Hyams e Wexler (1993)
Hyams, N. e K. Wexler (1993) “The Grammatical Basis of Null Subjects in Child Language”. Linguistic Inquiry, 24.

Hyams e Wexler (1993); Lillo-Martin (1994) e Rizzi (2000)
- Hyams, N. e K. Wexler (1993) “The Grammatical Basis of Null Subjects in Child Language”. Linguistic Inquiry, 24.
- Lillo-Martin, D. (1994) “Setting the Null Argument Parameters: Evidence from American Sign Language and Other Languages”. In B. Lust, M. Suqer, e G. Hermon (eds.) Syntactic Theory and First Language Acquisition: Cross Linguistic Perspectives, Volume 2: Anaphora. Hillsdale, NJ: Lawrence Erlbaum Associates: 301-318.
- Rizzi, L. (2000) “Remarks on early null subjects”. In M. A. Friedemann e L. Rizzi (eds.) The acquisition of syntax. Harlow, England: Longman: 269-292.