Murielle Kirkove

Comparative evaluation of existing and new methods for correcting ocular artifacts in electroencephalographic recordings

EEG signals are often contaminated by ocular artifacts (OAs), in particular when they are recorded for a subject that is, in principle, awake, such as in a study of drowsiness. It is generally desirable to detect and/or correct these OAs before interpreting the EEG signals. We have identified 11 existing methods for dealing with OAs. Their study allowed us to create 16 new methods. We performed a comparative performance evaluation of the resulting 27 distinct methods using a common set of data and a common set of metrics. The data was recorded during a driving task of about two hours in a driving simulator. This led to a ranking of all methods, with five emerging clear winners, comprising two existing methods and three new ones.

EVALUATION OF THE PERFORMANCE OF AN EXPERIMENTAL SOMNOLENCE QUANTIFICATION SYSTEM IN TERMS OF REACTION TIMES AND LAPSES

Somnolence is known to be a major cause of various types of accidents, and ocular parameters are recognized to be reliable physiological indicators of somnolence. We have thus developed an experimental somnolence quantification system that uses images of the eye and that produces a level of somnolence on a continuous numerical scale. The aim of this paper is to show that the level of somnolence produced by our system is well related to the level of performance of subjects accomplishing three reaction-time tests in different sleep conditions. Twenty seven subjects participated in the study and images of their right eye were continuously recorded during the tests. Levels of somnolence, reaction times (RTs), and percentages of lapses were computed for each minute of test. Results show that the values of these three parameters increase significantly with sleep deprivation. We determined the best threshold on our scale of somnolence to predict lapses, and we also shown that correlations exist with some of the ocular parameters. Our somnolence quantification system has thus significant potential to predict performance decrements of subjects accomplishing a task.

Processing of binary fringe patterns obtained by phase-shifting time-averaged shearography on vibrating objects

Shearography can be used for full-field strain measurements in the field of vibration analysis. It provides the spatial derivative of the optical phase difference of the vibration modes amplitude along the so-called shear direction. The shearographic setup considered here is based on the phase-shifting time-averaged technique. It can easily be applied experimentally, but its drawback is that binary phase patterns are obtained. These phase changes are related to the zeroes of a Bessel function. Retrieving the corresponding displacement maps is not straightforward. Moreover, integration of shearographic results need to be performed, and this step is sensitive to noise in the patterns. In this paper, different processing stages are described, from fringe denoising to integration of the displacement maps. The application on data acquired in industrial environment illustrates the good performances of the proposed method.

Artificial defects in CFRP composite structure for Thermography and Shearography nondestructive inspection

Locating defects in CFRP composite materials is a hot topic in nondestructive inspection (NDI). Beside classical NDI technique, such as ultrasound testing (UT), contactless techniques are actively studied. Generally manufacturers of CFRP structure incorporate artificial defects in the bulk, with different extents and depths, in order to study the performance of a specific NDI technique to detect the defect. One of the most common defects in CFRP is delamination between two layers. This is simulated by inserting teflon sheets which, like air, acts as ultrasound blocker in UT. When such reference part is used to assess NDI performance of thermography or shearography, we only observe respectively the thermal or mechanical response of teflon with respect to external loading used with these techniques. In this work, we assess other possibilities for artificial defects in CFRP matrix. For that a CFRP structure was developed and which incorporates teflon, flat-bottom holes and delamination obtained by the pull-out method. We experimentally studied the signals and we discuss the difference between the various artificial defects methods.