Since the 1995 release of  "Meaningful differences in the everyday experience of young American children" by Betty Hart and Todd Risley (Brookes Publishing, Baltimore, MD), much has been published in support of (and more recently challenging) the premise of the Word Gap deficit. A summary of Hart and Risley's findings can be found here.

Students in Doug Medin's Learning Sciences 451 - Diversity in Learning Sciences (Fall, 2014) took on the Word Gap and other issues. Resulting papers are below.

Saiyed, G. & Smirnov, N. (2015) OpEd: Does '30-Million Word Gap' Have Gap in Authenticity? The Youth Project.

Image is Everything

Further reading:

Quenqua, D. (2014). Quality of Words, Not Quantity, Is Crucial to Language Skills, Study Finds. The New York Times, Oct 16, 2014.