generate a statistically signifcant amount of backward-transitions, relative to other remote-backward transitions. The graded associations that were formed beyond the immediately predictive element in the prediction task provide evidence that a similar mechanism that mediates episodic learning may also mediate statistical learning. Backward and graded associations may be explained by a ubiquitous underlying associative mechanism, which universally gives rise to graded contiguity effects, regardless of the specific application

Effects of Age on Contextually Mediated Associations in Paired Associate Learning

Older adults demonstrate an associative memory deficit that has been attributed to difficulty binding item information to contextual information (Naveh-Benjamin, 2000). Accounts of temporally-defined episodic associations that depend upon contextual retrieval (TCM Howard & Kahana, 2002) predict that a deficit in item-to-context binding will result in fewer backward (b-a) and transitive (a-c) associations. To measure group differences in backward and transitive associations, younger and older participants learned single function lists of paired associates with no contextual overlap (e.g., j-k, l-m) and double-function lists of paired associates consisting of chains of pairs (e.g., a-b, b-c). Although younger adults out-performed older adults on both pair types, there was a robust pair-type by age interaction. We suggest the older adults performed better than would be expected on the contextually overlapping double-function pairs due to an associative deficit in item-to-context binding, which resulted in the generation of fewer competing responses. Relative to younger adults, older adults made significantly more intrusions. Intrusion levels were normalized to equate for group differences and subsequent analysis indicated that younger adults made a larger proportion of associative intrusions to double-function probes than did older adults. The propensity of older adults to make fewer associative intrusions to double-function pairs suggests that older adults did not generate these associations. Thus, group differences in both correct recall probabilities and intrusion analysis suggest that backward and transitive associations are sensitive to aging. The results are discussed within the theoretical framework of the temporal context model and the hypothesis that older adults are impaired at forming new item-to-context associations

Reproducibility, accuracy and concordance of Accutrend® Plus for measuring circulating lipid concentration in adults

Introduction: The determination of lipid biomarkers by capillary sampling may be useful in the scree-ning, diagnosis and/or personal management of hyperlipidemia and cardiovascular risk. It remains unclear whether the use of the Accutrend® Plus system is appropriate. This study aimed to assess its reproducibility, accuracy and concordance for blood lipid profiling in adults. Materials and methods: Fasting capillary total cholesterol (TC) and triglyceride (TG) concentration on Accutrend® Plus were compared with their venous analogues obtained by a laboratory reference method in sixty-one adults (27 men and 34 women, aged 33.0 years). Supplementary capillary sam-pling was performed at two consecutive days taking into account macro-nutrient intake. Results: The day-to-day reproducibility of the Accutrend® Plus system proved to be high for TC (ICC = 0.85, P < 0.001), but moderate for TG (ICC = 0.68, P < 0.001). Strong correlations (r ≥ 0.80, P < 0.001) with the reference method were found for TC and TG. Mean difference (limits of agreement) were: 0.26 mmol/L (-0.95, 1.47) for TC, and -0.16 mmol/L (-1.29, 0.98) for TG. The concordance for subject classification according to the National Cholesterol Education Program (NCEP) guidelines was significant (P < 0.001), with substantial agreement for TC (κw = 0.67), and moderate agreement for TG (κw = 0.50). Conclusions: Day-to-day reproducibility of the Accutrend® Plus device for TC and TG is not optimal and lacks accuracy when compared to the reference laboratory method. The concordance between both methods for classifying subjects according to the NCEP is inadequate. Accutrend® Plus device should not be interchangeably used as a substitution for the standard laboratory methods in the diag-nosis of hyperlipidemia

Field study of anthropomorphic and muscle performance changes among elite skippers following a transoceanic race

Background: Ocean racing has become increasingly demanding, both physically and psychologically. The aim of the study was to assess global changes after a transoceanic race. Materials and methods: Eight male sailors were evaluated pre- and post-race through anthropometric measurements (weight, skinfold, girth at different level and estimated body fat percentage), multifrequency tetrapolar bioelectrical impedance, muscular performance, visual analogic scale for perceived fatigue and Critical Flicker Fusion Frequencies for cerebral arousal. Results: Compared to pre-race values, a significant decrease in body weight (–3.6 ± 1.4%, p = 0.0002) and body composition with reduction of body fat percentage (–15.1 ± 3.5%, p &lt; 0.0001) and fat mass (–36.4 ± 31.4%, p = 0.022) was observed. Muscle performance of the upper limb was preserved. In the lower limb, monohulls skippers showed a significant reduction of jump height (–6.6 ± 4.8%, p = 0.022), power (–11.7 ± 7.3%, p = 0.011) and speed (–14.6 ± 7.4%, p = 0.0006) while a multihulls skipper showed a gain in speed (+0.87%), power (+8.52%), force (+11%) resulting in a higher jump height (+1.12%). These changes were inversely correlated with sea days (Pearson r of –0.81, –0.96 and –0.90, respectively, p &lt; 0.01). Conclusions: Changes in body weight and composition are consistent with previous data indicating a probable negative energy balance. The main finding demonstrates a difference in muscular conditioning between upper and lower limbs that might be explained by differential workload related to boat architecture (trampolines) or handling

Ultrasound imaging of anatomical variations of humeral insertions of the subscapular muscle

Aims: The purpose of this study was to highlight the variations of the humeral insertion of the muscle in vivo, by means of an ultrasound (US) device to depict anatomical variations that could lead to instability of the scapulohumeral complex. Methods: This prospective study (IRB approval) brings a dynamic imaging of the anatomical variation by US exploration of 193 shoulders to confirm MRI and dissection approaches. Results: The results confirm the previous classification of two different classes of organization. 20% with a non-fibrous bridge over the intertubercular groove (type I and II combined) and 80% with a fibrous bridge over the tendon of the long head of the bicipital tendon muscle (type III and IV combined). Furthermore, statistical analysis (Fisher and Chi square test with a threshold of 95%) showed that this variation is not related to gender, side or laterality. Conclusion: This study shows the same results as obtained by dissection or MRI, meaning that this non-radiating, easy to perform technique can be used as a first approach in a dynamic clinical examination to detect anatomical variations of the subscapular muscle.</jats:p