Measuring across modalities: Protophones as acoustic attention-getters in infant object communication

Widely regarded as precursors of speech, protophones show a complexity already at an early developmental stage by being voluntarily controlled, functionally flexible and having phonological characteristics of speech. However, in terms of function, they are considered as not having immediate situation-specific functions, in contrast to speech. This study investigates the topic of protophone function further by examining infants' protophone production during visual, tactile and auditory object communication. In the current study, we examined protophone activity in 47 infants (4-18 months old) during social interactions with their caregivers. The infants were recorded in their home environment, in a rural area in Zambia. Results indicated that the infants produced significantly more protophones when using visual rather than either tactile or auditory (sounds that objects/movements make) object signals. Caregivers also responded more when protophones accompanied visual signals than when they accompanied tactile and/or auditory signals. However, in the absence of protophones, there were no differences in caregiver behaviour/responses. Overall, the present work reveals that vocal precursors to speech may serve as attention-getters within social interactions. This lends further support to infants' early capacity to regulate multimodality in communication and their ability to use protophones with immediate situation-specific functions, further painting a picture of complexity embedded already at an early developmental stage within the linguistic communication system.