On the Emergence of Compositionality

Compositionality is a hallmark of human language words and morphemes can be factorially combined to produce a seemingly limitless number of viable strings. This contrasts with nonhuman communication systems, which for the most part are holistic encoding a whole message through a single, gestalt form. Why does every human language adopt a compositional strategy? In this paper, we show that compositional language can arise automatically through grounded communication among populations of communicators. The proposed mechanism is the following: if a holistic and a compositional approach are in competition and if both structured (compositional) and atomic meanings need to be communicated, the holistic strategy becomes less successful as it does not recruit already acquired bits of language. We demonstrate the viability of this explanation through computer simulations in which populations of artificial agents perform a communicative task describing scenes that they have observed. Successful language strategies (that is, those yielding successful transmission of information about a scene) are reinforced while unsuccessful ones are demoted. The simulations show that this reinforcement on the basis of communicative success indeed leads to the dominance of compositional language as long as the fraction of unstructured meaning to be communicated is sufficiently high. Moreover, following Elman (1993), we then show that the same effect can be achieved by, instead of manipulating the world (the fraction of unstructured meaning presented to the agents), letting the agents themselves go through developmental stages. These simulations confirm that simple reinforcement mechanisms applied during communicative interactions can account for the emergence of linguistic compositionality.