5638 3 TV Wiecki K Riedinger A Ameln-Mayerhofer WJ Schmidt MJ Frank 2009-01-00 2 204 265 277 Psychopharmacology Rationale Repeated haloperidol treatment in rodents results in a day-to-day intensification of catalepsy (i.e., sensitization). Prior experiments suggest that this sensitization is context-dependent and resistant to extinction training. Objectives The aim of this study was to provide a neurobiological mechanistic explanation for these findings. Materials and methods We use a neurocomputational model of the basal ganglia and simulate two alternative models based on the reward prediction error and novelty hypotheses of dopamine function. We also conducted a behavioral rat experiment to adjudicate between these models. Twenty male Sprague–Dawley rats were challenged with 0.25 mg/kg haloperidol across multiple days and were subsequently tested in either a familiar or novel context. Results Simulation results show that catalepsy sensitization, and its context dependency, can be explained by “NoGo” learning via simulated D2 receptor antagonism in striatopallidal neurons, leading to increasingly slowed response latencies. The model further exhibits a non-extinguishable component of catalepsy sensitization due to latent NoGo representations that are prevented from being expressed, and therefore from being unlearned, during extinction. In the rat experiment, context dependency effects were not dependent on the novelty of the context, ruling out the novelty model’s account of context dependency. Conclusions Simulations lend insight into potential complex mechanisms leading to context-dependent catalepsy sensitization, extinction, and renewal. no notspecified http://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/Psychopharmacology-Wiecki-preprint_[0].pdf published 12 15017 18823 5018 3 K Drewing TV Wiecki MO Ernst 2008-06-00 2 128 264 273 Acta Psychologica When integrating estimates from redundant sensory signals, humans seem to weight these estimates according to their reliabilities. In the present study, human observers used active touch to judge the curvature of a shape. The curvature was specified by positional and force signals: When a finger slides across a surface, the finger’s position follows the surface geometry (position signal). At the same time it is exposed to patterns of forces depending on the gradient of the surface (force signal; Robles-de-la Torre & Hayward, 2001). We show that variations in the surface’s material properties (compliance, friction) influence the sensorily available position and force signals, as well as the the noise associated with these signals. Along with this, material properties affect the weights given to the position and force signals for curvature judgements. Our findings are consistent with the notion of an observer who weights signal estimates according to their reliabilities. That is, signal wei ghts shifted with the signal noise, which in the present case resulted from active exploration. no notspecified http://www.kyb.tuebingen.mpg.de/ published 9 15017 18824 4304 7 M Bethge TV Wiecki FA Wichmann San Jose, CA, USA2007-02-00 1 12 SPIE Human Vision and Electronic Imaging Conference 2007 The independent components of natural images are a set of linear filters which are optimized for statistical independence. With such a set of filters images can be represented without loss of information. Intriguingly, the filter shapes are localized, oriented, and bandpass, resembling important properties of V1 simple cell receptive fields. Here we address the question of whether the independent components of natural images are also perceptually less dependent than other image components. We compared the pixel basis, the ICA basis and the discrete cosine basis by asking subjects to interactively predict missing pixels (for the pixel basis) or to predict the coefficients of ICA and DCT basis functions in patches of natural images. Like Kersten (1987) we find the pixel basis to be perceptually highly redundant but perhaps surprisingly, the ICA basis showed significantly higher perceptual dependencies than the DCT basis. This shows a dissociation between statistical and perceptual dependence measures. no notspecified http://www.kyb.tuebingen.mpg.de//fileadmin/user_upload/files/publications/EI105-IndependentComponents_4304[0].pdf published 11 15017 1542015017 18823 3784 7 K Drewing MO Ernst T Wiecki Pisa, Italy2005-03-00 1 6 1st Joint Worldhaptic Conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems (WorldHaptics 2005) When sliding a finger across a bumpy surface, the finger follows the surface geometry (position signal). At the same time the finger is exposed to forces related to the slope of the surface (force signal) [1]. For haptic shape perception the brain uses both signals integrating them by weighted averaging [2]. This is consistent with the Maximum-Likelihood-Estimate (MLE) model on signal integration, previously only applied to passive perception. The model further predicts that signal weight is proportional to signal reliability. Here, we tested this prediction for the integration of force and position signals to perceived curvature by manipulating material properties of the curve. Low as compared to high compliance decreased the reliability and so the weight of the sensorily transduced position signal. High as compared to low friction decreased the reliability and so the weight of the transduced force signal. These results demonstrat that the MLE model extends to situations involving active touch. no notspecified http://www.kyb.tuebingen.mpg.de/fileadmin/user_upload/files/publications/WHC-2005-Drewing.pdf published 5 15017 1542215017 18824 2515 7 K Drewing T Wiecki MO Ernst Tübingen, Germany2004-02-00 123 7th Tübingen Perception Conference (TWK 2004) When sliding a nger across a bumpy surface, the nger follows the geometry of the bumps/holes providing positional cues for the shape. At the same time the nger is opposed by forces related to the steepness of the bumps/holes. With a specic device Robles-de-la-Torre and Hayward [1] dissociated positional and force cues in the haptic perception of small-scale bumps and holes: Participants in this experiment reported to predominantly feel the class of shapes (bumps or holes) indicated by the force cues. Drewing and Ernst [2] extended this research by disentangling force and position cues to the perception of curves more systematically and by also quantifying the perceived curvature. The result was that the perceived curvature could be predicted from weighted averaging of the two cues. This is consistent with current models of cue integration [e.g., 3]. These integration models further predict that the cue weight is proportional to the cue's reliability. Here, we aimed at testing this prediction for the integration of force and position cues to haptic shape by manipulating the shapes' material properties: high softness can be assumed to decrease the reliability of the position cue as compared to low softness, and high friction to decrease the reliability of the force cue. Using the PHANToM force-feedback device we constructed haptic curve stimuli. We systematically intermixed force and position cues indicating curvatures of 14 and 24 /m. Using the method of double-staircases, we measured the point of subjective equality (PSE) of the curvature of these as compared to `natural' stimuli (i.e., with consistent position and force cues). From the PSE data we determined the cue weights. This was done under each combination of material properties (low vs high softness X low vs high friction). We found that material properties affected the cue weights in a manner consistent with our predictions. These results further conrm the validity of existing models of cue integration in haptic shape perception. no notspecified http://www.kyb.tuebingen.mpg.de/ published -123 15017 1542215017 18824