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Thomas trappenberg

Cameron D Hassall, Patrick C Connor, Thomas P Trappenberg, John J McDonald, Olave E Krigolson
The visual environment is filled with complex, multi-dimensional objects that vary in their value to an observer's current goals. When faced with multi-dimensional stimuli, humans may rely on biases to learn to select those objects that are most valuable to the task at hand. Here, we show that decision making in a complex task is guided by the sparsity bias: the focusing of attention on a subset of available features. Participants completed a gambling task in which they selected complex stimuli that varied randomly along three dimensions: shape, color, and texture...
May 2018: International Journal of Psychophysiology
Farzaneh S Fard, Paul Hollensen, Dietmar Heinke, Thomas P Trappenberg
Humans can point fairly accurately to memorized states when closing their eyes despite slow or even missing sensory feedback. It is also common that the arm dynamics changes during development or from injuries. We propose a biologically motivated implementation of an arm controller that includes an adaptive observer. Our implementation is based on the neural field framework, and we show how a path integration mechanism can be trained from few examples. Our results illustrate successful generalization of path integration with a dynamic neural field by which the robotic arm can move in arbitrary directions and velocities...
December 2015: Neural Networks: the Official Journal of the International Neural Network Society
Patrick Connor, Paul Hollensen, Olav Krigolson, Thomas Trappenberg
Biological systems are capable of learning that certain stimuli are valuable while ignoring the many that are not, and thus perform feature selection. In machine learning, one effective feature selection approach is the least absolute shrinkage and selection operator (LASSO) form of regularization, which is equivalent to assuming a Laplacian prior distribution on the parameters. We review how such Bayesian priors can be implemented in gradient descent as a form of weight decay, which is a biologically plausible mechanism for Bayesian feature selection...
July 2015: Neural Networks: the Official Journal of the International Neural Network Society
Lauren Sculthorpe-Petley, Careesa Liu, Sujoy Ghosh Hajra, Hossein Parvar, Jason Satel, Thomas P Trappenberg, Rober Boshra, Ryan C N D'Arcy
BACKGROUND: Event-related potentials (ERPs) may provide a non-invasive index of brain function for a range of clinical applications. However, as a lab-based technique, ERPs are limited by technical challenges that prevent full integration into clinical settings. NEW METHOD: To translate ERP capabilities from the lab to clinical applications, we have developed methods like the Halifax Consciousness Scanner (HCS). HCS is essentially a rapid, automated ERP evaluation of brain functional status...
April 30, 2015: Journal of Neuroscience Methods
Pitoyo Hartono, Paul Hollensen, Thomas Trappenberg
Kohonen's self-organizing map (SOM) is used to map high-dimensional data into a low-dimensional representation (typically a 2-D or 3-D space) while preserving their topological characteristics. A major reason for its application is to be able to visualize data while preserving their relation in the high-dimensional input data space as much as possible. Here, we are seeking to go further by incorporating semantic meaning in the low-dimensional representation. In a conventional SOM, the semantic context of the data, such as class labels, does not have any influence on the formation of the map...
October 2015: IEEE Transactions on Neural Networks and Learning Systems
Patrick C Connor, Vincent M Lolordo, Thomas P Trappenberg
No abstract text is available yet for this article.
March 2014: Learning & Behavior
Dominic Standage, Thomas Trappenberg, Gunnar Blohm
It is widely accepted that the direction and magnitude of synaptic plasticity depends on post-synaptic calcium flux, where high levels of calcium lead to long-term potentiation and moderate levels lead to long-term depression. At synapses onto neurons in region CA1 of the hippocampus (and many other synapses), NMDA receptors provide the relevant source of calcium. In this regard, post-synaptic calcium captures the coincidence of pre- and post-synaptic activity, due to the blockage of these receptors at low voltage...
2014: PloS One
Patrick C Connor, Vincent M Lolordo, Thomas P Trappenberg
When retrospective revaluation phenomena (e.g., unovershadowing: AB+, then A-, then test B) were discovered, simple elemental models were at a disadvantage because they could not explain such phenomena. Extensions of these models and novel models appealed to within-compound associations to accommodate these new data. Here, we present an elemental, neural network model of conditioning that explains retrospective revaluation apart from within-compound associations. In the model, previously paired stimuli (say, A and B, after AB+) come to activate similar ensembles of neurons, so that revaluation of one stimulus (A-) has the opposite effect on the other stimulus (B) through changes (decreases) in the strength of the inhibitory connections between neurons activated by B...
March 2014: Learning & Behavior
Thomas Trappenberg, Paul Hollensen
While the target article provides a glowing account for the excitement in the field, we stress that hierarchical predictive learning in the brain requires sparseness of the representation. We also question the relation between Bayesian cognitive processes and hierarchical generative models as discussed by the target article.
June 2013: Behavioral and Brain Sciences
Robert A Marino, Thomas P Trappenberg, Michael Dorris, Douglas P Munoz
During natural vision, eye movements are dynamically controlled by the combinations of goal-related top-down (TD) and stimulus-related bottom-up (BU) neural signals that map onto objects or locations of interest in the visual world. In primates, both BU and TD signals converge in many areas of the brain, including the intermediate layers of the superior colliculus (SCi), a midbrain structure that contains a retinotopically coded map for saccades. How TD and BU signals combine or interact within the SCi map to influence saccades remains poorly understood and actively debated...
February 2012: Journal of Cognitive Neuroscience
Jason Satel, Thomas Trappenberg, Alan Fine
Synaptic plasticity is an underlying mechanism of learning and memory in neural systems, but it is controversial whether synaptic efficacy is modulated in a graded or binary manner. It has been argued that binary synaptic weights would be less susceptible to noise than graded weights, which has impelled some theoretical neuroscientists to shift from the use of graded to binary weights in their models. We compare retrieval performance of models using both binary and graded weight representations through numerical simulations of stochastic attractor networks...
September 2009: Cognitive Neurodynamics
Thomas Trappenberg
We discuss the ability of dynamic neural fields to track noisy population codes in an online fashion when signals are constantly applied to the recurrent network. To report on the quantitative performance of such networks we perform population decoding of the 'orientation' embedded in the noisy signal and determine which inhibition strength in the network provides the best decoding performance. We also study the performance of decoding on time-varying signals. Simulations of the system show good performance even in the very noisy case and also show that noise is beneficial to decoding time-varying signals...
September 2008: Cognitive Neurodynamics
Joshua P Salmon, Thomas P Trappenberg
Centre-Surround Neural Field (CSNF) models were used to explain a possible mechanism by which information from different sources may be integrated into target likelihood maps that are then used to direct eye saccades. The CSNF model is a dynamic model in which each region in network excites near-by location and inhibits distant locations, thereby modeling competition for eye movements (saccades). The CSNF model was tested in a number of conditions analogous to a naturalistic search task in which the target was either (1) present in the expected location, (2) present in the unexpected location, or (3) absent...
December 2008: Neural Networks: the Official Journal of the International Neural Network Society
Dominic Standage, Sajiya Jalil, Thomas Trappenberg
We present two weight- and spike-time dependent synaptic plasticity rules consistent with the physiological data of Bi and Poo (J Neurosci 18:10464-10472, 1998). One rule assumes synaptic saturation, while the other is scale free. We extend previous analyses of the asymptotic consequences of weight-dependent STDP to the case of strongly correlated pre- and post-synaptic spiking, more closely resembling associative learning. We further provide a general formula for the contribution of any number of spikes to synaptic drift...
June 2007: Biological Cybernetics
Dominic I Standage, Thomas P Trappenberg, Raymond M Klein
Experimental evidence on the distribution of visual attention supports the idea of a spatial saliency map, whereby bottom-up and top-down influences on attention are integrated by a winner-take-all mechanism. We implement this map with a continuous attractor neural network, and test the ability of our model to explain experimental evidence on the distribution of spatial attention. The majority of evidence supports the view that attention is unitary, but recent experiments provide evidence for split attentional foci...
June 2005: Neural Networks: the Official Journal of the International Neural Network Society
Edmund T Rolls, Simon M Stringer, Thomas P Trappenberg
Medial temporal lobe structures including the hippocampus are implicated by separate investigations in both episodic memory and spatial function. We show that a single recurrent attractor network can store both the discrete memories that characterize episodic memory and the continuous representations that characterize physical space. Combining both types of representation in a single network is actually necessary if objects and where they are located in space must be stored. We thus show that episodic memory and spatial theories of medial temporal lobe function can be combined in a unified model...
June 7, 2002: Proceedings. Biological Sciences
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