a b s t r a c t Emergent (http://grey.colorado.edu/emergent) is a powerful tool for the simulation of biologically plausible, complex neural systems that was released in August 2007. Inheriting decades of research and experience in network algorithms and modeling principles from its predecessors, PDP++ and PDP, Emergent has been redesigned as an efficient workspace for academic research and an engaging, easy-to-navigate environment for students. The system provides a modern and intuitive interface for programming and visualization centered around hierarchical, tree-based navigation and drag-anddrop reorganization. Emergent contains familiar, high-level simulation constructs such as Layers and Projections, a wide variety of algorithms, general-purpose data handling and analysis facilities and an integrated virtual environment for developing closed-loop cognitive agents. For students, the traditional role of a textbook has been enhanced by wikis embedded in every project that serve to explain, document, and help newcomers engage the interface and step through models using familiar hyperlinks. For advanced users, the software is easily extensible in all respects via runtime plugins, has a powerful shell with an integrated debugger, and a scripting language that is fully symmetric with the interface. Emergent strikes a balance between detailed, computationally expensive spiking neuron models and abstract, Bayesian or symbolic systems. This middle level of detail allows for the rapid development and successful execution of complex cognitive models while maintaining biological plausibility.

A paradigmatic test of executive control, the n-back task, is known to recruit a widely-distributed parietal, frontal and striatal “executive network,” and is thought to require an equally wide array of executive functions. The mapping of functions onto substrates in such a complex task presents a significant challenge to any theoretical framework for executive control. To address this challenge, we developed a biologically-constrained model of the n-back task that emergently develops the ability to appropriately gate, bind, and maintain information in working memory in the course of learning to perform the task. Furthermore, the model is sensitive to proactive interference in ways that match findings from neuroimaging, and shows a U-shaped performance curve after manipulation of prefrontal dopaminergic mechanisms similar to that observed in studies of genetic polymorphisms and pharmacological manipulations. Our model represents a formal computational link between anatomical, functional neuroimaging, genetic, behavioral, and theoretical levels of analysis in the study of executive control. In addition, the model specifies one way in which the prefrontal cortex, basal ganglia, parietal, and sensory cortices may learn to cooperate and give rise to executive control.

Abstract. Monocular figure-ground segmentation is an important problem in the field of Artificial General Intelligence. A solution to this problem will unlock vast sets of training data, such as Google Images, in which salient objects of interest are situated against complex backgrounds. In order to gain traction on the figure-ground problem we enhanced the Leabra Vision (LVis) model, which is our state-of-the-art model of 3D invariant object recognition [8], such that it can continue to recognize objects against cluttered backgrounds that, while simple, are complex enough to substantially hurt object recognition performance. The principle of operation of the network is that it learns to use a low resolution view of the scene in which high spatial frequency information such as the background falls out of focus in order to predict which aspects of the high resolution scene are the figure. This filtered view then serves to enhance the figure in the input stages of LVis and substantially improves object recognition performance against cluttered backgrounds.