Structural priming is a tendency to repeat or more easily process a sentence that is similar in structure to a previously presented prime. For example, passive sentences like "the cat was chased by the dog" are less likely to be produced relative to active sentences like "the dog chased the cat". But if one has heard a passive sentence like "a thief was seen by a guard", then the likelihood of producing the passive sentence is increased. Kathryn Bock first characterized this psycholinguistic phenomenon in 1986 and it is referred to by various names such as Syntactic Priming or Syntactic Repetition. Structural priming appears to depend on the abstract syntactic structures and can be isolated from overlap in words or meanings. Unlike semantic priming, it seems to persist over time and processing of other sentences. It occurs in language development and also cross-linguistically.