Editing Origin of language (section)

=== Tool-use associated sound in the evolution of language ===
Proponents of the motor theory of language evolution have primarily focused on the visual domain and communication through observation of movements. The ''Tool-use sound hypothesis'' suggests that the production and perception of sound also contributed substantially, particularly ''incidental sound of locomotion'' (''ISOL'') and ''tool-use sound'' (''TUS'').<ref name="Larsson2015">{{Cite journal |last=Larsson |first=M |year=2015 |title=Tool-use-associated sound in the evolution of language |journal=Animal Cognition |volume=18 |issue=5 |pages=993–1005 |doi=10.1007/s10071-015-0885-x |pmid=26118672 |s2cid=18714154}}</ref> Human bipedalism resulted in rhythmic and more predictable ''ISOL''. That may have stimulated the evolution of musical abilities, auditory working memory, and abilities to produce complex vocalizations, and to mimic natural sounds.<ref>{{Cite journal |last=Larsson |first=M |year=2014 |title=Self-generated sounds of locomotion and ventilation and the evolution of human rhythmic abilities |journal=Animal Cognition |volume=17 |issue=1 |pages=1–14 |doi=10.1007/s10071-013-0678-z |pmc=3889703 |pmid=23990063}}</ref> Since the human brain proficiently extracts information about objects and events from the sounds they produce, ''TUS'', and mimicry of ''TUS'', might have achieved an iconic function. The prevalence of sound symbolism in many extant languages supports this idea. Self-produced ''TUS'' activates multimodal brain processing ([[motor neuron]]s, hearing, [[proprioception]], touch, vision), and ''TUS'' stimulates primate audiovisual mirror neurons, which is likely to stimulate the development of association chains. Tool use and auditory gestures involve motor-processing of the forelimbs, which is associated with the evolution of vertebrate vocal communication. The production, perception, and mimicry of ''TUS'' may have resulted in a limited number of vocalizations or protowords that were associated with tool use.<ref name="Larsson2015" /> A new way to communicate about tools, especially when out of sight, would have had selective advantage. A gradual change in acoustic properties, meaning, or both could have resulted in arbitrariness and an expanded repertoire of words. Humans have been increasingly exposed to ''TUS'' over millions of years, coinciding with the period during which spoken language evolved.