Rafael Cabeza

Rafael Cabeza
Public University of Navarre | UPNA · Department of Electric and Electronical Engineering

Full Professor

About

93
Publications
17,531
Reads
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2,345
Citations
Additional affiliations
June 2019 - present
Public University of Navarre
Position
  • Professor (Full)
September 1992 - present
Public University of Navarre

Publications

Publications (93)
Article
Adaptive-weight algorithms currently represent the state of the art in local stereo matching. However, due to their computational requirements, these types of solutions are not suitable for real-time implementation. Here, we present a novel aggregation method inspired by the anisotropic diffusion technique used in image filtering. The proposed aggr...
Article
Full-text available
A viable fully on-line adaptive brain computer interface (BCI) is introduced. On-line experiments with nine naive and able-bodied subjects were carried out using a continuously adaptive BCI system. The data were analyzed and the viability of the system was studied. The BCI was based on motor imagery, the feature extraction was performed with an ada...
Article
The design of robust and high-performance gaze-tracking systems is one of the most important objectives of the eye-tracking community. In general, a subject calibration procedure is needed to learn system parameters and be able to estimate the gaze direction accurately. In this paper, we attempt to determine if subject calibration can be eliminated...
Article
Full-text available
The optimal eating window for time-restricted eating (TRE) remains unclear, particularly its impact on visceral adipose tissue (VAT), which is associated with cardiometabolic morbidity and mortality. We investigated the effects of three TRE schedules (8 h windows in the early day, late day and participant-chosen times) combined with usual care (UC,...
Poster
Evidence suggests that stress levels are rising among children and adolescents in the last years. High levels of stress negatively influence the mental and physical health in youth. Physical activity (PA) levels seem to be inversely related to stress levels. However, evidence supporting the association of physical activity and stress levels is scar...
Article
Context Exercise reduces adiposity, but its influence on bone marrow fat fraction (BMFF) is unknown; nor is it known whether a reduction in liver fat content mediates this reduction. Objectives This work aimed to determine whether incorporating exercise into a lifestyle program reduces the lumbar spine (LS) BMFF and to investigate whether changes...
Article
Purpose: Hepatic steatosis is associated with decreased bone mineral density (BMD). Bone marrow fat fraction (BMFF) could play a role on this relationship in children with obesity. The objectives were: (i) to examine the relationship between the lumbar spine (LS) BMFF and BMD, and (ii) to explore the mediating role of LS-BMFF on the relationship b...
Article
Full-text available
Objectives Fat depots localization has a critical role in the metabolic health status of adults. Nevertheless, whether that is also the case in children remains under‐studied. Therefore, the aims of this study were: (i) to examine the differences between metabolically healthy (MHO) and unhealthy (MUO) overweight/obesity phenotypes on specific abdom...
Article
Full-text available
Importance Excess abdominal fat is a major determinant in the development of insulin resistance and other metabolic disorders. Increased visceral adipose tissue (VAT) seems to precede the development of insulin resistance and is therefore a prime target of childhood lifestyle interventions aimed at preventing diabetes. Objectives To examine the ef...
Article
OBJECTIVE In adults, there is evidence that improvement of metabolic-associated fatty liver disease (MAFLD) depends on the reduction of myosteatosis. In children, in whom the prevalence of MAFLD is alarming, this muscle-liver crosstalk has not been tested. Therefore, we aimed to explore whether the effects of a multicomponent intervention on hepati...
Article
Full-text available
Background The early detection and management of children with metabolic associated fatty liver disease (MAFLD) is challenging. Objective To develop a non‐invasive and accurate prediction protocol for the identification of MAFLD among children with overweight/obesity candidates to confirmatory diagnosis. Methods A total of 115 children aged 8–12...
Article
Full-text available
Objectives To examine the relationship between physical fitness and physical activity (PA) with specific abdominal fat depots and their potential implications for cardiometabolic risk and insulin resistance (IR) in children with overweight/obesity. Materials and Methods A total of 116 children with overweight/obesity (10.7±1.1 yr, 54% girls) parti...
Article
Full-text available
Remote eye tracking technology has suffered an increasing growth in recent years due to its applicability in many research areas. In this paper, a video-oculography method based on convolutional neural networks (CNNs) for pupil center detection over webcam images is proposed. As the first contribution of this work and in order to train the model, a...
Article
Full-text available
Subject calibration has been demonstrated to improve the accuracy in high-performance eye trackers. However, the true weight of calibration in off-the-shelf eye tracking solutions is still not addressed. In this work, a theoretical framework to measure the effects of calibration in deep learning-based gaze estimation is proposed for low-resolution...
Chapter
In this paper, we focus on the calibration possibilitiesó of a deep learning based gaze estimation process applying transfer learning, comparing its performance when using a general dataset versus when using a gaze specific dataset in the pretrained model. Subject calibration has demonstrated to improve gaze accuracy in high performance eye tracker...
Preprint
Full-text available
In this paper, we evaluate a synthetic framework to be used in the field of gaze estimation employing deep learning techniques. The lack of sufficient annotated data could be overcome by the utilization of a synthetic evaluation framework as far as it resembles the behavior of a real scenario. In this work, we use U2Eyes synthetic environment emplo...
Article
Eye tracking technology in low resolution scenarios is not a completely solved issue to date. The possibility of using eye tracking in a mobile gadget is a challenging objective that would permit to spread this technology to non-explored fields. In this paper, a knowledge based approach is presented to solve gaze estimation in low resolution settin...
Article
Currently, consumers display what is known as omnichannel behavior: the combined use of digital and physical channels providing them with multiple points of contact with firms. We combine the stimulus-organism-response (S-O-R) model and visual attention theory to study how customers’ attention to digital channels varies across different purchasing...
Conference Paper
Availability of large scale tagged datasets is a must in the field of deep learning applied to the eye tracking challenge. In this paper, the potential of Supervised-Descent-Method (SDM) as a semiautomatic labelling tool for eye tracking images is shown. The objective of the paper is to evidence how the human effort needed for manually labelling la...
Article
Full-text available
Head pose estimation (HPE) is currently a growing research field, mainly because of the proliferation of human–computer interfaces (HCI) in the last decade. It offers a wide variety of applications, including human behavior analysis, driver assistance systems or gaze estimation systems. This article aims to contribute to the development of robust a...
Article
Full-text available
In head-mounted eye tracking systems, the correct detection of pupil position is a key factor in estimating gaze direction. However, this is a challenging issue when the videos are recorded in real-world conditions, due to the many sources of noise and artifacts that exist in these scenarios, such as rapid changes in illumination, reflections, occl...
Conference Paper
I2Head database has been created with the aim to become an optimal reference for low cost gaze estimation. It exhibits the following outstanding characteristics: it takes into account key aspects of low resolution eye tracking technology; it combines images of users gazing at different grids of points from alternative positions with registers of us...
Conference Paper
The precise detection of pupil/iris center is key to estimate gaze accurately. This fact becomes specially challenging in low cost frameworks in which the algorithms employed for high performance systems fail. In the last years an outstanding effort has been made in order to apply training-based methods to low resolution images. In this paper, Supe...
Article
A new public database of videos for head tracking and pose estimation is presented in this paper with the goal of establishing a new framework for algorithm validation, replacing out of date frameworks. Position data has been recorded with a magnetic sensor-transmitter that has previously been aligned and synchronized with a commercial webcam, and...
Article
The discrimination between benign and malignant adnexal masses in ultrasound images represents one of the most challenging problems in gynecologic practice. In the study described here, a new method for automatic discrimination of adnexal masses based on a neural networks approach was tested. The proposed method first calculates seven different typ...
Conference Paper
Full-text available
Point Distribution Models (PDM) are some of the most popular shape description techniques in medical imaging. However, to create an accurate shape model it is essential to have a representative sample of the underlying population, which is often challenging. This problem is particularly relevant as the dimensionality of the modeled structures incre...
Article
Full-text available
Accurate detection of iris center and eye corners appears to be a promising approach for low cost gaze estimation. In this paper we propose novel eye inner corner detection methods. Appearance and feature based segmentation approaches are suggested. All these methods are exhaustively tested on a realistic dataset containing images of subjects gazin...
Conference Paper
One of the goals of the eye tracking community is to build systems that allow users to move freely. In general, there is a trade-off between the field of view of an eye tracking system and the gaze estimation accuracy. We aim to study how much the field of view of an eye tracking system can be increased, while maintaining acceptable accuracy. In th...
Article
Active shape models (ASMs) are some of the most actively used model-based segmentation approaches, whose usefulness has been successfully demonstrated in a wide variety of applications. However, they suffer from two important drawbacks: (1) the large number of training samples required to adequately model the object of interest and (2) their depend...
Conference Paper
Full-text available
Point distribution models (PDM) are one of the most extended methods to characterize the underlying population of set of samples, whose usefulness has been demonstrated in a wide variety of applications, including medical imaging. However, one important issue remains unsolved: the large number of training samples required. This problem becomes crit...
Article
A multistage procedure to detect eye features is presented. Multiresolution and topographic classification are used to detect the iris center. The eye corner is calculated combining valley detection and eyelid curve extraction. The algorithm is tested in the BioID database and in a proprietary database containing more than 1200 images. The results...
Article
The incorporation of a multiresolution image approach is one of the most popular variants of Active Shape Models (ASMs), providing a more robust algorithm and minimizing its initialization dependency. Using the wavelet transform, the present paper extends the multiresolution analysis to the shape space, developing a novel multiresolution shape fram...
Conference Paper
Being able to perform eye tracking with low cost technology is the key to broaden its applications and one of the major goals for the eye tracking community nowadays. Furthermore, new datasets to evaluate the different methods are needed to reproduce the real conditions in which these algorithms work. In this paper, we present a dataset containing...
Conference Paper
When performing eye detection in a driving scenario, new challenges arise that do not occur in a standard indoor eye tracking session. Rapid subject movement, non-controlled fast light variation and partial or total occlusions are the main problems that must be overcome. Furthermore, sunlight's infrared component makes it difficult the use of activ...
Article
Gaze-tracking data have been used successfully in the design of new input devices and as an observational technique in usability studies. Polynomial-based Video-Oculography (VOG) systems are one of the most attractive gaze estimation methods thanks to their simplicity and ease of implementation. Although the functionality of these systems is genera...
Article
Video oculography (VOG) is one of the most commonly used techniques for gaze tracking because it enables nonintrusive eye detection and tracking. Improving the eye tracking's accuracy and tolerance to user head movements is a common task in the field of gaze tracking; thus, a thorough study of how binocular information can improve a gaze tracking s...
Article
Full-text available
Active Shape Models (ASMs) have become one of the most widespread segmentation paradigms since their inception in the early nineties. However, their capability to capture and model the shapes' variability is highly conditioned by the training set used. Trying to overcome this limitation, this paper presents a new hierarchical for-mulation of classi...
Article
The development of systems that track the eye while allowing head movement is one of the most challenging objectives of gaze tracking researchers. Tracker accuracy decreases as the subject moves from the calibration position and is especially influenced by changes in depth with respect to the screen. In this paper, we demonstrate that the pattern o...
Article
Low cost eye tracking is an actual challenging research topic for the eye tracking community. Gaze tracking based on a web cam and without infrared light is a searched goal to broaden the applications of eye tracking systems. Web cam based eye tracking results in new challenges to solve such as a wider field of view and a lower image quality. In ad...
Article
Full-text available
The accurate segmentation of subcortical brain structures in magnetic resonance (MR) images is of crucial importance in the interdisciplinary field of medical imaging. Although statistical approaches such as active shape models (ASMs) have proven to be particularly useful in the modeling of multiobject shapes, they are inefficient when facing chall...
Conference Paper
Full-text available
Local stereo matching algorithms based on adapting-weights aggregation produce excellent results compared to other local methods. In particular, they produce more accurate results near disparity edges. This improvement is obtained thanks to the fact that the support for each pixel is accurately determined based on information such as colour or spat...
Conference Paper
Full-text available
Recent local stereo matching algorithms based on an adaptive-weight strategy achieve accuracy similar to global approaches. One of the major problems of these algorithms is that they are computationally expensive and this complexity increases proportionally to the window size. This paper proposes a novel cost aggregation step with complexity indepe...
Article
Due to the similarities between neighbouring pixels as well as the intensity-value differences between corresponding pixels, classical matching measures based on intensity similarity produce slightly imprecise results. In this study, a gradient similarity-matching measure was implemented in a state-of-the-art local stereo-matching method (an adapti...
Conference Paper
Low cost iris tracking is one of the most challenging research topics for the eye-tracking community. To this end, accurate detection of the iris centre in images captured by a web cam is a major goal. We propose a novel method for iris detection that is based on image topography using multi-resolution to detect the most stable "valley" over differ...
Conference Paper
Full-text available
— Local stereo matching algorithms based on the adapting-weights strategy achieve accuracy similar to global approaches. One of the major problems of these local algorithms is that they are computationally expensive. However, algorithms with reduced computational complexity inspired by the adapting-weights strategy have been recently proposed. In p...
Article
Full-text available
A new system is presented that enhances the interoperability between a video-oculographic (VOG) system for mouse movement control and an electromyographic (EMG) system for mouse click detection. The proposed VOG-EMG system combines gaze and muscle information to minimize the number of undesired clicks due to involuntary activations and environmenta...
Article
Full-text available
Active Shape Models are some of the most actively researched model-based seg-mentation approaches. An accurate estimation of the shape probability distribution is essential to provide the prior knowledge that makes ASMs able to handle the large in-herent variability of anatomical structures, differentiating between allowed and invalid instances. Un...
Article
The main objective of gaze trackers is to provide an accurate estimate of the user's gaze by using the eye tracking information. Gaze, in its most general form, can be considered to be the line of sight or line of gaze, as 3D (imaginary) lines with respect to the camera, or as the point of regard (also termed the point of gaze). This chapter introd...
Article
In this paper we present a new fullautomatic glottis segmentation scheme that combines traditional bottom-up image processing techniques with high-level shape constraints provided by the active shape Models. unlike previous statistical segmentation approaches, which try to accurately detect the location of the glottis as initialization for the algo...
Article
This paper presents a principled analysis of various combinations of image features to determine their suitability for remote eye tracking. It begins by reviewing the basic theory underlying the connection between eye image and gaze direction. Then a set of approaches is proposed based on different combinations of well-known features and their beha...
Article
The complexity of corneal refraction modeling complicates geometrical analysis of gaze tracking systems. The task can be accomplished in different ways by means of different approximations. Depending on the assumptions made, errors can arise and the accuracy of trackers can end up determined to an excessive degree by the hardware setup and subject...
Article
Full-text available
A number of functional systems are involved in the control of eye movements. The vestibulo-ocular and optokinetic reflexes are automatic responses that compensate for the movements of the head and those of the visual environment in order to stabilize the retinal image on a given fixation point. The saccadic movements are quick displacements of fixa...
Article
En el control de la motilidad ocular intervienen varios sistemas funcionales. Los reflejos vestíbulo-oculares y optocinéticos son respuestas automáticas para compensar los movimientos de la cabeza y del entorno visual y poder estabilizar la imagen retiniana sobre un determinado punto de fijación. Los movimientos sacádicos son rápidos desplazamiento...
Chapter
Full-text available
A geometry-based model for gaze estimation has been constructed and evaluated. Alternative models have been proposed based on different image features. The results show that a hybrid model is needed for LoS estimation in a free head pose scenario, since glints and pupil separately do not provide sufficient information for optical axis estimation. G...
Conference Paper
Of gaze tracking techniques, video-oculography (VOG) is one of the most attractive because of its versatility and simplicity. VOG systems based on general purpose mapping methods use simple polynomial expressions to estimate a user's point of regard. Although the behaviour of such systems is generally acceptable, a detailed study of the calibration...
Article
An innovative way of teaching introductory circuit theory to higher education first courses of non-electrical engineering students arises from our own teaching experience. In these students' learning programme, circuit theory is located at the very early stages (first or second semester, when the student is still not too skilled on maths). Fewer cr...
Article
Full-text available
One of the most confusing aspects that one meets when introducing oneself into gaze tracking technology is the wide variety, in terms of hardware equipment, of available systems that provide solutions to the same matter, that is, determining the point the subject is looking at. The calibration process permits generally adjusting nonintrusive tracke...
Article
In the past years, research in eye tracking development and applications has attracted much attention and the possibility of interacting with a computer employing just gaze information is becoming more and more feasible. Efforts in eye tracking cover a broad spectrum of fields, system mathematical modeling being an important aspect in this research...
Conference Paper
One of the most confusing aspects that one meets as he introduces himself into gaze tracking is the variety, in terms of hardware equipment, of available systems providing solutions to the same matter, i.e. determining subject’s gaze. Calibration permits adjusting trackers based on different hardware and image features to the subject. The negative...
Chapter
The latest research in the development of technologies that will allow humans to communicate, using brain signals only, with computers, wheelchairs, prostheses, and other devices. Interest in developing an effective communication interface connecting the human brain and a computer has grown rapidly over the past decade. The brain-computer interface...
Article
Full-text available
A study of different on-line adaptive classifiers, using various feature types is presented. Motor imagery brain computer interface (BCI) experiments were carried out with 18 naive able-bodied subjects. Experiments were done with three two-class, cue-based, electroencephalogram (EEG)-based systems. Two continuously adaptive classifiers were tested:...
Article
We present a study of linear, quadratic and regularized discriminant analysis (RDA) applied to motor imagery data of three subjects. The aim of the work was to find out which classifier can separate better these two-class motor imagery data: linear, quadratic or some function in between the linear and quadratic solutions. Discriminant analysis meth...
Article
Full-text available
One major challenge in Brain-Computer Interface (BCI) research is to cope with the inherent nonstationarity of the recorded brain signals caused by changes in the subjects brain processes during an experiment. Online adaptation of the classifier embedded into the BCI is a possible way of tackling this issue. In this chapter we investigate the effec...
Article
Lately eye tracking system development and applications are becoming increasingly interesting. Efforts in eye tracking research cover a broad spectrum of fields, being mathematical modeling an important aspect and probably one of the least explored topics. In order to build up a robust and efficient model a deep mathematical review of the geometry...
Conference Paper
Full-text available
Pupil detection represents one of the most critical aspects for eye tracking systems based on video oculography. A robust segmentation of the aforementioned feature determines to a large extent the degree of performance of the system. However, a question remains unsolved... why does the pupil gray level change in the image? Apart from the possible...
Article
We present the result of on-line feedback Brain Computer Interface experiments using adaptive and non-adaptive feature extraction methods with an on-line adaptive classifier based on Quadratic Discriminant Analysis. Experiments were performed with 12 naïve subjects, feedback was provided from the first moment and no training sessions were needed. E...
Conference Paper
Full-text available
This work presents a robust real time algorithm for an eye tracking system employing the well-known bright-pupil technique that performs an effective detection of the pupil and glint positions in the image. The accuracy in the processing is essential if a good determination of the eye gaze is desired. This algorithm is competent for unconstrained i...
Conference Paper
Full-text available
Calibration is one of the most tedious and often annoying aspects of many eye tracking systems. It normally consists in looking at several marks on a screen in order to collect enough data to modify the parameters of an adjustable model. Unfortunately this step is unavoidable if a competent tracking system is desired. Many efforts have been made to...
Article
Full-text available
In this paper several examples of circuits obtained with an automatic synthesis algorithm will be shown. The algorithm, described in a companion paper [1] and outlined here for clarity, has been implemented in the Mathematica \bigcirc \textTM \begin{gathered} \bigcirc \hfill \\ {\kern 1pt} ^{{\text{TM}}} \hfill \\ \end{gathered} language. We appl...
Article
The eyes can come to be the sole tool of communication for highly disabled patients. With the appropriate technology it is possible to successfully interpret eye movements, increasing the possibilities of patient communication with the use of speech synthesisers. A system of these characteristics will have to include a speech synthesiser, an interf...
Article
An algorithm for the synthesis of immittances is briefly described. Given a driving point immittance function and specifying the number of nodes, the algorithm will generate all the networks fulfilling the specified function with the predetermined number of nodes. This algorithm has been implemented with MathematicaTM in a desktop workstation with...