The importance of parity; its implications for understanding speech perception

Early in his career, Alvin Liberman obtained experimental findings that he describes in his book, Speech: A Special Code, as ‘‘an epiphany.’’ The findings revealed that listeners track speakers’ articulations. From these findings and subsequent others, Liberman developed his motor theory of speech perception. In addition, however, he set out to understand why listeners track articulation. His explanation was that humans evolved a phonetic system jointly responsible for producing coarticulated speech and for recovering intended phonetic segments from coarticulated signals. Underlying the claim that production and perception are linked in this way is the idea of parity. In Liberman’s interpretation, parity is the requirement that, for language to serve as a major component of human communication systems, listeners and talkers must agree on what set of perceivable human actions can count as components of a linguistic message. In addition, and more concretely, in their conversational interactions, listeners a...