ACHI 2015 : The Eighth International Conference on Advances in Computer-Human Interactions Copyright (c) IARIA, 2015. ISBN: 978-1-61208-382-7 224 Two Dimensional Shapes for Emotional Interfaces: Assessing the Influence of Angles, Curvature, Symmetry and Movement Daniel Pacheco Laboratory of Synthetic Perceptive, Emotive and Cognitive Systems. (SPECS) Universitat Pompeu Fabra. Roc Boronat, 138. 08018 Barcelona, Spain. Email: dapachec@gmail.com Sylvain Le Groux Department of Psychology Stanford University 450 Serra Mall Stanford, CA 94305 Paul F.M.J. Verschure Laboratory of Synthetic Perceptive, Emotive and Cognitive Systems. (SPECS) Universitat Pompeu Fabra. Institució Catalana de Recerca i Estudis Avançats (ICREA) Barcelona, Spain Abstract—Recent investigations aiming to identify which are the most influential parameters of graphical representations on human emotion have presented mixed results. In this study, we manipulated four emotionally relevant geometric and kinematic characteristics of non symbolic bidimensional shapes and anima- tions, and evaluated their specific influence in the affective state of human observers. The controlled modification of basic geometric and cinematic features of such shapes (i.e., angles, curvature, symmetry and motion) led to the generation of a variety of forms and animations that elicited significantly different self-reported affective states in the axes of valence and arousal. Curved shapes evoked more positive and less arousing emotional states than edgy shapes, while figures translating slowly were perceived as less arousing and more positive than those translating fast. In addition, we found significant interactions between angles and curvature factors both in the valence and the arousal scales. Our results constitute a direct proof of the efficacy of abstract, non-symbolic shapes and animations to evoke emotion in a parameterized way, and can be generalized for the development of real-time, emotionally aware user interfaces. Keywords–Affective Computing; Emotional interfaces; Graphi- cal User Interfaces; Emotional Design; Expressive Interfaces. I. I NTRODUCTION In the recent years, several efforts have been made in the field of Human Computer Interaction (HCI) to design and implement computer systems that can recognize and express emotion. A number of models have been developed to interpret physiological measurements [1], or behavioural records of body and facial expression in real time [2], and today, reliable ways of monitoring users emotions are being incorporated in commercial systems, such as Microsoft Kinect. On the other hand, models for the expression of emotion — which are usually based on psychological research — have been shown to coherently convey emotion to humans by manipulating human- like or anthropomorphic emotional stimuli. Specifically in the field of Computer Graphics, models for the synthetic expres- sion of emotion using Computer Generated Imagery (CGI) have traditionally involved the use of so called avatars, i.e., virtual characters that simulate human facial expression [3][4], or body movement [5][6], to express a particular emotion explicitly (for a review see [7]). However, it is well known that humans not only respond to human-like or symbolic emotional stimuli. In the literature on music and emotion, for instance, it has been shown that musical parameters such as tempo, pitch or tonality may profoundly affect a person’s affective state [8][9][10]. Since most of the interactive systems with which we interact today present bidimensional user interfaces that are non-symbolic / non-anthropomorphic, it is relevant to identify what are the most important graphical parameters of emotion in simple forms and animations that can be used to generate such interfaces. Furthermore, the advent of new communication technologies allows today for the real time generation of highly parameterized CGI which offers great possibilities for the design and implementation of emotionally aware user interfaces. How can we identify the geometrical and cinematic properties of 2D shapes and animations that have more impact on emotion, and make use of this knowledge in the design of affective HCI systems? Based on literature presented in Section II, we defined an experimental setup to investigate this question by assessing the influence of four specific graphical parameters of shapes and animations on emotion: angles, curvature, symmetry and speed of movement (Section III). Our results show that it is pos- sible to experimentally induce emotional states in controlled environments by parametrically tampering these geometric and kinematic characteristics. The specific impact of each one of them is discussed in Section IV. In Section V, we present our conclusions and future work. II. SHAPE, MOVEMENT AND EMOTION A. Shape The relationship between non symbolic graphic features and emotion has been studied from different perspectives. One approach mostly adopted in the Image Retrieval field has been to study global image features and assess their effectiveness in conveying specific emotions. Several parameters of color (i.e., hue, brightness or saturation [11]), and textures (i.e., coarseness, contrast and directionality [12]), have been shown to influence the affective states of human observers. Similar parameters have been identified in saliency-based visual mod- els (i.e., colour, intensity, orientation and symmetry [13][14]) which can predict human fixations, although, to our knowl- edge, the relationship between saliency and emotion models has not been studied.