Emotion Detection and Recognition based on Brain and Peripheral Physiological Signals

Emotions affect and determine social relationships and interactions, memory and creativity, and influence the mechanisms of rational thinking and decision making. The influence of emotion on decision making has gained attention in computer science. By detecting and recognizing emotions in an automatic way, machines endeavor to ease interaction between users and multimedia content. Automatic emotion detection and recognition can be carried out through analysis of users' various behavioural, and physiological signals such as electroencephalogram (EEG), electrocardiogram (ECG), electrodermal activity (EDA), and respiration, among others. These modalities have been extensively studied individually. However, since different individuals may experience the same emotion but express it differently, the various modalities are considered complementary, and fusion of various physiological and behavioural responses is expected to improve the quality of emotion recognition systems. Nevertheless, although representative features and their multimodal integration have been studied in affective computing research for various applications, patterns that arise from the dynamic interrelation among various modalities during emotional processes have received less attention. By summarizing each physiological signal only in a number of features, one may lose information present in the underlying dynamical co-evolution of various physiological signals. Considering all these issues, this thesis aims at detecting and recognizing emotion through brain and peripheral signals, targeting three complementary topics that have not been thoroughly explored. The first one includes emotion assessment from music video clips, the second one emotion assessment from odors, and the third one Quality of Experience (QoE) assessment from two-dimensional (2D) and three-dimensional (3D) video contents, using in all cases brain and peripheral physiological signals. Regarding emotion assessment from music video clips, subject-dependent and subject-independent analyses are carried out in this thesis, and the results reveal that although there are differentiations among the subjects' brain activation patterns, there are still common patterns across them. Moreover, the dynamical co-evolution between EEG and EDA is explored during emotional processes, and the results reveal that the coupling between EDA and EEG of the temporal lobe increases when strong emotions occur with respect to neutral ones. Finally, possible clustering patterns across subject-categories are investigated, and the results reveal that there are common characteristics across subject-categories related to their emotions. Regarding emotion assessment from odors, since the primary response to odors is related to pleasantness perception, which has not yet been thoroughly investigated, this thesis explores the way perceived odor pleasantness influences brain and periphery. In particular, two independent classifiers are trained and tested, one using EEG and the other using ECG features. The results reveal that it is possible to assess odor pleasantness perception from EEG and less accurately from ECG features, in a subject-independent framework. Also, decision fusion of the EEG and ECG classifiers is shown to discriminate odor pleasantness perception. Moreover, in order to explore the dynamical co-evolution between brain and peripheral signals, the coupling between heart rate and EEG is investigated. The results reveal that there is a significant increase in the coupling between ECG and temporal lobe EEG, when pleasant or unpleasant odors are experienced with respect to neutral ones. Enhanced QoE from multimedia contents targets to increase users' sensation of reality, in order to induce stronger emotions and render the user more involved in the experience. In this thesis, QoE is investigated in terms of four aspects, namely perceived depth, perceived overall quality, content preference, and sensation of reality. In particular, it is revealed that it is possible to recognize perceived depth, content preference, and sensation of reality from EEG signals, but not from the peripheral ones. Also, fusion between peripheral and EEG features is found to improve the performance in some cases. Finally, the left frontal cortex seems to be activated when sensation of reality is high, indicating that high sensation of reality is related to approach-related emotional processes. Although the three topics are independently explored in this thesis, their potential integration would endeavor to create immersive multimedia systems, which could adapt their properties according to users' emotions, and enhance, thus, user-experience.

Social Network Analysis for Automatic Role Recognition

Sarah Favre

The computing community has shown a significant interest for the analysis of social interactions in the last decade. Different aspects of social interactions have been studied such as dominance, emotions, conflicts, etc. However, the recognition of roles has been neglected whereas these are a key aspect of social interactions. In fact, sociologists have shown not only that people play roles each time they interact, but also that roles shape behavior and expectations of interacting participants. The aim of this thesis is to fill this gap by investigating the problem of automatic role recognition in a wide range of interaction settings, including production environments, e.g. news and talk-shows, and spontaneous exchanges, e.g. meetings. The proposed role recognition approach includes two main steps. The first step aims at representing the individuals involved in an interaction with feature vectors accounting for their relationships with others. This step includes three main stages, namely segmentation of audio into turns (i.e. time intervals during which only one person talks), conversion of the sequence of turns into a social network, and use of the social network as a tool to extract features for each person. The second step uses machine learning methods to map the feature vectors into roles. The experiments have been carried out over roughly 90 hours of material. This is not only one of the largest databases ever used in literature on role recognition, but also the only one, to the best of our knowledge, including different interaction settings. In the experiments, the accuracy of the percentage of data correctly labeled in terms of roles is roughly 80% in production environments and 70% in spontaneous exchanges (lexical features have been added in the latter case). The importance of roles has been assessed in an application scenario as well. In particular, the thesis shows that roles help to segment talk-shows into stories, i.e. time intervals during which a single topic is discussed, with satisfactory performance. The main contributions of this thesis are as follows: To the best of our knowledge, this is the first work where social network analysis is applied to automatic analysis of conversation recordings. This thesis provides the first quantitative measure of how much roles constrain conversations, and a large corpus of recordings annotated in terms of roles. The results of this work have been published in one journal paper, and in five conference articles.

EPFL2011

Brain-Computer Interface in Multimedia Systems

Ashkan Yazdani

A brain-computer interface (BCI) is a system that allows a user to communicate with the environment only through cerebral activity, without using muscular output channels. To establish a direct link between the brain and a computer, the electroencephalogram (EEG) signal of a user is measured and then analyzed with the help of signal processing and machine learning algorithms. Once a certain mental activity has been detected by the computer, a response can be displayed on a screen or a command can be sent to a peripheral device, for example a wheelchair or a television. The main application area for BCI is assistive technology for handicapped people. For example, one can imagine artificial limbs controlled by a BCI, a BCI-based spelling device, or an environment control system based on a BCI. Nevertheless, during the last years it has been convincingly shown that communication via a BCI is feasible for able-bodied as well as handicapped users and several new applications such as entertainment and gaming, and neuro-feedback have been proposed for BCI systems. This thesis describes the author’s contributions to the research on brain computer interface systems, focusing on exploring and studying new applications of BCIs especially in multimedia communication domain. After providing a general overview of the EEG signal processing techniques and current BCI systems, three topics of interest have been identified. These topics include BCI for salient image retrieval and image triage, BCI for affect recognition during multimedia consumption, and BCI for studying the EEG correlates of pleasant and unpleasant odors. In the first topic, we present a BCI system, capable of identifying interesting images in an image database. Using this system, images of a database are presented to several users at a fast rate, and the information on whether a given image is salient, is implicitly extracted by means of processing the EEG signals, acquired when users are watching the image sequence. Furthermore, in order to investigate the impact of expertise on a BCI-based salient image retrieval system, the changes in the EEG signals of expert and novice users (with respect to image content) are studied. We show that it is possible to define experimental protocol and judiciously apply signal processing tools such that a practical BCI system can be set up for detection of interest in users during the watching of image sequences. Furthermore, we show that a relatively high retrieval accuracy can be obtained for most of the users of this system. The second presented topic deals with an affective BCI system, which recognizes the emotional states of users While they watch different music video clips. More precisely, the users are asked to watch several emotive music video clips, while their EEG and other peripheral physiological signals are acquired. Signal processing and machine learning algorithms are then developed to infer the emotional state of the user, induced while watching the music video clips. We propose the application of this BCI system in implicit emotional annotation of multimedia contents and sketch a iii iv road map towards developing a hybrid BCI system for emotional search and retrieval of multimedia contents. In the last topic, we present the results of our study on exploring the EEG alterations during the perception of pleasant and unpleasant odorant stimuli. We identify the regions of the brain cortex, which contribute to differentiation of pleasant and unpleasant odors and show that a relatively high accuracy for classification of EEG signals during perception of hedonically different odorant stimuli can be achieved. Furthermore, we identify a novel clinical application for the developed system, namely to study the EEG changes in comatose patients during stimulation with hedonically different odors in order to estimate the depth of coma.

EPFL2012

EEG-based Recognition of Covert Attentional Shifts

Catherine Brandner, Ricardo Andres Chavarriaga Lozano

Attentional shifts precede most of the perceptual processes, and therefore their recognition may constitute an interesting process for both the study of human perception as well as the design of EEG-based Brain Computer Interfaces (BCI). Several studies have focused on EEG modulations of spatial attention, pointing out to changes in both Alpha and Gamma bands (Thut et al. 2006 J. Neurosci 26:9494; Tallon-Baudry and Bertrand 1999 T Cogn Sci 3:151; Jensen et al. 2007 TINS 30:317). This work aims at further characterization of EEG correlates of attention shifts to evaluate their potential use in BCI applications. We recorded 32-channel scalp EEG while subjects covertly shift their attention towards one out of several spatial targets. Consistently with previous studies, characterization of the spatio-temporal patterns using time-frequency analysis (Morlet wavelet transformation), shows main modulations in the alpha and gamma frequency bands. Moreover, it is also shown that these modulations are characterized by intermittent episodes of activity (Palix et al. 2006 Perception 25:234). Furthermore, we assess the EEG-based recognition of spatial attention -time and target location of the shift- using a machine learning approach based on the detection of informative, episodic activity. The proposed approach is based on the hypothesis that recognition may be improved by identifying the moments where the underlying neural phenomena is more salient (e. g. the appearance of episodic oscillations related to attentional shifts), and performing the classification based mainly -if not exclusively- on the activity during these periods. Our results show accurate recognition of attentional shifts (>75%) based on the scalp EEG signal. Moreover, the proposed approach allow us to efficiently detect endogenous processes loosely synchronized to external events. These results provides evidence supporting the feasibility of using attentional processes in Brain-Computer Interfaces.

2008