Rodrigo Ventura - Academia.edu (original) (raw)

Papers by Rodrigo Ventura

The synchronization of dynamical systems is a method that allows two systems to have identical st... more The synchronization of dynamical systems is a method that allows two systems to have identical state trajectories, appart from an error converging to zero. This method consists in an appropriate unidirectional coupling from one system (drive) to the other (response). This requires that the response system shares the same dynamical model with the drive. For the cases where the drive is unknown, Chen proposed in 2002 a method to adapt the response system such that synchronization is achieved, provided that (1) the response dynamical model is linear with a vector of parameters, and (2) there is a parameter vector that makes both system dynamics identical. However, this method has two limitations: first, it does not scale well for complex parametric models (e.g., if the number of parameters is greater than the state dimension), and second, the model parameters are not guaranteed to converge, namely as the synchronization error approaches zero. This paper presents an adaptation law addressing these two limitations. Stability and convergence proofs, using Lyapunov's second method, support the proposed adaptation law. Finally, numerical simulations illustrate the advantages of the proposed method, namely showing cases where the Chen's method fail, while the proposed one does not.

Computing Research Repository, 2010

Most cognitive architectures rely on discrete representation, both in space (e.g., objects) and i... more Most cognitive architectures rely on discrete representation, both in space (e.g., objects) and in time (e.g., events). However, a robot interaction with the world is inherently continuous, both in space and in time. The segmentation of the stream of perceptual inputs a robot receives into discrete and meaningful events poses as a challenge in bridging the gap between internal cognitive representations, and the external world. Event Segmentation Theory, recently proposed in the context of cognitive systems research, sustains that humans segment time into events based on matching perceptual input with predictions. In this work we propose a framework for online event segmentation, targeting robots endowed with active perception. Moreover, sensory processing systems have an intrinsic latency, resulting from many factors such as sampling rate, and computational processing, and which is seldom accounted for. This framework is founded on the theory of dynamical systems synchronization, where the system considered includes both the robot and the world coupled (strong anticipation). An adaption rule is used to perform simultaneous system identi?cation and synchronization, and anticipating synchronization is employed to predict the short-term system evolution. This prediction allows for an appropriate control of the robot actuation. Event boundaries are detected once synchronization is lost (sudden increase of the prediction error). An experimental proof of concept of the proposed framework is presented, together with some preliminary results corroborating the approach.

According to Damasio (Damasio 1994), some aspects of human intelligence, namely the ability to ma... more According to Damasio (Damasio 1994), some aspects of human intelligence, namely the ability to make appropriate decisions in dynamic, complex, and un-predictable environments, depend on emotions. This paper follows previous theoretical work (Ventura & Pinto-Ferreira ...

In this paper, an architecture for an emotion-based agent and its application to a real robot, si... more In this paper, an architecture for an emotion-based agent and its application to a real robot, situated in a semistructured environment, is presented. This architecture corresponds to an improved version of the one proposed by Maqas et. al.. Both were developed based on a particular interpretation of the neuro-physiological findings of Dam~isio and LeDoux, namely the concepts of stimuli parallel processing, by LeDoux, and somatic marking, by Dam~isio. Given several applications of this architecture with virtual agents and in simulated environments, the goal here was to study and evaluate the utility and efficiency of this emotion-based agent architecture with real robots and real environments.

Abstract: The question of implementing emotions in robots is twofold: on the on hand it should be... more Abstract: The question of implementing emotions in robots is twofold: on the on hand it should be verified whether such an effort is valuable, and on the other it should be determined whether the implementation is feasible. The answer to the first question seems ...

Establishing cause-effect relationships is a relevant problem in A.I., particularly for providing... more Establishing cause-effect relationships is a relevant problem in A.I., particularly for providing autonomous agents with models (for decision making) obtained from their interaction with the environment. The strategy adopted in this paper consists of formulating a predictive model of the relevant consequences of agent actions (or inactions). From the agent perspective, a stimulus is relevant whenever either it is desirable (or undesirable), or when the occurrence of that particular stimulus contributes to the anticipation of desirable (or undesirable) stimuli. The purpose of the agent is to use the formulated causal model to act upon on the environment, in order to avoid undesirable stimuli. To validate the approach, the agent was exposed to a very simple environment. Preliminary results are presented, showing that this approach is worth pursuing.

The relevance of the model presented to the control and the supervision of systems lies in the fa... more The relevance of the model presented to the control and the supervision of systems lies in the fact that, in this context, it is very important to respond quickly and efficiently to unexpected situations, by learning associations between current situations and control strategies. The inputs and the state variables of a system can be considered as stimuli to feed a double processing system. The cognitive image can be considered as the set of values collected in a time frame. On the other hand, the perceptual image can result from the determination of certain characteristics such as overshoot, rate of variation of state variables, and so on. The next step is to establish a basic set of associations in order to allow the system to respond to urgent situations (solely based on the perceptual image). As the supervisor starts marking cognitive images with perceptual ones (a basic mechanism of learning), it becomes able to anticipate those situations (this is what humans apparently do when using the somatic marker). On the other hand, the matching of a certain configuration with one previously stored in memory can be assessed in terms of the positiveness or negativeness of the present situation by consulting the cognitive/perceptual mark. The control and supervision of large scale, non-linear, and non time-invariant systems ought to incorporate planning and decision making mechanisms together with low-level controllers, integrated in such a way that performance (both in terms of learning, quality of response, and efficiency) is ensured

The research presented here follows a biologically inspired approach, based on the hypothesis tha... more The research presented here follows a biologically inspired approach, based on the hypothesis that emotions contribute decisively for humans to cope with complex and dynamic environments. This hypothesis is founded on neurophysiological findings showing that damage in the emotion circuitry of the brain cause inability to handle simple, common life tasks . Inspired by these findings, an emotion-based agent model was previously presented [2], proposing a doubleprocessing of stimuli: a simple representation termed perceptual image, designed for fast processing and immediate response to urgent situations, and a complex representation termed cognitive image, thus slow to process, are extracted from each stimulus reaching the agent. These two representations are extracted and processed, simultaneously, by the two levels of the architecture: the perceptual and the cognitive levels. The parallelism of the processing is essential, so that quick response to urgent situations is not compromised by the slow processing of the cognitive level. These two representations are then associated and stored in memory. Once the agent faces a new situation, it matches the incoming stimulus with the agent memory, thus retrieving the associated images.

Neurocomputing, 2009

It is widely accepted that one important role of emotions consists in providing a mechanism for a... more It is widely accepted that one important role of emotions consists in providing a mechanism for adequate and efficient response to relevant stimuli. In this paper we propose a methodology for implementing such a mechanism, based on a previously presented emotion-based agent model. This agent model is biologically inspired in the emotion mechanisms found in the brain, following recent neurophysiological research. This model is founded on two principles: (1) stimuli is represented internally by two representations with different degrees of complexity and accuracy, and (2) the matching of these representations is implemented by a distance function. The mechanism considered in this paper amounts to matching the current stimulus the agent is perceiving with its past experience. This paper addresses a twofold strategy for optimizing the efficiency and accuracy of this mechanism. The first one consists in adapting the distance function employed in one of the representations, while the second one has the goal of upgrading that representation with new relevant features. Techniques borrowed from nonmetric multidimensional scaling are used to approach these goals.

The DARE architecture is an emotion-based agent model. This model is based on a double-representa... more The DARE architecture is an emotion-based agent model. This model is based on a double-representation of stimuli: a complex representation, oriented towards recognition, and simple one, oriented towards feature extraction. These two representations are associated and stored in the agent memory. This paper describes a formalization of an indexing mechanism. Given a new stimulus, the goal of this mechanism consists of finding in memory, efficiently, using the simple representation, the best matching item according to the complex representation. To assess the efficiency gain of this mechanism, an implementation was devised using the classic recognition problem of handwritten digits.

In this paper we present and discuss a conceptual framework to design and construct emotion-based... more In this paper we present and discuss a conceptual framework to design and construct emotion-based agents. We hypothesize that these agents exhibit a sensori-motor intelligence capable of providing them competence to cope with real, aggressive, and unpredictable environments. We sustain that such intelligence -based on a structured pictoric knowledge representation -can bridge the gap between purely reactive agents and complex, logic based, reasoning systems.

This paper presents a receptionist robot that is currently being developed at the Institute for S... more This paper presents a receptionist robot that is currently being developed at the Institute for Systems and Robotics (ISR) -Lisbon, focusing the presentation on the people detection and tracking algorithm. The followed methodology focuses on the integration of several modules, such as navigation, human-robot interaction, and people detection, in order to achieve an autonomous system. In order to save time and effort, as well as obtaining a robust solution, "off-the-shelf" software packages are being used whenever possible. However, for the people detection and tracking algorithms, it was necessary to develop a solution from scratch, using the robot's omnidirectional vision system. 1

This paper proposes an alternative approach to common teleoperation methods found in search and r... more This paper proposes an alternative approach to common teleoperation methods found in search and rescue (SAR) robots. Using a head mounted display (HMD) the operator is capable of perceiving rectified images of the robot world in 3-D, as transmitted by a pair of stereo cameras onboard the robot. The HMD is also equipped with an integrated head-tracker, which permits controlling the robot motion in such a way that the cameras follow the operator's head movements, thus providing an immersive sensation to him. We claim that this approach is a more intuitive and less error prone teleoperation of the robot. The proposed system was evaluated by a group of subjects, and the results suggest that it may yield significant benefits to the effectiveness of the SAR mission. In particular, the user's depth perception and situational awareness improved significantly when using the HMD, and their performance during a simulated SAR operation was also enhanced, both in terms of operation time and on successful identification of objects of interest.

This work describes a semi-autonomous robot for rescue operations, nicknamed RAPOSA (FOX in Engli... more This work describes a semi-autonomous robot for rescue operations, nicknamed RAPOSA (FOX in English). The robot was designed and built to operate in outdoor environments hostile to the human presence, such as debris resulting from the collapse of built structures, and is targeted to the tele-operated detection of potential survivors using a set of speci c sensors whose information is transmitted to a remote human operator. RAPOSA's mechanical structure is composed of a main body and a front body, whose locomotion is supported on tracked wheels, allowing motion even when the robot is upside down. The front body has variable tilting capabilities, providing means to overcome edges higher than the robot main body (e.g., when climbing a stair) and is also useful to grab the lower ground when only the main body has ground contact. This front body has one thermal camera and two webcameras installed. Additional sensors include gas, temperature and humidity sensors, web cams, light diodes, microphone and loudspeaker. The robot uses wireless communications, with an option for tethered operation. The tether carries both power and communications, with an access point on its end, and can also be used to suspend the robot inside a deep hole. Docking and undocking the robot to the tether is accomplished remotely by the operator with the help of a camera located inside the robot, and represents the most innovative feature of RAPOSA.

Industrial Robot-an International Journal, 2007

Purpose -To describe a robot designed and built to operate in outdoor environments hostile to the... more Purpose -To describe a robot designed and built to operate in outdoor environments hostile to the human presence, such as debris resulting from the collapse of built structures, and targeted to the tele-operated detection of potential survivors using a set of specific sensors whose information is transmitted to a remote human operator. Design/methodology/approach -RAPOSA's mechanical structure is composed of a main body and a front body, whose locomotion is supported on tracked wheels, allowing motion even when the robot is upside down. The front body has variable tilting capabilities, providing means to overcome edges higher than the robot main body (e.g. when climbing a stair) and is also useful to grab the lower ground when only the main body has ground contact. This front body has one thermal camera and two webcameras installed. Additional sensors include gas, temperature and humidity sensors, web cams, light diodes, microphone and loudspeaker. The robot uses wireless communications, with an option for tethered operation.

IEEE Transactions on Biomedical Engineering, 2010

Karyotyping is a set of procedures, in the scope of the cytogenetics, that produces a visual repr... more Karyotyping is a set of procedures, in the scope of the cytogenetics, that produces a visual representation of the 46 chromosomes observed during the metaphase step of the cellular division, called mitosis, paired and arranged in decreasing order of size. Automatic pairing of bone marrow cells is a difficult task because these chromosomes appear distorted, overlapped, and their images are usually blurred with undefined edges and low level of detail. In this paper, a new metric is proposed to compare this type of chromosome images toward the design of an automatic pairing algorithm for leukemia diagnostic purposes. Besides the features used in the traditional karyotyping procedures, a new feature, based on mutual information, is proposed to increase the discriminate power of the G-banding pattern dissimilarity between chromosomes and improve the performance of the classifier. The pairing algorithm is formulated as a combinatorial optimization problem where the distances between homologous chromosomes are minimized and the distances between nonhomologous ones are maximized. The optimization task is solved by using an integer programming approach. A new bone marrow chromosome dataset-Lisbon-K1 (LK1) chromosome dataset with 9200 chromosomeswas build for this study. These chromosomes have much lower quality than the classic Copenhagen, Edinburgh, and Philadelphia datasets, and its classification and pairing is therefore more difficult. Experiments using real images from the LK 1 and Grisan et al. datasets based on a leave-one-out cross-validation strategy are performed to test and validate the pairing algorithm.

Cytogenetics is a key tool in the detection of acquired chromosomal abnormalities and in the diag... more Cytogenetics is a key tool in the detection of acquired chromosomal abnormalities and in the diagnosis of genetic diseases such as leukemia. The karyotyping is a set of procedures, in the scope of the cytogenetics, that produces a visual representation of the 46 chromosomes (called karyogram), paired and arranged in decreasing order of size.

Cytogenetics is the preferred tool in the diagnosis of genetic diseases such as leukemia and dete... more Cytogenetics is the preferred tool in the diagnosis of genetic diseases such as leukemia and detection of aquired chromosomal abnormalities, such as translocations, deletions, monosomies or trisomies, etc. The karyotyping is a set of procedures, in the scope of the cytogenetics, that produces a visual representation of the 46 chromosomes, paired and arranged in decreasing order of size, observed during the metaphase step of the cellular division (meiosis).

Computing Research Repository, 2010

Neurocomputing, 2009

Industrial Robot-an International Journal, 2007

IEEE Transactions on Biomedical Engineering, 2010