Search under "speech" in Medline. Speech problems are closely linked to
artificial feeding and the deficits are worse in boys. The pacifier and
"sucking objects" articles I've found certainly confirm that concept. I
don't have a bibliography compiled, but I bet it wouldn't be too hard.

My youngest had severe speech and language delays and required many years of
therapy, DESPITE being breastfed over 4 years. Lack of oxygen at birth is a
huge factor, as is altered oralmotor mechanics caused by artificial teats.
Some children have hearing problems, often related to ear infections, which
may result in delayed speech. My son's receptive language was fine - his
problems were in expressive language and articulation.

IF this guy is blaming breastfeeding for the delay, seek another opinion
PRONTO. He is way off base.

Linda J. Smith, BSE, FACCE, IBCLC
Bright Future Lactation Resource Centre
Dayton, OH USA
http://www.bflrc.com