Morelli, G. A., Rogoff, B., Oppenheim, D. & Goldsmith, D.  (1992).  Cultural variation in infants' sleeping arrangements:  Questions of independence.  Developmental Psychology, 28(4), 604-613.

In this study, a group of American middle-class mothers and their infants were compared with a group of mothers and infants from a Mayan village in rural Guatemala.  All of the Mayan infants slept with their mothers or other family members for an extended period of time.  None of the American families slept with their infants on a regular basis.  American mothers reported having to stay awake during night feedings, while Mayan mothers did not have to awaken, only turn to make the breast accessible.  While American mothers had elaborate bedtime routines to get the babies ready for bed, the Mayan mothers have no bedtime routines to coax babies to sleep.  The babies simply fell asleep when sleepy, or were nursed to sleep.

The Mayan families were told that American babies and toddlers are put to sleep in a separate room, and they were shocked  and disapproving when they heard this.  Most Mayan families regard cosleeping as the only reasonable way for a baby and parents to sleep.  Their response to the American way of putting children to bed gave the impression that the practice was almost synonymous with child neglect.  The Mayans sleep with their children because of a commitment to a certain kind of relationship with their children, the idea of which is apparently not shared by most Americans.

A Mayan mother was asked about how she teaches her 1 year old that there are some things not to touch.  The mother said that she just tells the baby "Don't touch it, it's no good, it could hurt you," and the baby nods seriously at mother and obeys, and knows not to touch it.  This same kind of statement was common when Mayan mothers were asked this question.

The interviewer told the Mayan mother that American children do not behave this way.  When you tell them not to do something, they become more interested in it.  The Mayan mother attributed her success in teaching her child to the fact that Mayan mothers sleep with their children, and suggested that because American mothers do not, they do not know their children as well.  The Mayan mothers believe that the children understand their mothers more because of the closeness developed through the cosleeping relationship.  They believe that if children do not feel close, it is harder for them to learn and understand the way of the people around them.
 

In my opinion, this Mayan mother was right on!!!  I have never heard a clearer, more insightful description of the benefits of cosleeping.