Juan A. Sigüenza

Fast Response and Temporal Coherent Oscillations in Small-World Networks

We have investigated the role that different connectivity regimes play in the dynamics of a network of Hodgkin-Huxley neurons by computer simulations. The different connectivity topologies exhibit the following features: random topologies give rise to fast system response yet are unable to produce coherent oscillations in the average activity of the network; on the other hand, regular topologies give rise to coherent oscillations, but in a temporal scale that is not in accordance with fast signal processing. Finally, small-world topologies, which fall between random and regular ones, take advantage of the best features of both, giving rise to fast system response with coherent oscillations.

BiosecurID: a multimodal biometric database

A new multimodal biometric database, acquired in the framework of the BiosecurID project, is presented together with the description of the acquisition setup and protocol. The database includes eight unimodal biometric traits, namely: speech, iris, face (still images, videos of talking faces), handwritten signature and handwritten text (on-line dynamic signals, off-line scanned images), fingerprints (acquired with two different sensors), hand (palmprint, contour-geometry) and keystroking. The database comprises 400 subjects and presents features such as: realistic acquisition scenario, balanced gender and population distributions, availability of information about particular demographic groups (age, gender, handedness), acquisition of replay attacks for speech and keystroking, skilled forgeries for signatures, and compatibility with other existing databases. All these characteristics make it very useful in research and development of unimodal and multimodal biometric systems.

Hill-Climbing and Brute-Force Attacks on Biometric Systems: A Case Study in Match-on-Card Fingerprint Verification

In this paper, we study the robustness of state-of-the-art automatic fingerprint verification systems against hill climbing and brute-force attacks. We compare the performance of this type of attacks against two different minutiae-based systems, the NIST Fingerprint Image Software 2 (NFIS2) reference system and a Match-on-Card based system. In order to study their success rate, the attacks are analyzed and modified in each scenario. We focus on the influence of initial conditions in hill-climbing attacks, like the number of minutiae in the synthetically generated templates or the performance of each type of modification in the template. We demonstrate how slight modifications in the hill-climbing algorithm lead to very different success rates

Relationship between orientation tuning and spatial frequency in neurones of cat area 17

SummaryThe orientation bandwidth was measured at different spatial frequencies for simple and complex cells. With increasing spatial frequency, the orientation tuning of simple cells became progressively narrower. This tendency was much less marked in complex cells. The results are interpreted in support of geniculate cells with orthogonal orientation biases providing the excitatory and inhibitory inputs to a simple cell.

Writer identification method based on forensic knowledge

Police corps have been extensively used Forensic techniques to perform criminal identification. One of these techniques is questioned document examination. Forensic document examiners can identify individuals in big populations using a classification of the forms of manuscript characters, i.e. a handwriting formulation. This paper presents a method that defines a handwriting formulation that allows high identification accuracy minimizing the amount of data used and the sample size. Thus the method improves the query performance in a writing specimens database and it reduces the storage requirements. Experiments with results of 100% accuracy on the identification of 20 criminals in a real forensic database are presented.

Autoassociative neural networks and noise filtering

We introduce linear autoassociative neural (AN) network filters for the removal of additive noise from one-dimensional (1-D) time series. The AN network will have a (2M+1)/spl times/L/spl times/(2M+1) architecture, and for M fixed, we show how to choose the optimal L value and output coordinate from square error estimates between the AN filter outputs and the clean series. The frequency response of AN filters are also studied, and they are shown to act as matched band filters. A noise variance estimate is also derived from this analysis. We numerically illustrate their behavior on two examples and also compare their theoretical performance with that of optimal Wiener filters.

A Central pattern generator to control a pyloric-based system

Abstract. A central pattern generator (CPG) is built to control a mechanical device (plant) inspired by the pyloric chamber of the lobster. Conductance-based models are used to construct the neurons of the CPG. The plant has an associated function that measures the amount of food flowing through it per unit of time. We search for the best set of solutions that give a high positive flow of food in the maximization function. The plant is symmetric and the model neurons are identical to avoid any bias in the space of solutions. We find that the solution is not unique and that three neurons are sufficient to produce positive flow. We propose an effective principle for CPGs (effective on-off connectivity) and a few predictions to be corroborated in the pyloric system of the lobster.

Visual evoked cortical potentials in the cat after retinal modifications induced by intraocular kainic acid

Intraocular injections of kainic acid (KA) induce changes in visual-evoked cortical potentials in the cat at the level of the primary and secondary wave complexes. These changes are correlated with histological findings that show degeneration of cells in the inner nuclear layer and ganglion cell layer. These results indicate that despite the cell death produced by KA, certain retinal circuits continue to function. The fact that the first modifications induced by KA are observed at the level of the primary complex agrees well with the proposed retinal origin of this complex. The modifications of the secondary complex may imply a different transmission and/or processing of visual information at the central level.

Cortical visual evoked potentials during the sleep wakefulness cycle of the freely moving cat. Characterization and statistical comparisons

Visual evoked potentials (VEPs) were obtained during the stages of wakefulness (W), slow sleep (SS) and paradoxical sleep (PS) by means of a light-emitting diode chronically implanted in the frontal sinus of the freely moving cat. Statistical analysis of the variables: latencies, latency intervals and amplitudes, between each of the mentioned stages shows that, for the first components, variations occurred only in the first interval of latency during SS vs. W. Lengthening of VEP latencies and increase of VEP amplitudes were observed for all secondary components in the comparisons between both SS and W, and SS and PS. PS-VEPs vs. W-VEPs showed shortening of latencies and decrease of amplitudes of all secondary components of the former case. The results confirm that in the freely moving cat, the secondary VEP response is more intensely affected by sleep than the primary VEP response, but indicate that there are different mechanisms in the generation of the VEP during SS and PS.

Visually-evoked potentials elicited by a light-emitting diode chronically implanted in the frontal sinus of the freely moving cat

Visually-evoked potentials (VEPs) were obtained with a small yellow light-emitting diode (LED), chronically implanted in the frontal sinus of the cat. The VEPs obtained in scotopic conditions through the LED have a similar morphology to those obtained with a stroboscopic flash. A noticeable delay was observed in LED wave latencies versus flash values. Analysis of wave intervals indicated a long-lasting generation of LED VEPs primary components. Secondary responses have a similar pattern with both modalities of stimulation. Implanted LEDs can be used as a reliable method to obtain VEPs and especially in those behavioural or pathological conditions in which variations exist in the constancy of the ocular media.