1,721,999 research outputs found
Single cell responses in the ectostriatum of the zebra finch
No full textEngelage J, Bischof H-J. Single cell responses in the ectostriatum of the zebra finch. JOURNAL OF COMPARATIVE PHYSIOLOGY A-NEUROETHOLOGY SENSORY NEURAL AND BEHAVIORAL PHYSIOLOGY. 1996;179(6):785-795.The responses of single cells to computer-generated spots, bars, gratings, and motion-in-depth stimuli were studied in the ectostriatum and the adjacent neostriatum of the zebra finch, Taeniopygia guttata. No differences in neuronal properties could be detected between ectostriatum and neostriatum. The receptive fields of ectostriatal neurons are large, often extending over the entire visual field of the contralateral eye, and have oddly defined borders. The centers of the receptive fields, located in the foveal region, generally yielded better responses than the periphery, and exhibited different subdivisions. Neurons responded selectively to moving bars, preferring those moving parallel to their longest axis. An SDO (sensitivity, direction, orientation) analysis of responses to sinusoidal gratings showed that all orientations were equally represented by ectostriatal neurons, while there was a slight preference for forward and upward movements. The neurons also showed preferences for gratings of a particular spatial frequency, and responded vigorously to stimuli moving towards the eye (''looming''). Our results indicate that the ectostriatum is involved in both detecting displacement of the surround and in stimulus identification. By comparison with results obtained in the extrastriate cortex of mammals, it is concluded that the homology of the ectostriatum with the extrastriate cortex of mammals, which was proposed on the basis of hodological findings, is supported by our study
Single cell responses from the optic tectum of the zebra finch (Taeniopygia guttata castanotis Gould)
No full textSchmidt A, Engelage J, Bischof H-J. Single cell responses from the optic tectum of the zebra finch (Taeniopygia guttata castanotis Gould). JOURNAL OF COMPARATIVE PHYSIOLOGY A-SENSORY NEURAL AND BEHAVIORAL PHYSIOLOGY. 1999;185(1):69-79.Responses of neurons of the optic tectum, the prominent, highly laminated mesencephalic station of the tectofugal visual pathway in birds, to computer-generated and other visual stimuli were examined in zebra finches. Our study shows that the contralateral retina projects to the tectum in topographic order. The representation of the visual field is tilted against the horizon by 22 degrees. The representation of the contralateral hemifield extends to the ipsilateral side by 15 degrees. Most neurons have receptive fields with excitatory centres of different shapes and inhibitory surround. A hew type of neuronal receptive field is described which has an excitatory centre and a surround which is movement sensitive and preferably excited by very small spots. The first type of neurons is mostly located in upper tectal layers, the latter only in deeper layers. Excitatory centre sizes increase with depth, and there is a tendency of smaller receptive fields in the foveal region. The representation, of the frontal visual field does not show specializations which could be expected if it were used for fixation of grain during pecking. Our results are in accordance with previous behavioural experiments
Visual wulst influences on flash evoked responses in the ectostriatum of the zebra finch
Get PDFEngelage J, Bischof H-J. Visual wulst influences on flash evoked responses in the ectostriatum of the zebra finch. Brain Research. 1994;652(1):17-27.Anatomical data suggest that visual information from the thalamofugal pathway contributes to visual processing in the tectofugal pathway. We addressed the question of the functionality of anatomically described connections to the visual system of a laterally eyed bird, the zebra finch. The study shows the contribution of visual wulst efferents to visual processing in the ectostriatum by recordings of visually evoked slow field potentials. Suppression of visual wulst activity resulted in a selective reduction of distinct potential components in contralaterally evoked slow field potentials. A clear reduction was observed in the maximum amplitude of short latency components in the negative wave. Long latency components of the negative wave and the entire positive wave of the contralaterally flash evoked potentials were almost abolished. Ipsilateral visual evoked potentials (VEPs) were not significantly affected. Cooling and spreading depression of the optic tectum resulted in a uniform amplitude reduction of the negative wave. The positive wave was almost abolished. Ipsilateral VEPs disappeared completely during suppression of optic tectum activity. The results showed that the visual wulst has a significant, most likely facilitatory, influence on the processing of contralateral visual information in the ectostriatum. Ipsilateral stimulus processing was partly independent from visual wulst activity. A model for thalamo- and tectofugal connectivity in the ectostriatum is suggested
Visual system alterations in white zebra finches
No full textBredenkotter M, Engelage J, Bischof H-J. Visual system alterations in white zebra finches. BRAIN BEHAVIOR AND EVOLUTION. 1996;47(1):23-32.Visual system anomalies in albino mammals are generally seen to be caused by a lack of retinal pigment and misrouting of retinofugal optic fibers. This study shows that the central visual system of white zebra finches is physiologically different from normally colored (wild type) birds, although the eye pigmentation and the retinofugal projection appear to be normal. Ipsilaterally evoked potentials in our white birds are enhanced in comparison to wild type birds, whereas in albino mammals the ipsilateral component of visually evoked potentials is reduced. Picrotoxin-induced blockade of inhibitory synapses in the ectostriatum reveals remarkable differences between wild type and white zebra finches. In wild type zebra finches, a significant shift of ipsilateral to contralateral stimulus response ratios is observed. However, there is no detectable shift in the white morph. The data suggest that inhibition of ipsilateral stimulus processing, as observed in wild type zebra finches, is significantly reduced in the white morph. Our results indicate that the effects observed in white zebra finches cannot be explained by the theories that have been developed for albinotic animals. We assume that in white zebra finches a genetic defect, which causes the white plumage, is coupled with the demonstrated deviations of inhibitory mechanisms in the central visual system
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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