1,720,998 research outputs found
Can a competitive neural network explain selective attention in insect target tracking neurons?
No full textSmall target motion detecting (STMD) neurons in the dragonfly brain are neural correlates of a highly-specialized and ethologically-significant feature detection function, and the recent discovery of selective attention in STMDs has clear implications for the ability of dragonflies to track and pursue one target from among several. We used a biophysically-plausible neural network model, based on competitive units fed by NMDA-type synaptic inputs and including lateral feedback inhibition, to model these attentional effects in numerical simulations. With appropriate forward gain, the model displays a winner-takes-all behavior that partially captures the selective attention documented in electrophysiological recordings from STMDs. It cannot, however, explain the full range of results that have now been observed in wide-field STMDs, in particular a bias toward attention to targets dependent on their traversal of continuous trajectories.Patrick A. Shoemaker, Steven D. Wiederman, and David C. O’Carrol
Bio-inspired feature extraction and enhancement of targets moving against visual clutter during closed loop pursuit
No full textWe developed a biologically inspired model for detection and pursuit of small targets against complex backgrounds and tested it in a closed-loop flight arena. A winner-takes-all network of local feature detectors based on insect Small Target Motion Detector (STMD) neurons was used to direct the gaze of a camera mimicking the viewpoint of the pursuer in a series of small steps (saccades) whilst fixating the background. The output of a direction-selective network of 2nd order local motion correlators was then used to enhance the relative salience of features in the direction of travel of the winning feature. The combination of saccadic fixation and robust target-ground discrimination provided by the STMD front-end, with an attention-like 2nd order salience enhancement provided very reliable capture of tiny targets even in visually challenging scenarios.Kerry J. Halupka, Steven D. Wiederman, Benjamin S. Cazzolato, David C. O‘Carrol
Facilitation of dragonfly target-detecting neurons by slow moving features on continuous paths
Full text linkExtent: 29p.Dragonflies detect and pursue targets such as other insects for feeding and conspecific interaction. They have a class of neurons highly specialized for this task in their lobula, the “small target motion detecting” (STMD) neurons. One such neuron, CSTMD1, reaches maximum response slowly over hundreds of milliseconds of target motion. Recording the intracellular response from CSTMD1 and a second neuron in this system, BSTMD1, we determined that for the neurons to reach maximum response levels, target motion must produce sequential local activation of elementary motion detecting elements. This facilitation effect is most pronounced when targets move at velocities slower than what was previously thought to be optimal. It is completely disrupted if targets are instantaneously displaced a few degrees from their current location. Additionally, we utilize a simple computational model to discount the parsimonious hypothesis that CSTMD1's slow build-up to maximum response is due to it incorporating a sluggish neural delay filter. Whilst the observed facilitation may be too slow to play a role in prey pursuit flights, which are typically rapidly resolved, we hypothesize that it helps maintain elevated sensitivity during prolonged, aerobatically intricate conspecific pursuits. Since the effect seems to be localized, it most likely enhances the relative salience of the most recently “seen” locations during such pursuit flights.James R. Dunbier, Steven D. Wiederman, Patrick A. Shoemaker and David C. O’Carrol
Discrete implementation of biologically inspired image processing for target detection
No full textIn nature, systems which visually process the world around them, in computationally efficient manners, have evolved over millions of years. The brain of an insect, which is smaller than a grain of rice, and with less than a million neurons, can effectively engage in computationally challenging tasks. For example, visually detecting and discriminating small moving objects, which are embedded within a complex optical flow pattern (induced by ego-motion). This task has yet to be perfected by current image processing techniques, though recent research is taking inspiration from nature to do so, in creating biologically inspired models of insect vision. This paper presents the progress made on our previous computational model based on electrophysiological data of a class of cells called Small Target Motion Detection neurons (STMDs). This model was based in the continuous temporal domain with constraints imposed on the inputs to the model. Modifications to the model include re-implementation in the discrete domain, the addition of a more physiologically accurate log-normal filter, the inclusion of a Reichardt Correlator and the creation of the highly controllable virtual world as a front end to the model. Model outputs show that the target detecting characteristics of the previous continuous model are maintained, though in a form which is directly applicable to hardware implementation.Kerry J. Halupka, Steven D. Wiederman, Benjamin S. Cazzolato, David C. O'Carrollhttp://www.issnip.org/~issnip2011
Modelling the temporal response properties of an insect small target motion detector
No full textInsects are an excellent model system for investigating computational mechanisms evolved for the challenging task of visualising and tracking small moving targets. We examined a well categorised small target motion detector (STMD) neuron, the dragonfly centrifugal STMD 1 (CSTMD1). This neuron has an unusually slow response onset, with a time course in the order of hundreds of milliseconds. A parsimonious explanation for this slow onset would be temporal low-pass filtering. However other authors have dismissed this and instead proposed a facilitation mechanism derived from second order motion detectors. We tested the spatial locality of response to continuous motion on non-contiguous paths and found spatial discontinuities in otherwise continuous motion reset the neuronal response. We modelled an array of elementary motion detectors (EMDs) in the insect visual pathway. We found that whilst individual components of the response can be explained simply by modifying the properties of the EMDs, the neurons response considered as a whole requires further elaborations within the system such as the proposed second order motion pathway.James R. Dunbier, Steven D. Wiederman, Patrick A. Shoemaker and David C. O’Carrollhttp://www.issnip.org/~issnip2011/index.ht
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
- …
