977 resultados para Error-correcting Codes


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In studies of cognitive processing, the allocation of attention has been consistently linked to subtle, phasic adjustments in autonomic control. Both autonomic control of heart rate and control of the allocation of attention are known to decline with age. It is not known, however, whether characteristic individual differences in autonomic control and the ability to control attention are closely linked. To test this, a measure of parasympathetic function, vagal tone (VT) was computed from cardiac recordings from older and younger adults taken before and during performance of two attentiondemanding tasks - the Eriksen visual flanker task and the source memory task. Both tasks elicited event-related potentials (ERPs) that accompany errors, i.e., error-related negativities (ERNs) and error positivities (Pe's). The ERN is a negative deflection in the ERP signal, time-locked to responses made on incorrect trials, likely generated in the anterior cingulate. It is followed immediately by the Pe, a broad, positive deflection which may reflect conscious awareness of having committed an error. Age-attenuation ofERN amplitude has previously been found in paradigms with simple stimulus-response mappings, such as the flanker task, but has rarely been examined in more complex, conceptual tasks. Until now, there have been no reports of its being investigated in a source monitoring task. Age-attenuation of the ERN component was observed in both tasks. Results also indicated that the ERNs generated in these two tasks were generally comparable for young adults. For older adults, however, the ERN from the source monitoring task was not only shallower, but incorporated more frontal processing, apparently reflecting task demands. The error positivities elicited by 3 the two tasks were not comparable, however, and age-attenuation of the Pe was seen only in the more perceptual flanker task. For younger adults, it was Pe scalp topography that seemed to reflect task demands, being maximal over central parietal areas in the flanker task, but over very frontal areas in the source monitoring task. With respect to vagal tone, in the flanker task, neither the number of errors nor ERP amplitudes were predicted by baseline or on-task vagal tone measures. However, in the more difficult source memory task, lower VT was marginally associated with greater numbers of source memory errors in the older group. Thus, for older adults, relatively low levels of parasympathetic control over cardiac response coincided with poorer source memory discrimination. In both groups, lower levels of baseline VT were associated with larger amplitude ERNs, and smaller amplitude Pe's. Thus, low VT was associated in a conceptual task with a greater "emergency response" to errors, and at the same time, reduced awareness of having made them. The efficiency of an individual's complex cognitive processing was therefore associated with the flexibility of parasympathetic control of heart rate, in response to a cognitively challenging task.

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Event-related potentials were recorded from 10-year-old children and young adults in order to examine the developmental dififerences in two frontal lobe functions: detection of novel stimuli during an auditory novelty oddball task, and error detection during a visual flanker task. All participants showed a parietally-maximal P3 in response to auditory stimuli. In children, novel stimuli generated higher P3 amplitudes at the frontal site compared with target stimuli, whereas target stimuli generated higher P3 amplitudes at the parietal site compared with novel stimuli. Adults, however, had higher P3 amplitude to novel tones compared with target tones at each site. Children also had greater P3 amplitude at more parietal sites than adults during the novelty oddball and flanker tasks. Furthermore, children and adults did not show a significant reduction in P3 amplitude from the first to second novel stimulus presentation. No age differences were found with respect to P3 latency to novel and target stimuli. These findings suggest that the detection of novel and target stimuli is mature in 10-year-olds. Error trials typically elicit a negative ERP deflection (the ERN) with a frontal-central scalp distribution that may reflect response monitoring. There is also evidence of a positive ERP peak (the Pe) with a posterior scalp distribution which may reflect subjective recognition of a response. Both children and adults showed an ERN and Pe maximal at frontal-central sites. Children committed more errors, had smaller ERN across sites, and had a larger Pe at the parietal site than adults. This suggests that response monitoring is still immature in 10-year-olds whereas recognition of and emotional responses to errors may be similar in children and adults.

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The design of a large and reliable DNA codeword library is a key problem in DNA based computing. DNA codes, namely sets of fixed length edit metric codewords over the alphabet {A, C, G, T}, satisfy certain combinatorial constraints with respect to biological and chemical restrictions of DNA strands. The primary constraints that we consider are the reverse--complement constraint and the fixed GC--content constraint, as well as the basic edit distance constraint between codewords. We focus on exploring the theory underlying DNA codes and discuss several approaches to searching for optimal DNA codes. We use Conway's lexicode algorithm and an exhaustive search algorithm to produce provably optimal DNA codes for codes with small parameter values. And a genetic algorithm is proposed to search for some sub--optimal DNA codes with relatively large parameter values, where we can consider their sizes as reasonable lower bounds of DNA codes. Furthermore, we provide tables of bounds on sizes of DNA codes with length from 1 to 9 and minimum distance from 1 to 9.

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The purpose of the present study was to determine which augmented sensory modality would best develop subjective error-detection capabilities of learners performing a spatial-temporal task when using a touch screen monitor. Participants were required to learn a 5-digit key-pressing task in a goal time of 2550 ms over 100 acquisition trials on a touch screen. Participants were randomized into 1 of 4 groups: 1) visual-feedback (colour change of button when selected), 2) auditory-feedback (click sound when button was selected), 3) visual-auditory feedback (both colour change and click sound when button was selected), and 4) no-feedback (no colour change or click sound when button was selected). Following each trial, participants were required to provide a subjective estimate regarding their performance time in relation to the actual time it took for them complete the 5-digit sequence. A no-KR retention test was conducted approximately 24-hours after the last completed acquisition trial. Results showed that practicing a timing task on a touch screen augmented with both visual and auditory information may have differentially impacted motor skill acquisition such that removal of one or both sources of augmented feedback did not result in a severe detriment to timing performance or error detection capabilities of the learner. The present study reflects the importance of multimodal augmented feedback conditions to maximize cognitive abilities for developing a stronger motor memory for subjective error-detection and correction capabilities.

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Letter to S.D. Woodruff from an illegible signature stating that he suspects a clerical error in one of the columns, n.d.

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UANL

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This note develops general model-free adjustment procedures for the calculation of unbiased volatility loss functions based on practically feasible realized volatility benchmarks. The procedures, which exploit the recent asymptotic distributional results in Barndorff-Nielsen and Shephard (2002a), are both easy to implement and highly accurate in empirically realistic situations. On properly accounting for the measurement errors in the volatility forecast evaluations reported in Andersen, Bollerslev, Diebold and Labys (2003), the adjustments result in markedly higher estimates for the true degree of return-volatility predictability.

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