First, I believe CIO should be done with a specific purpose in mind, i.e. helping a child learn how to fall asleep on his/her own. Keeping this purpose in mind, the parent would then pay attention to the child, taking into consideration sleepy cues, how long the child has been awake, if the child has been fed, etc., and then soothing the child and putting the child to sleep (rather than just putting the child to sleep when the parent feels like it). Then, if the child is put down and begins to cry, the parent does not go to the child to comfort. It does not mean that the parent doesn't listen to the cries or somehow observe the child. The child is left to soothe himself to sleep or after a predetermined time set by the parent, is soothed by the parent. There are different types of CIO...Ferber suggests going in at intervals, Weissbluth suggests not going in at night, but going in after an hour at naptime...or at intervals (he basically suggests Cry, Some Cry, No Cry...whatever works for the parent); Babywise suggests going in after 20-25 minutes. Basically, CIO is supposed to be done to help a child learn to sleep on his/her own and go back to sleep should they wake up in the middle of the night and do not need a feeding. It should be done, however, with responsible parenting.
Re: Define CIO