How does modality affect our ability to create a new communication system? This paper describes two experiments that address this question, and extend prior related findings by drawing from a significantly more extensive list of concepts (over 1000) than has been used previously. In Experiment 1, participants communicated concepts to a partner using either gestures or non-linguistic vocalizations (sounds that are not words). Experiment 1 confirmed that participants who gesture 1) produce more strongly ‘motivated’ signs that physically resemble the concepts they represent (i.e., are iconic), 2) are better able to correctly guess the meaning of a partner’s signs, and 3) show stronger alignment on a shared inventory of signs. Experiment 2 addressed a limitation of Experiment 1 (concurrent feedback only in the gesture condition). In Experiment 2 concurrent feedback was eliminated from the gesture and vocal conditions. Gesture again outperformed vocalization on communication effectiveness and sign alignment.