1,720,968 research outputs found
The role of timing in the induction of neuromodulation in perceptual learning by transcranial electric stimulation
No full textBackground: Transcranial electric stimulation (tES) protocols are able to induce neuromodulation,
offering important insights to focus and constrain theories of the relationship between brain and
behavior. Previous studies have shown that different types of tES (i.e., direct current stimulation e tDCS,
and random noise stimulation e tRNS) induce different facilitatory behavioral effects. However to date is
not clear which is the optimal timing to apply tES in relation to the induction of robust facilitatory effects.
Objective/hypothesis: The goal of this work was to investigate how different types of tES (tDCS and tRNS)
can modulate behavioral performance in the healthy adult brain in relation to their timing of application.
We applied tES protocols before (offline) or during (online) the execution of a visual perceptual learning
(PL) task. PL is a form of implicit memory that is characterized by an improvement in sensory
discrimination after repeated exposure to a particular type of stimulus and is considered a manifestation
of neural plasticity. Our aim was to understand if the timing of tES is critical for the induction of
differential neuromodulatory effects in the primary visual cortex (V1).
Methods: We applied high-frequency tRNS, anodal tDCS and sham tDCS on V1 before or during the
execution of an orientation discrimination task. The experimental design was between subjects and
performance was measured in terms of d’ values.
Results: The ideal timing of application varied depending on the stimulation type. tRNS facilitated task
performance only when it was applied during task execution, whereas anodal tDCS induced a larger
facilitation if it was applied before task execution.
Conclusion: The main result of this study is the finding that the timing of identical tES protocols yields
opposite effects on performance. These results provide important guidelines for designing neuromodulation
induction protocols and highlight the different optimal timing of the two excitatory
techniques
Neuroplasticity induction in a perceptual learning task. Which is the best timing to apply tES?
No full textPlaticity effects in visual perception learning: a transcranical electrical stimulation (tES) study
No full textIs neural hyperpolarization by cathodal stimulation always detrimental at the behavioral level?
No full textCathodal transcranial direct current stimulation (c-tDCS) is usually considered an inhibitory stimulation. From a physiological perspective, c-tDCS induces hyperpolarization at the neural level. However, from a behavioral perspective, c-tDCS application does not always result in performance deterioration. In this work, we investigated the role of several important stimulation parameters (i.e., timing, presence of pauses, duration, and intensity) in shaping the behavioral effects of c-tDCS over the primary visual cortex. In Experiment 1, we applied c-tDCS at two different times (before or during an orientation discrimination task). We also studied the effects of pauses during the stimulation. In Experiments 2 and 3, we compared different durations (9 vs. 22 min) and intensities (0.75 vs. 1.5 mA) of stimulation. c-tDCS applied before task execution induced an improvement of performance, highlighting the importance of the activation state of the cortex. However, this result depended on the duration and intensity of stimulation. We suggest that the application of c-tDCS induces depression of cortical activity over a specific stimulated area; but to keep reactivity within given limits, the brain react in order to restore the equilibrium and this might result in increased sensitivity in visual performance. This is a further example of how the nervous system dynamically maintains a condition that permits adequate performance in different environments
Random noise stimulation improves neuroplasticity in perceptual learning
No full textPerceptual learning is considered a manifestation of neural plasticity in the human brain. We investigated brain plasticity mechanisms in a learning task using noninvasive transcranial electrical stimulation (tES). We hypothesized that different types of tES would have varying actions on the nervous system, which would result in different efficacies of neural plasticity modulation. Thus, the principal goal of the present study was to verify the possibility of inducing differential plasticity effects using two tES approaches [i.e., direct current stimulation (tDCS) and random noise stimulation (tRNS)] during the execution of a visual perceptual learning task
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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