Abstract
Joint attention - parents' and children's coordinated attention to each other and to a third object or event - is believed to play a causal and critical role in early word learning. However, joint attention, as conventionally defined and measured, relies only on overt indicators of attention, is studied predominantly in the visual modality, and varies by culture. Moreover, word learning can occur without joint attention in typical development, in autistic development, and in Williams syndrome, and joint attention can occur without commensurate word learning in Down syndrome. Thus, the assumption that joint attention is a necessary and sufficient precursor to vocabulary learning is not universally supported.