Latest documents http://publikationen.ub.uni-frankfurt.de/index/index/ Thu, 21 Mar 2013 13:41:36 +0100 Thu, 21 Mar 2013 13:41:36 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/29148 The way we perceive the visual world depends crucially on the state of the observer. In the present study we show that what we are holding in working memory (WM) can bias the way we perceive ambiguous structure from motion stimuli. Holding in memory the percept of an unambiguously rotating sphere influenced the perceived direction of motion of an ambiguously rotating sphere presented shortly thereafter. In particular, we found a systematic difference between congruent dominance periods where the perceived direction of the ambiguous stimulus corresponded to the direction of the unambiguous one and incongruent dominance periods. Congruent dominance periods were more frequent when participants memorized the speed of the unambiguous sphere for delayed discrimination than when they performed an immediate judgment on a change in its speed. The analysis of dominance time-course showed that a sustained tendency to perceive the same direction of motion as the prior stimulus emerged only in the WM condition, whereas in the attention condition perceptual dominance dropped to chance levels at the end of the trial. The results are explained in terms of a direct involvement of early visual areas in the active representation of visual motion in WM. Lisa Scocchia; Matteo Valsecchi; Karl R. Gegenfurtner; Jochen Triesch article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/29148 Thu, 21 Mar 2013 13:41:36 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/28354 The information processing abilities of neural circuits arise from their synaptic connection patterns. Understanding the laws governing these connectivity patterns is essential for understanding brain function. The overall distribution of synaptic strengths of local excitatory connections in cortex and hippocampus is long-tailed, exhibiting a small number of synaptic connections of very large efficacy. At the same time, new synaptic connections are constantly being created and individual synaptic connection strengths show substantial fluctuations across time. It remains unclear through what mechanisms these properties of neural circuits arise and how they contribute to learning and memory. In this study we show that fundamental characteristics of excitatory synaptic connections in cortex and hippocampus can be explained as a consequence of self-organization in a recurrent network combining spike-timing-dependent plasticity (STDP), structural plasticity and different forms of homeostatic plasticity. In the network, associative synaptic plasticity in the form of STDP induces a rich-get-richer dynamics among synapses, while homeostatic mechanisms induce competition. Under distinctly different initial conditions, the ensuing self-organization produces long-tailed synaptic strength distributions matching experimental findings. We show that this self-organization can take place with a purely additive STDP mechanism and that multiplicative weight dynamics emerge as a consequence of network interactions. The observed patterns of fluctuation of synaptic strengths, including elimination and generation of synaptic connections and long-term persistence of strong connections, are consistent with the dynamics of dendritic spines found in rat hippocampus. Beyond this, the model predicts an approximately power-law scaling of the lifetimes of newly established synaptic connection strengths during development. Our results suggest that the combined action of multiple forms of neuronal plasticity plays an essential role in the formation and maintenance of cortical circuits. Pengsheng Zheng; Christos Dimitrakakis; Jochen Triesch article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/28354 Mon, 21 Jan 2013 12:45:47 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/24579 Infants' poor motor abilities limit their interaction with their environment and render studying infant cognition notoriously difficult. Exceptions are eye movements, which reach high accuracy early, but generally do not allow manipulation of the physical environment. In this study, real-time eye tracking is used to put 6- and 8-month-old infants in direct control of their visual surroundings to study the fundamental problem of discovery of agency, i.e. the ability to infer that certain sensory events are caused by one's own actions. We demonstrate that infants quickly learn to perform eye movements to trigger the appearance of new stimuli and that they anticipate the consequences of their actions in as few as 3 trials. Our findings show that infants can rapidly discover new ways of controlling their environment. We suggest that gaze-contingent paradigms offer effective new ways for studying many aspects of infant learning and cognition in an interactive fashion and provide new opportunities for behavioral training and treatment in infants. Quan Wang; Jantina Elizabeth Bolhuis; Constantin A. Rothkopf; Thorsten Kolling; Monika Knopf; Jochen Triesch article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/24579 Mon, 02 Apr 2012 11:42:33 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/23738 Various optimality principles have been proposed to explain the characteristics of coordinated eye and head movements during visual orienting behavior. At the same time, researchers have suggested several neural models to underly the generation of saccades, but these do not include online learning as a mechanism of optimization. Here, we suggest an open-loop neural controller with a local adaptation mechanism that minimizes a proposed cost function. Simulations show that the characteristics of coordinated eye and head movements generated by this model match the experimental data in many aspects, including the relationship between amplitude, duration and peak velocity in head-restrained and the relative contribution of eye and head to the total gaze shift in head-free conditions. Our model is a first step towards bringing together an optimality principle and an incremental local learning mechanism into a unified control scheme for coordinated eye and head movements. Sohrab Saeb; Cornelius Weber; Jochen Triesch article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/23738 Tue, 27 Dec 2011 00:00:00 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/22678 The influence of visual tasks on short and long-term memory for visual features was investigated using a change-detection paradigm. Subjects completed 2 tasks: (a) describing objects in natural images, reporting a specific property of each object when a crosshair appeared above it, and (b) viewing a modified version of each scene, and detecting which of the previously described objects had changed. When tested over short delays (seconds), no task effects were found. Over longer delays (minutes) we found the describing task influenced what types of changes were detected in a variety of explicit and incidental memory experiments. Furthermore, we found surprisingly high performance in the incidental memory experiment, suggesting that simple tasks are sufficient to instill long-lasting visual memories. Keywords: visual working memory, natural scenes, natural tasks, change detection Alan Robinson; Jochen Triesch article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/22678 Fri, 09 Sep 2011 14:06:47 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/22628 Average human behavior in cue combination tasks is well predicted by Bayesian inference models. As this capability is acquired over developmental timescales, the question arises, how it is learned. Here we investigated whether reward dependent learning, that is well established at the computational, behavioral, and neuronal levels, could contribute to this development. It is shown that a model free reinforcement learning algorithm can indeed learn to do cue integration, i.e. weight uncertain cues according to their respective reliabilities and even do so if reliabilities are changing. We also consider the case of causal inference where multimodal signals can originate from one or multiple separate objects and should not always be integrated. In this case, the learner is shown to develop a behavior that is closest to Bayesian model averaging. We conclude that reward mediated learning could be a driving force for the development of cue integration and causal inference. Thomas H. Weisswange; Constantin A. Rothkopf; Tobias Rodemann; Jochen Triesch article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/22628 Wed, 07 Sep 2011 09:15:35 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/20111 Although models based on independent component analysis (ICA) have been successful in explaining various properties of sensory coding in the cortex, it remains unclear how networks of spiking neurons using realistic plasticity rules can realize such computation. Here, we propose a biologically plausible mechanism for ICA-like learning with spiking neurons. Our model combines spike-timing dependent plasticity and synaptic scaling with an intrinsic plasticity rule that regulates neuronal excitability to maximize information transmission. We show that a stochastically spiking neuron learns one independent component for inputs encoded either as rates or using spike-spike correlations. Furthermore, different independent components can be recovered, when the activity of different neurons is decorrelated by adaptive lateral inhibition. Cristina Savin; Prashant Joshi; Jochen Triesch article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/20111 Tue, 26 Oct 2010 13:36:27 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/20110 Understanding the dynamics of recurrent neural networks is crucial for explaining how the brain processes information. In the neocortex, a range of different plasticity mechanisms are shaping recurrent networks into effective information processing circuits that learn appropriate representations for time-varying sensory stimuli. However, it has been difficult to mimic these abilities in artificial neural network models. Here we introduce SORN, a self-organizing recurrent network. It combines three distinct forms of local plasticity to learn spatio-temporal patterns in its input while maintaining its dynamics in a healthy regime suitable for learning. The SORN learns to encode information in the form of trajectories through its high-dimensional state space reminiscent of recent biological findings on cortical coding. All three forms of plasticity are shown to be essential for the network's success. Keywords: synaptic plasticity, intrinsic plasticity, recurrent neural networks, reservoir computing, time series prediction Andreea Lazar; Gordon Pipa; Jochen Triesch article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/20110 Tue, 26 Oct 2010 13:29:34 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/7074 Poster presentation: Functional connectivity of the brain describes the network of correlated activities of different brain areas. However, correlation does not imply causality and most synchronization measures do not distinguish causal and non-causal interactions among remote brain areas, i.e. determine the effective connectivity [1]. Identification of causal interactions in brain networks is fundamental to understanding the processing of information. Attempts at unveiling signs of functional or effective connectivity from non-invasive Magneto-/Electroencephalographic (M/EEG) recordings at the sensor level are hampered by volume conduction leading to correlated sensor signals without the presence of effective connectivity. Here, we make use of the transfer entropy (TE) concept to establish effective connectivity. The formalism of TE has been proposed as a rigorous quantification of the information flow among systems in interaction and is a natural generalization of mutual information [2]. In contrast to Granger causality, TE is a non-linear measure and not influenced by volume conduction. ... Michael Wibral; Raul Vicente; Jochen Triesch; Gordon Pipa article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/7074 Sun, 20 Sep 2009 16:26:16 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2744 We present a biologically-inspired system for real-time, feed-forward object recognition in cluttered scenes. Our system utilizes a vocabulary of very sparse features that are shared between and within different object models. To detect objects in a novel scene, these features are located in the image, and each detected feature votes for all objects that are consistent with its presence. Due to the sharing of features between object models our approach is more scalable to large object databases than traditional methods. To demonstrate the utility of this approach, we train our system to recognize any of 50 objects in everyday cluttered scenes with substantial occlusion. Without further optimization we also demonstrate near-perfect recognition on a standard 3-D recognition problem. Our system has an interpretation as a sparsely connected feed-forward neural network, making it a viable model for fast, feed-forward object recognition in the primate visual system. Erik Murphy-Chutorian; Sarah Aboutalib; Jochen Triesch article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/2744 Fri, 12 May 2006 13:43:07 +0200 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3360 Robots of the future should communicate with humans in a natural way. We are especially interested in vision-based gesture interfaces. In the context of robotics several constraints exist, which make the task of gesture recognition particularly challenging. We discuss these constraints and report on progress being made in our lab in the development of techniques for building robust gesture interfaces which can handle these constraints. In an example application, the techniques are shown to be easily combined to build a gesture interface for a real robot grasping objects on a table in front of it. Jochen Triesch; Christoph von der Malsburg article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3360 Mon, 07 Nov 2005 11:48:08 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3376 A computer vision system for non-independent recognition of hand postures against complex background is presented. THe system is based on Elastic Graph Matching (EGM), which was extended to allow for combinations of different feature types at the graph nodes. Jochen Triesch; Christoph von der Malsburg article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3376 Mon, 07 Nov 2005 11:03:05 +0100 http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3377 The binding problem is regarded as one of today's key questions about brain function. Several solutions have been proposed, yet the issue is still controversial. The goal of this article is twofold. Firstly, we propose a new experimental paradigm requiring feature binding, the "delayed binding response task". Secondly, we propose a binding mechanism employing fast reversible synaptic plasticity to express the binding between concepts. We discuss the experimental predictions of our model for the delayed binding response task. Jochen Triesch; Christoph von der Malsburg article http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/3377 Mon, 07 Nov 2005 11:02:48 +0100