COGNITIVE PSYCHOLOGY 19, 498-550 (1987) Structural Packaging in the Input to Language Learning: Contributions of Prosodic and Morphological Marking of Phrases to the Acquisition of Language JAMES L. MORGAN University of Minnesota RICHARD I? MEIER Stanford University AND ELISSA L. NEWPORT University of Illinois The linguistic input to language learning is usually thought to consist of simple strings of words. We argue that input must also include information about how words group into syntactic phrases. Natural languages regularly incorporate cor- related cues to phrase structure, such as prosody, function words, and concord morphology. The claim that such cues are necessary for successful acquisition of syntax was tested in a series of miniature language learning experiments with adult subjects. In each experiment, when input included some cue marking the phrase structure of sentences, subjects were entirely successful in learning syntax; in contrast, when input lacked such a cue (but was otherwise identical), subjects failed to learn significant portions of syntax. Cues to phrase structure appear to facilitate learning by indicating to the learner those domains within which distributional analyses may be most efficiently pursued, thereby reducing the amount and complexity of required input data. More complex target systems place greater premiums on efficient analysis; hence, such cues may be even more crucial for acquisition of natural language syntax. We suggest that the finding that phrase structure cues are a necessary aspect of language input reflects the limited capacities of human language learners; languages may incorporate structural cues in part to circumvent such limitations and ensure successful acquisition. 0 1987 Academic Press, Inc. This research was supported in part by grants to J. Morgan from the University of Min- nesota Graduate School Faculty Research Fund; by NICHD Grant T32-HD07151 to the Center for Research on Learning, Perception and Cognition, University of Minnesota; by NIH Grant NS-16878 to E. Newport and T. Supalla, by NIH Training Grant HD-07205 to the University of Illinois; and by NIMH Grant MH 15157to Stanford University. We thank Data Ginsberg for her diligent work in running the subjects and scoring the data for Experi- ment 3. We also thank Charles Pike for explicating the intricacies of Swahili concord, and Steven Pinker and two anonymous reviewers for their helpful comments. Richard Meier is currently at the University of Texas, Austin. Reprint requests should be sent to James L. Morgan, Institute of Child Development, University of Minnesota, 51 East River Road, Minneapolis, MN 55455. 498 OOlO-0285187 $7.50 Copyright D 1987 by Academic Pre%. Inc. All rights of reproduction in any form rewved.