Proceedings of the 2 nd International Conference on Timbre (Timbre 2020), 3-4 September 2020, Thessaloniki (online), Greece Timbre and Visual Forms: a crossmodal study relating acoustic features and the Bouba- Kiki Effect Ivan Eiji Simurra 1,2† , Patrícia Vanzella 2 and João Ricardo Sato 2 1 Music Department, Federal University of Acre, Rio Branco, Acre, Brazil 2 Center of Mathematics, Computing and Cognition, Federal University of ABC, São Bernardo, São Paulo, Brazil † Corresponding author: ieysimurra@gmail.com Introduction Music has a multidimensional nature with a myriad of features set over time that vary in a multitude of acoustic profiles. It has been shown, for instance, that music listening may be a multimodal experience where musical sounds can evoke abstract visual forms. Particularly, we are interested in a well-described effect known as the Bouba-Kiki effect (Köhler, 1929). This phenomenon relates to a non-arbitrary tendency to associate abstract words whose utterance demand rounding sounds (as in Bouba) with rounded shapes, while sharp words (as in Kiki) are usually associated with angular shapes. The studies based on the bouba- kik effect provide the first vital clues to understand the origins of proto-language, as it suggests that there may be natural restrictions on the way sounds are mapped on objects. Previous research suggests that this cross-modal phenomenon may also be found between musical timbre and shapes (Adeli et al, 2014). The authors studied the cross-modal correspondences between musical timbre and visual forms. Basically, using visual stimuli based on the literature about the Bouba-Kiki effect, each sound stimulus with timbre variation was related with some peculiarities of shapes, that is, rounded or angular. For the music orchestration and timbre studies, contemporary music, particularly from the Second Half of the 20 th Century and the 21 st Century music compositions, have made extensive use of technical procedures to draw attention to novel sound characterization features, such as texture and the presence of noisy sounds as relevant sound events. Such prospect is delved in the context of non-standard instrumental techniques concurrent to the usage of alternative musical orchestration settings. The present study focuses on the cross-modal correspondences between the acoustic correlates of contemporary orchestral music and the visual forms from the Bouba- Kiki Effect. We carried out an online experiment to collect ratings from subjects listening to contemporary music excerpts. Then, we cluster the classification to summarise results and then we analyze them by the acoustic features from auditory stimuli. Method The sound stimuli database was designed to address contemporary music techniques and practices aimed at the creation of new sounds and textures in orchestral writing (Griffths, 1978). A total of eleven sound stimuli were selected each with a duration of 5.0 second. Audio mixings were created using Audacity and the instrumental audio samples used to generate the orchestral sound textures belong to three sound databases (Ballet et al, 1999). The audio fragments were chosen from excerpts of chamber music and orchestral works by composers such as Ravel, Debussy, Stravinsky, Messiaen, Schoenberg, Ligeti, Grisey, Scelsi, Lachenmann, Xenakis and Sciarrino. Accordingly, such compositions and instrumental techniques may be explored to create unexpected sound effect modifying the global timbre perception. For the visual shapes we selected forms with different structures between rounded and jagged features. For that, we settled our assortment based on the study performed by Nielsen and Rendall (2011). On the first step of the experiment, we gathered data from an online survey in order to select the most appropriate visual shapes by listening each of the auditory stimulus. Fifty-one volunteers (30 women, age average = 34.79, sd ± 9.80) rated each auditory stimulus with one of the ten abstract shapes alternatives. To avoid fatigue effects and