Bodily constraints contributing to multimodal referentiality in humans: The contribution of a de-pigmented sclera to proto-declaratives

•Eye-gaze significantly contributes to multimodal referentiality in cooperative tasks.•Disrupting it decreases performance of tasks that require coordination of attention.•A de-pigmented sclera might have been a prerequisite in establishing common ground.•Multimodal referentiality underlied vocal intentional communication in our ancestors.

We present the results of an empirical study that measured the contribution of a conspicuous eye-gaze (as a function of scleral de-pigmentation) of humans in conveying multimodal referentiality by combining visual and auditory cues in a naturalistic setting. We made participants interact in a cooperative task in which they had to convey referential meaning about co-presential entities. In one of the conditions, participants had no access to their interactants' eye-gaze. We interpret the results as supporting the idea that our eye morphology contributes to instantiating multimodal referentiality in cooperative tasks in peripersonal space.