Unfourtuantly, this is so well established that it is hard to find research. I did find this paper [1] which looks into how babies acuire word boundries. As you

Unfourtuantly, this is so well established that it is hard to find research. I did find this paper [1] which looks into how babies acuire word boundries. As you identify, there are probably phonetic cues; but not pauses. The best way to see this is to try listening to a language you do not understand, and try to identify word boundries. Indeed, the paper I link argues that some phonetic cue must exist because babies can recognise word boundries. [1] https://www.ncbi.nlm.nih.gov/pubmed/8176060 https://www.ncbi.nlm.nih.gov/pubmed/8176060