Subjects learned to map phrase-structure-defined strings onto geometric figure arrays. "String-generation" subjects produced symbol strings corresponding to arrays; "String-interpretation" subjects constructed arrays corresponding to strings. "Mixed" subjects alternated between these tasks.Subjects' knowledge of symbol sequence acceptability was periodically probed.Mixed subjects learned the structure dramatically faster than other subjects.This suggests that natural acquisition of structure underlying symbol-world mapping systems like language depends on learning multi-directional mappings
