1,720,966 research outputs found
EXPRESS: The effect of the Uznadze illusion is temporally dynamic in closed-loop but temporally constant in open-loop grasping
No full textAlthough it is known that the availability of visual feedback modulates grasping kinematics, it is unclear whether this extends to both the early and late stages of the movement. We tackled this issue by exposing participants to the Uznadze illusion (a medium stimulus appears larger or smaller after exposure to smaller or larger inducers). After seeing smaller or larger discs, participants grasped a medium disc with (closed-loop [CL]) or without (open-loop [OL]) visual feedback. Our main aim was to assess whether the time course of the illusion from the movement onset up to the grasp differed between OL and CL. Moreover, we compared OL and CL illusory effects on maximum grip aperture (MGA) and tested whether preparation time, movement time, and time to MGA predicted illusion magnitude. Results revealed that CL illusory effects decreased over movement time, whereas OL ones remained constant. At the time of MGA, OL, and CL effects were, however, of similar size. Although OL grasps were longer to prepare and showed earlier and larger MGAs, such differences had little impact on modulating the illusion. These results suggest that the early stage of grasping is sensitive to the Uznadze illusion both under CL and OL conditions, whereas the late phase is sensitive to it only under OL conditions. We discuss these findings within the framework of theoretical models on the functional properties of the dorsal stream for visually guided actions
Action preparation in grasping reveals generalization of precision between implicit and explicit motor processes
No full textIt is often claimed that merely seeing a graspable object can elicit the implicit representation of a potential grasp. But can this representation affect the explicit execution of an actual grasp, and if so, how? In an open-loop paradigm, we instructed participants to grasp small, medium, or large test disks with the appropriate grip configuration (pincer, tripod, or pentapod). Before the presentation of these tests, we presented congruent or incongruent distractors. To assess interactions between implicit (putatively elicited by the distractors) and explicit (actually executed) sensorimotor processes, we measured preview reaction times (as an index of action preparation) and grasp kinematics (as an indicator of sensorimotor representations for motor control). Results indicate that action preparation is indeed affected by the presentation of preceding distractors. However, costs in action preparation were measured only when the first, implicit process was less precise than that of the actual grasp. We suggest that an interaction occurs at the level of sensorimotor processes through a mechanism which generalizes a precision parameter. We interpret these findings in relation to processes involved in real-time motor control and within the framework of theories of motor cognition
Action preparation in grasping reveals generalization of precision between implicit and explicit motor processes
No full textIt is often claimed that merely seeing a graspable object can elicit the implicit representation of a potential grasp. But can this representation affect the explicit execution of an actual grasp, and if so, how? In an open-loop paradigm, we instructed participants to grasp small, medium, or large test disks with the appropriate grip configuration (pincer, tripod, or pentapod). Before the presentation of these tests, we presented congruent or incongruent distractors. To assess interactions between implicit (putatively elicited by the distractors) and explicit (actually executed) sensorimotor processes, we measured preview reaction times (as an index of action preparation) and grasp kinematics (as an indicator of sensorimotor representations for motor control). Results indicate that action preparation is indeed affected by the presentation of preceding distractors. However, costs in action preparation were measured only when the first, implicit process was less precise than that of the actual grasp. We suggest that an interaction occurs at the level of sensorimotor processes through a mechanism which generalizes a precision parameter. We interpret these findings in relation to processes involved in real-time motor control and within the framework of theories of motor cognition
Asymmetric effects of graspable distractor disks on motor preparation of successive grasps: A behavioural and event-related potential (ERP) study
No full textThere is evidence that seeing a graspable object automatically elicits a preparatory motor process. However, it is unclear whether this implicit visuomotor process might influence the preparation of a successive grasp for a different object. We addressed the issue by implementing a combined behavioural and electrophysiological paradigm. Participants performed pantomimed grasps directed to small or large disks with either a two (pincer) or a five-finger (pentapod) grip, after the presentation of congruent (same size) or incongruent (different size) distractor disks. Preview reaction times (PRTs) and response-locked lateralized readiness potentials (R-LRPs) were recorded as online indices of motor preparation. Results revealed asymmetric effects of the distractors on PRTs and R-LRPs. For pincer grip disks, incongruent distractors were associated with longer PRTs and a delayed R-LRP peak. For pentapod grip disks, conversely, incongruent distractors were associated with shorter PRTs and a delayed R-LRP onset. Supporting an interpretation of these effects as tapping into motor preparation, we did not observe modulations of stimulus-locked LRP's (sensitive to sensory processing), or of the P300 component (related to reallocating attentional resources). These results challenge models (i.e., the “dorsal amnesia” hypothesis) which assume that visuomotor information presented before a grasp will not affect how we later perform that grasp
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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