APA (7th ed.) Citation

Gullberg, M., & Indefrey, P. The earliest stages of language learning.

Chicago Style (17th ed.) Citation

Gullberg, Marianne, and Peter Indefrey. The Earliest Stages of Language Learning.

MLA (9th ed.) Citation

Gullberg, Marianne, and Peter Indefrey. The Earliest Stages of Language Learning.

Warning: These citations may not always be 100% accurate.