Speech and gesture, taken together, comprise minimal units of human linguistic cognition. Following Lev Vygotsky in defining a "unit" as the smallest package that retains the quality of being a whole, in this case the whole of a gesture-language unity, McNeill calls the minimal psychological unit a Growth Point because it is meant to be the initial pulse of thinking-for-(and while)-speaking, out of which a dynamic process of organization emerges. The linguistic component of speech categorizes the visual and actional imagery of the gesture; the imagery of the gesture grounds the linguistic categories in a visual spatial frame.
