1,721,025 research outputs found
Probing human vision with spatial adaptation
No full textAdaptation to spatial displays has robust effects on the perception of visual stimuli presented after adaptation. Referred to as the ‘psychophysicist’s microelectrode’ (Frisby, 1979), spatial adaptation and aftereffects has proved to be a powerful technique in the investigation of the functional organization of the human visual system. Our 20 years of collaboration on spatial adaptation research in the hospitable atmosphere of Lothar Spillmann’s laboratory at the University of Freiburg has resulted in a number of experiments that we believe have contributed to the understanding of the mechanism of these short-lived plasticity effects, and to the understanding of the development of spatial channels in the human visual system. It was quickly realized that visual aftereffects could be explained by mechanisms at the cellular level (Barlow, 1972; Braddick et al., 1978), and our psychophysical experiments pointed to the, now accepted, explanation in terms of lateral inhibition between stimulus-specific neural channels (Ursino et al., 2008). It now appears that a similar mechanism governs higher-level adaptation to complex stimuli such as human faces.
The Gestalt psychologists described many of the figural aftereffects more than half century ago. It is appropriate that our research in this area was carried out in a German laboratory that so strongly continued the Gestalt tradition in perception research. Perception remains a mystery, but we now know a little more about the neural circuitry responsible for visual aftereffects, and we know a little more about ‘the way we see the world the way we do’ (Spillmann, 2009)
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
Two new density estimators for distance sampling
No full textTwo new density estimators for k-tree distance sampling are proposed and their performance is assessed in simulated distance sampling from 22 stem maps representing a wide range of natural to semi-natural forest tree stands with random to irregular (clustered) spatial distribution of trees. The new estimators are model-based. The first (Orbit) computes density as the inverse of the average of the areas associated with each of the k-trees nearest to a sample location. The area of the k-th tree is obtained as a prediction from a linear regression model while the area of the first is obtained via a Poisson probability integral. The second (GamPoi) is based on the expected distribution of distance to the k nearest tree in a forest where the local distribution of trees is random but the stem density varies from sample location to sample location as a gamma distribution. In a comprehensive assessment with 17 promising reference estimators, a subset composed of Morisita¿s, Persson¿s, Byth¿s, Kleinn¿s, Orbit, and GamPoi was significantly better, in terms of relative root mean square error (RRMSE), than average. GamPoi emerged as the better estimator for sample sizes larger than or equal to 30. For smaller sample sizes, both Kleinn¿s and Morisita¿s appear attractive
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
Saturation of the tilt aftereffect
Full text linkThe tilt aftereffect increases as a logarithmic function of adapting time, reaches saturation after approx 1 hr and decays on a symmetric, logarithmic time-course. This is similar to the time-course of contrast threshold elevation, suggesting that threshold and suprathreshold aftereffects are based on similar type of adaptation processes
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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