According to Michael Tomasello, one of two abilities essential to the uniquely human ability to acquire language. While the pattern-finding ability allows pre-linguistic infants to begin to identify one linguistic unit from another, the use of these units requires intention-reading skills, which transform linguistic stimuli from statistical patterns of sound into fully fledged linguistic symbols. In other words, this stage involves 'connecting' the meaning to the form, which gives rise to the form-meaning pairing that make up our knowledge of language. Only then can these linguistic sounds be used for communication. This process takes place when, at around a year old, infants begin to understand that the people around them are 'intentional agents': their actions are deliberate and the actions and states of others can be influenced. The emergence of this understanding allows infants to 'read' the intentions of others. The human intention reading ability, as it manifests itself in first language acquisition, consists of three specific but interrelated phenomena: joint attention frames, the understanding of communicative intentions and role reversal imitation.