CHESS

There will be two talks, the first one presented by Denis Fantinato, and the second one by Raphaëlle Roy.

Raphaëlle Roy
Title The DynEmo project: Eye-fixation related potentials of emotional facial expressions

Abstract The processing of emotional facial expressions (EFE) elicits specific evoked brain responses that enable us to better understand at what stage the differentiation of the valence and nature of these emotions occurs. Typically, these evoked responses are investigated using the event-related potential technique (ERP). However, in order to assess more subtly the time course of EFE processing, it seems more appropriate to use eye-fixation related potentials (EFRP) thanks to the co-registration of electro-encephalography and oculometry. Moreover, only this technique can allow an investigation of the impact of specific face features, such as the eyes, on the brain responses to EFE. Objective: This study was designed to investigate how the evoked potentials elicited by natural emotional facial expressions are impacted by four emotion conditions (for both ERPs and EFRPs) –happiness, surprise, disgust, neutral- as well as the face region of interest – eyes, nose and mouth – in the case of EFRPs. Methods: Twenty-four participants underwent the experiment. They had a first session during which they passively explored the pictures of natural but standardized EFE of the DynEmo database, and a second one during which they had to label them. Main results: The eyes elicited significantly more fixations but lower amplitudes for all components than the nose, which in turn elicited more fixations and lower components’ amplitude than the mouth. Moreover, the disgust condition elicited more fixations on the nose and less on the eyes than the other emotions, and the happiness and surprise conditions elicited more fixations on the mouth than the other emotions. At the electrophysiological level, the distinction between emotions appeared around 220 ms post-stimulation for the ERPs with significantly different amplitudes for the P2P3 complex and the LPP component, and even earlier for the EFRPs with modulations of the N170 component, mostly at the left frontal electrode sites. The face region was critical as the mouth elicited higher components’ amplitude than the nose, and the nose than the eyes at central and parieto-occipital sites. There was also an interaction between the face region and the emotion, with notably a distinction between surprise and disgust on the mouth for the P2P3 complex.

Denis Fantinato
Title: From Blind Deconvolution to Nonlinear Blind Source Separation in the Context of Statistically Dependent Sources

Abstract: This presentation will discuss about two problems in the signal processing area: that of blind deconvolution and that of nonlinear blind source separation, both considering statistically (temporally) dependent sources.
In the former case, the problem admits solution – based on results obtained in my PhD research – if certain a priori dependence information is at disposal, which is a valid assumption in some applications, like that of channel equalization. This idea will be presented under the light of the matching of multivariate distributions, using the Parzen window method for PDF estimation.
In the second case, for my stage at GIPSA, we focus on a new perspective of the field: the use of the derivatives of the mixtures. Interestingly, a possible approach is to explore the statistical independence among the sources by jointly considering the mixtures and its derivatives – an idea that could be accomplished through the use of multivariate distributions. Some other possibilities of work will be presented for discussion/suggestion.