Bo-NO-bouba-kiki: picture-word mapping but no spontaneous sound symbolic speech-shape mapping in a language trained bonobo

Abstract

Humans share the ability to intuitively map ‘sharp’ or ‘round’ pseudowords, such as ‘bouba’ versus ‘kiki’, to abstract edgy versus round shapes, respectively. This effect, known as sound symbolism, appears early in human development. The phylogenetic origin of this phenomenon, however, is unclear: are humans the only species capable of experiencing correspondences between speech sounds and shapes, or could similar effects be observed in other animals? Thus far, evidence from an implicit matching experiment failed to find evidence of this sound symbolic matching in great apes, suggesting its human uniqueness. However, explicit tests of sound symbolism have never been conducted with nonhuman great apes. In the present study, a language-competent bonobo completed a cross-modal matching-to-sample task in which he was asked to match spoken English words to pictures, as well as ‘sharp’ or ‘round’ pseudowords to shapes. Sound symbolic trials were interspersed among English words. The bonobo matched English words to pictures with high accuracy, but did not show any evidence of spontaneous sound symbolic matching. Our results suggest that speech exposure/comprehension alone cannot explain sound symbolism. This lends plausibility to the hypothesis that biological differences between human and nonhuman primates could account for the putative human specificity of this effect.

Exploring Group Differences in the Crossmodal Correspondences

“…Another challenge concerns the continuing uncertainty over the very existence of various of the different types of cross-modal correspondence that have been proposed (see Spence, 2011;Spence and Sathian, 2020) (Note 14). Potentially relevant here, the latest evidence would appear to support a potential distinction between sound-symbolic cross-modal correspondences and those that are based on more basic perceptual features (e.g., Bottini et al, 2019;Lacey et al, 2016;Margiotoudi et al, 2022; see also Hung et al, 2017).…”

Resolving the bouba-kiki effect enigma by rooting iconic sound symbolism in physical properties of round and spiky objects

“…Last but not least, if the bouba-kiki effect is actually learned from non-speech audiovisual regularities available in the physical environment, it could also be learned by animals. So far, two recent studies on adult apes suggests that they are not sensitive to the classical bouba-kiki effect 45,46 , while other studies with adult chimpanzees suggest that they are sensitive to other audiovisual correspondences 47,48 . Yet, the apparent lack of sensitivity to the boubakiki effect could be due to several reasons.…”

“…In our interpretation of the mechanisms behind the bouba-kiki effect this parameter is crucial as only real 3D objects can produce sounds when hitting or rolling on the ground. Second, the use in these studies of a great number of novel speech items (20 pseudowords) and of human speech stimuli that are infrequent for apes – even though they have been trained to some of them in one of these studies 46 – could have prevented them to spontaneously form an audiovisual association with a corresponding visual shape. Indeed, spontaneous cross-modal matching tasks have been proven to be difficult for apes, see 48 for an overview.…”

Evidence for compositionality in baboons (Papio papio) through the test case of negation

“…www.nature.com/scientificreports/ naturally referential signals have been assumed to play a central role in the acquisition and the emergence of language (e.g., 41,42 ). Yet, while human adults readily understand iconic signals, this capacity is not always observed in children or non-human animals [28][29][30][31][32] . In particular, great apes fail to readily identify the referent of an iconic gesture or acoustic signal 19,30,32 .…”