1,720,975 research outputs found
Static spatial effects in motor cortex and area 5: quantitative relations in a two-dimensional space.
No full textWe describe the relations between active maintenance of the hand at various positions in a two-dimensional space and the frequency of single cell discharge in motor cortex (n = 185) and area 5 (n = 128) of the rhesus monkey. The steady-state discharge rate of 124/185 (67\%) motor cortical and 105/128 (82\%) area 5 cells varied with the position in which the hand was held in space ("static spatial effect"). The higher prevalence of this effect in area 5 was statistically significant. In both structures, static effects were observed at similar frequencies for cells that possessed as well as for those that lacked passive driving from the limb. The results obtained by a quantitative analysis were similar for neurons of the two cortical areas studied. It was found that of the neurons with a static effect, the steady-state discharge rate of 78/124 (63\%) motor cortical and 63/105 (60\%) area 5 cells was a linear function of the position of the hand across the two-dimensional space, so that the neuronal "response surface" was adequately described by a plane (R2 greater than or equal to 0.7, p less than 0.05, F-test in analysis of variance). The preferred orientations of these response planes differed for different cells. These results indicate that individual cells in these areas do not relate uniquely a particular position of the hand in space. Instead, they seem to encode spatial gradients at certain orientations.(ABSTRACT TRUNCATED AT 250 WORDS
Cortical mechanisms related to the direction of two-dimensional arm movements: relations in parietal area 5 and comparison with motor cortex.
No full textThe relations between the direction of two-dimensional arm movements and single cell discharge in area 5 were investigated during 49 penetrations into the superior parietal lobule of 3 monkeys. A significant variation of cell discharge with the direction of movement was observed in 182 of 212 cells that were related to arm movements. In 151/182 of these cells the frequency of discharge was highest during movements in a preferred direction, and decreased in an orderly fashion with movements made in directions farther and farther away from the preferred one; in 112/151 cells this variation in discharge was a sinusoidal function of the direction of movement. Preferred directions differed for different cells so that directional tuning curves overlapped partially. These results are similar to those described for cells in the motor cortex (Georgopoulos et al. 1982): this suggests that directional information may be processed in a similar way in these structures. Many cells in area 5 changed activity before the onset of movement, and several did so before the earliest electromyographic changes (63\% and 35\%, respectively, of the cells that showed an increase in activity with movements in the preferred direction). However, the distribution of onset times of the parietal cells lagged the corresponding one of the motor cortical cells by about 60 ms. This suggests that the early changes observed in the parietal cortex might represent a corollary discharge from the precentral motor fields, whereas later activity might reflect peripheral as well as central events
Interruption of motor cortical discharge subserving aimed arm movements
No full textCan evolving motor commands be interrupted by changes in sensory signals that triggered them? We investigated this problem by observing the changes in single cell activity in the motor cortex of monkeys, changes that preceded movement of the hand toward a visual target. We found that this activity was interrupted following a shift of the target during the reaction or movement time and replaced by the pattern activity related to the movement towards the new target. This suggests that motor cortical commands subserving aimed arm movements are processes that can be interrupted in the course of their formation and/or execution by changes in afferent controlling inputs
On the relations between the direction of two-dimensional arm movements and cell discharge in primate motor cortex
No full text[No abstract available
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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