To provide a theoretical account of the categorical perception data, Liberman and colleagues worked out the motor theory of speech perception, where "the complicated articulatory encoding was assumed to be decoded in the perception of speech by the same processes that are involved in production" (this is referred to as analysis-by-synthesis). For instance, the English consonant may vary in its acoustic details across different phonetic contexts (see above), yet all 's as perceived by a listener fall within one category (voiced alveolar plosive) and that is because "linguistic representations are abstract, canonical, phonetic segments or the gestures that underlie these segments". When describing units of perception, Liberman later abandoned articulatory movements and proceeded to the neural commands to the articulators and even later to intended articulatory gestures, thus "the neural representation of the utterance that determines the speaker's production is the distal object the listener perceives". The theory is closely related to the modularity hypothesis, which proposes the existence of a special-purpose module, which is supposed to be innate and probably human-specific.