1,720,962 research outputs found
Modeling V1 complex cells in alert monkeys
No full textCortical complex cells are usually described as nonlinear energy operators that sum squared outputs of quadrature pairs of linear subunits, responding to drifting sinusoidal gratings with unmodulated elevation of flring rate (F0 harmonic). However, several lines of evidence suggest that the view of complex cells as a uniform class is over-simplifled, since energy models do not capture many complex cell behaviors. In alert monkeys complex cells with strongly overlapping increment and decrement regions exhibit a considerable F1 modulation, and a subset of these cells have a relative modulation (RM=F1/F0) >1. We have also found that most complex cells show profound dependence of the response form (harmonic content), and not only the amplitude, on grating parameters such as spatial and temporal frequency and size, displaying a variety of behaviors ranging from nonlinear unmodulated flring (F0) and frequency doubling (F2) to pseudolinear modulation (F1). One of the parsimonious explanations could be that at least some of these behaviors, e.g. F1 modulation, result from the imbalance of increment and decrement mechanisms such as incomplete spatial overlap and/or difierence in amplitudes of the two regions. We tested this hypothesis using a model that approximates an apparent structure of complex receptive flelds in our data by pooling two linear (increment and decrement) inputs with Gaussian spatial proflle and same biphasic temporal response function. Model cells with various overlaps and amplitude ratios were stimulated with drifting gratings of difierent spatial frequencies. To quantify the measure of spatial (im)balance we computed a product of overlap index and amplitude ratio. In the model, maximal modulation increased with spatial imbalance, and the correlation for the two measures was high (r=-0.86, p0.01) was inconsistent with model predictions. Thus, a static spatial imbalance of increment and decrement mechanisms cannot fully predict the presence of strong F1 harmonic in responses of complex cells. These results and efiects of temporal frequency suggest that temporal properties of input channels and possibly the dynamics of interaction between them play an important role in shaping the responses of complex cells. To account for the response diversity exhibited by complex cells, we are developing more realistic models that also include in∞uences of the surround
The influence of fixational eye movements on grating-elicited responses of V1 neurons
No full textIn alert monkeys, as in humans, small eye movements- tremor, drift and small saccades- occur during fixation periods. These movements constantly shift retinal image, thusmodifying the stimulus-generated responses. We analyzed the effects of eye movementson responses of simple and duplex (“complex-like”) cells to drifting sinusoidal gratings.Eye positions were recorded from monkeys trained to perform a fixation task. Duringfixation extracellular responses of V1 neurons in parafoveal region and eye positionswere recorded. From the eye position records we identified epochs of fast movements,slow drifts and stable fixation and compared patterns of neuronal firing during thevarious eye movement phases. Neuronal responses were sensitive to both fast and sloweye movements that occurred during grating presentations. In the case when no periodsof eye movements were excluded from the records, averaging across many repetitionsof the grating temporal cycle resulted in smearing of the response time course, althougheach individual sweep produced a modulated response. Eye movements affect neuronalresponses in a way that depends on eye movement trajectory, stimulus parameters andreceptive field properties. In particular, eye movements caused shifts in response phaseand/or duration, produced spurious firing bursts or caused cells to miss a response. Ourresults suggest that fixational eye movements account for variations in neuronalresponses over successive grating presentations and that these movements should beconsidered in analysis of grating-evoked activit
The influence of fixational eye movements on grating-elicited responses of V1 neurons
No full textIn alert monkeys, as in humans, small eye movements- tremor, drift and small saccades- occur during fixation periods. These movements constantly shift retinal image, thusmodifying the stimulus-generated responses. We analyzed the effects of eye movementson responses of simple and duplex (“complex-like”) cells to drifting sinusoidal gratings.Eye positions were recorded from monkeys trained to perform a fixation task. Duringfixation extracellular responses of V1 neurons in parafoveal region and eye positionswere recorded. From the eye position records we identified epochs of fast movements,slow drifts and stable fixation and compared patterns of neuronal firing during thevarious eye movement phases. Neuronal responses were sensitive to both fast and sloweye movements that occurred during grating presentations. In the case when no periodsof eye movements were excluded from the records, averaging across many repetitionsof the grating temporal cycle resulted in smearing of the response time course, althougheach individual sweep produced a modulated response. Eye movements affect neuronalresponses in a way that depends on eye movement trajectory, stimulus parameters andreceptive field properties. In particular, eye movements caused shifts in response phaseand/or duration, produced spurious firing bursts or caused cells to miss a response. Ourresults suggest that fixational eye movements account for variations in neuronalresponses over successive grating presentations and that these movements should beconsidered in analysis of grating-evoked activit
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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