Dr. John Kennell and Dr. Marshall Klaus had an article in Pediatrics in
Review Vol 19. NO.1, January 1998 that I think is very good.   It is entilted
"Bonding: Recent Observations that Alter Perinatal Care."  On page 9 the
paper discusses research on the use of hard plastic baby carriers as
opposed to soft carriers.  They found that at 13 months of age 83% of
the babies carried in the soft carriers were securely attached compared
to only 39% of the infants that were carried in the firm infant seats.   Dr.
Kennell told me he is working on a research project right now on
attachement and holding infants.  I can't put my hands on his ph no. right
now but you can write to Dr. Kennell :

John H. Kennell, MD
Professor of Pediatrics
Case Western Reserve University
School of Medicine
Behavioral/Developmental Pediatrics
Rainbow Babies & Childrens Hospital
11100 Euclid Avenue
Cleveland, OH 44106

Ann Twiggs, Ohio WIC Breastfeeding Coordinator