That said, I do let Chloe fuss a little, make some noise, etc etc, but if she truly cries, I don't leave her there. She needs to learn to trust in me, which is the major task of the entire first year, according to these psychologists.
The sensorimotor stage in a child is from birth to approximately two years. During this stage, a child has relatively little competence in representing the environment using images, language, or symbols. An infant has no awareness of objects or people that are not immediately present at a given moment. Piaget called this a lack of object permanence. Object permanence is the awareness that objects and people continue to exist even if they are out of sight. In infants, when a person hides, the infant has no knowledge that they are just out of sight. According to Piaget, this person or object that has disappeared is gone forever to the infant.
http://mi.essortment.com/jeanpiagettheo_rnrn.htm
In fact, separation anxiety peaks at around this age! Per Dr. Green's website:
They understand about people leaving before they learn about people returning. They can tell from your actions that you are about to leave. Anxiety begins to build even before you leave.
They can’t tell from your actions that you are about to return. They have no idea when – or even if – you will come back. And they miss you intensely. For them, each separation seems endless.
Dropping a screaming child at day care tugs at parents' hearts. Much nighttime screaming is an expression of separation anxiety. Sleep is a scary separation.
(snip)
The first peak of separation anxiety usually takes place in the second half of the first year, and lasts for about 2 to 4 months, though there is great variability in this.
http://www.drgreene.com/21_1183.html
What this says to me is that prior to the development of object permanence, the infant remains with the sense that something is lost but they can't cognitively objectify what it is, and they feel lost. When object permanence begins to develop, they experience the loss, and have no sense of the return, an even scarier time for the infant.
Erikson also referred to infancy as the Oral Sensory Stage (as anyone might who watches a baby put everything in her mouth) where the major emphasis is on the mother's positive and loving care for the child, with a big emphasis on visual contact and touch. If we pass successfully through this period of life, we will learn to trust that life is basically okay and have basic confidence in the future. If we fail to experience trust and are constantly frustrated because our needs are not met, we may end up with a deep-seated feeling of worthlessness and a mistrust of the world in general.
http://www.learningplaceonline.com/stages/organize/Erikson.htm
What this says to me is that my infant needs to successfully pass through this first year learning that I, and the rest of her world, are trustable. She will pass through the object permanence phase, and if I teach her that I will not leave her to cry alone at night, and can be trusted to return, it will be a smoother transition.
Per Maslow's hierarchy of needs:
THE SAFETY NEEDS
If the physiological needs are relatively well gratified, there then emerges a new set of needs, which we may categorize roughly as the safety needs (security; stability; dependency; protection; freedom from fear, from anxiety and chaos; need for structure, order, law, limits; strength in the protector; and so on). All that has been said to the physiological needs is equally true, although in less degree, of these desires. The organism may equally well be wholly dominated by them. They may serve as the almost exclusive organizers of behavior, recruiting all the capacities of the organism in their service, and we may then fairly describe the whole organism as a safety-seeking mechanism. Again we may say of the receptors, the effectors, of the intellect, and of the other capacities that they are primarily safety-seeking tools. Again, as in the hungry man, we find that the dominating goal is a strong determinant not only of his current world outlook and philosophy but also of his philosophy of the future and of values. Practically everything looks less important than safety and protection (even sometimes the physiological needs, which, being satisfied, are now underestimated). A man in this state, if it is extreme enough and chronic enough, may be characterized as living almost for safety alone.
Although in this chapter we are interested primarily in the needs of the adult, we can approach an understanding of his safety needs perhaps more efficiently by observation of infants and children, in whom these needs are much more simple and obvious. One reason for the clearer appearance of the threat or danger reaction in infants is that they do not inhibit this reaction at all, whereas adults in our society have been taught to inhibit it at all costs. Thus even when adults do feel their safety to be threatened, we may not be able to see this on the surface. Infants will react in a total fashion and as if they were endangered, if they are disturbed or dropped suddenly, startled by loud noises, flashing light, or other unusual sensory stimulation, by rough handling, by general loss of support in the mother's arms, or by inadequate support
http://www.xenodochy.org/ex/lists/maslow.html
What this says to me is that my infant, left alone to experience what could be "unusual sensory stimulation", or the loss of support of my arms, she will ultimately turn to the flight or fight stress response. Which involves:
This response to anything which is perceived as a threat, or potential threat begins when certain primitive parts of the brain send a message to the adrenal glands. These begin a process involving a number of hormones including adrenaline, whose purpose is to prepare the body for vigorous emergency action. The main changes that follow are below.Note: This, in an infant who has cried to exhaustion, will also allow for slower gastric emptying, and therefore the decreased hunger drive over a longer period of time - also accounting for how long they might sleep after an episode of CIO.
Non-essential processes are immediately switched off. In particular, if the body is digesting food, that is stopped immediately, and people notice a feeling of churning of 'butterflies' in the stomach, or feeling nauseous or sick. A number of other changes follow, to make the muscles as strong as possible.
The liver releases glucose into the bloodstream. Fats are released into the bloodstream from the fat stores in the body. These are fuel for the muscles, so oxygen is needed to burn them - so the breathing increases, and those under stress may notice feeling breathless.
Having Fuel and oxygen in the bloodstream, the body needs to get it to the muscles as soon as possible - (remember, the body thinks this is a life or death emergency). So to pump the blood quickly, the heart begins beating far faster - and some people notice palpitations. Blood pressure rises, and some people notice feeling hot or cold - even breaking into a sweat, as the body seeks to dissipate the heat that will be generated by the vigorous muscular activity for which the body is preparing.
Becoming ready for instant action, muscle tension increases, and a person may notice shaking, or becoming restless - fidgeting. If the pattern is continued for long enough, chronic headaches or backache may result.
http://www.david.uk-therapist.com/fightflight.html
My conclusion? CIO is not for my family based on the above research, especially not at six months. However, I do agree that simply making noise doesn't necessarily equate crying it out, and that some of the above consitutes extremes and some of the methods discourage reaching those extremes. I continue to assert that I will not allow my daughter to reach the point of crying as part of a "sleep training" process.
Disclaimer: Of course, I wouldn't fault any other parent their choice to let their baby CIO, sometimes a baby's sleep pattern can be detrimental to the functioning of the family, and I would even go so far as to say should be used as a last resort. Thankfully we aren't there.