Though seemingly a good candidate for a universal output-oriented constraint, the OCP does not occur as a constraint in the production grammar. Instead, it handles, in interaction with the No-Crossing Constraint, the correspondence between acoustic cues and perceptual feature values in the perception grammar. Because faithfulness constraints use the perception grammar to evaluate the similarity between the perceptual specification and the perceptual output in the production grammar, the OCP does influence the evaluation of candidates in the production grammar. As a result, adjacent identical elements are avoided because they constitute Parse violations. Dissimilation at a distance, by contrast, is due to a constraint against the repetition of articulatory gestures.