Operationalizing intentionality in primate communication: Social and ecological considerations
An intentional transfer of information is central to human communication. When comparing nonhuman primate communication systems to language, a critical challenge is to determine whether a signaller intends for the recipient to derive a particular meaning from the message contained in the signal. As it is not possible to directly observe psychological states in any species, comparative researchers have inferred intentionality via behavioural markers derived from studies on pre-linguistic human children. Recent efforts to increase consistency between nonhuman primate communication studies undervalue the effect of possible sources of bias: some behavioural markers are not generalizable across certain signal types (gestures, vocalizations, and facial expressions), contexts, settings and species. Despite laudable attempts to operationalise first-order intentionality across signal types, a true “multimodal” approach requires integration across their sensory components (visual-silent; contact; audible), as a signal from a certain type can comprise more than one sensory component. Here we discuss how the study of intentional communication in non-linguistic systems is hampered by issues of reliability, validity, consistency, and generalizability. We then highlight future research avenues that may help to understand the use of goal-oriented communication by opting, whenever possible, for reliable, valid, and consistent behavioural markers, but taking into account sampling biases and integrating detailed observations of intra-specific communicative interactions.