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Tuesday, July 1, 2014

Infant Eye Contact and Visual Development-- How They're Related

Of all the posts I’ve posted on this site over the years, the one that gets read over and over again is about eye contact between infants and caregivers ( People seem to be looking for information on this subject because they’ve read that there is an “epidemic” of autism, that autism can be detected through certain “red flags” like the absence of eye contact, and because they quite reasonably believe that early detection allows early intervention and early intervention supports typical development. In fact, there is actually no epidemic, but statistics about autism have been inflated by changing the criteria for diagnosis; whether “red flags” are diagnostic of autism depends on the baby’s age, because younger children typically show some behaviors that are also found in older autistic children; and whether early intervention is effective for autism is still open to question.

Still, worrying is a feature of the natural history of parenthood, and we’re all likely to worry about whatever problem we see or hear most about. Seventy years ago, parents worried about polio, and before that, about tuberculosis. When autism is understood and cured one day, there will be different worries!

I don’t propose to be able to make people stop worrying about autism. However, I think it’s possible that if some aspects of development were better understood, there might be less concern about eye contact with very young babies. I have been thinking about this because I’ve had several similar comments recently on the post linked above. These were queries from mothers who were concerned that their babies seemed to look at people across the room from them, to make eye contact and smile and generally be sociable, but not to do this in response to someone who was holding them. It seemed all too easy to interpret the behavior as not “liking” or “being attached to” the holding person, and by extension to say that there was something wrong with social relationships, and therefore there might be autism developing.

Neither I nor anyone else can guarantee that a certain baby will NOT later be diagnosed as autistic, on the basis of that baby’s behavior at a few months of age. However, I think that if we look at some details about development, we’ll see that there are reasons why a baby might look at and be interested in a more distant person and not a nearer one. (Warning: This is complicated, and you might not want to plough through the whole thing--  but it’s one of those things where you either have the details, or you have only a vague and useless statement.)

The important issue here is about how vision changes with development. If a baby is going to make eye contact or smile in response to someone else’s smile, he or she has to be able to see the eyes or the smile, and this ability develops gradually during infancy. (It does not become really adult-like until about age 6 years.) All babies, autistic or typically developing, go through these changes in vision, which are more complex than you might think.

A lot of parents today know that newborns have very little clear vision other than at a fixed focal distance of about 8-12 inches from the eye. Where most people get confused, though, is in thinking that at a distance of 8-12 inches a young baby can see the same image an adult would see. This is not correct. A newborn sees in daylight the same amount of detail an adult would see in moonlight. In addition, babies have poor acuity (the ability to see small details). At age one month, the acuity is about 20/250, meaning that the baby can see at 20 feet away the same size details that an adult with good vision can see at 250 feet. At age 3 months, acuity is still no better than 20/150. And, keep in mind that a baby cannot do any of the things adults can do to improve their view of an object--  they can’t get closer, turn on a brighter light, or hold the object at a better angle.

But what I’ve just said suggests that young babies ought to be able to see near things better than far things, when they can see them at all. So what explains the queries about babies looking at a distant person and not a near one? Here’s where a couple of complicated things come into the  picture. The first is a matter called a contrast sensitivity function. This basically means that if you make a graph showing how bright a light needs to be in order for a baby to see something, that graph will show that not everything is equally easy to see. In order for babies to be able to see narrow lines, they need the lines to have high contrast--  to be black and white rather than grey and white or pink and powder blue. (Interestingly, one of the people who has done a lot of work about newborns imitating facial expressions, Andrew Meltzoff, had really black eyebrows and a contrasting pale face; I’ve often wondered whether a blond could have had the same success!)  

If the lines are medium-sized, babies can see them even when they are of lower contrast and the light is dimmer. Human eyes seem to be specialized for a certain size of detail and level of contrast; this is true for adults too. But here’s the really counterintuitive piece: when the lines are broad, they are harder to see, and the baby needs more contrast and more illumination to see them. This is exactly the opposite of what we would assume--  we expect big things to be easy to see, small things to be harder, but it’s not so. How does this apply to babies looking at faces? Well, when a face is farther away, its image on the eye is smaller, making it more like the easy-to-see  medium “stripes”. When it’s close, its image is larger, making it more like the hard-to-see broad stripes. This means that the baby needs brighter light to see that a face is a face, but if we are bending over the baby, chances are that our faces are in shadow.

[I know this seems like a strange phenomenon, but I should point out that it occurs at the other end of life too. Elderly people lose sensitivity to broad stripes. When we get right in their faces, they may not be able to recognize us, or even to be sure that what they see is a face. Backing off a bit may enable them to see who is there.]

There’s more to be discussed here, if anyone is still with me. How about the baby’s ability to recognize a shape? This too changes in the first months. Newborns tend to move their eyes to look at the edges of any shape, including a face. After about 6 weeks they still do this, but at the same time will spend some time looking at details within the outline. (And guess what, this is about the time that many babies begin to smile back at a smiling face occasionally.) Details about the eyes are often very attention-getting for young babies--  they are shiny, they move, and there is often high contrast between the iris and the “white” and between eyelashes and pale skin or between dark skin and the “white”. (Does this mean young mothers should be encouraged to wear a lot of eye make-up? It couldn’t hurt, certainly!)

One more thing to consider here: part of a baby’s vision depends on the ability to use the eyes together, and to move them so they are looking at the same object at the same time. This ability, convergence, is much more important for near objects than for distant objects. (You can show this to yourself by looking at a near object and then covering first one eye and then the other. You’ll see that you actually have different “pictures” of the object seen by each eye, with extra information coming from the differences between the pictures. Try it again with a distant object--  the two eyes get pretty much the same picture.) Convergence on a near object is quite inconsistent until the baby is about 2 months old, and still takes a lot of time until about 3 months. This means that an adult can quickly look from a near to a far object or vice-versa, but a young baby cannot. When convergence is good, babies can use a lot of information from it to help figure out how far away something is and therefore what it might be. Is it something that is actually an interesting human being, or is it a doll or a picture? What’s obvious to adults may be a puzzle to a young baby.

I hope this shows the parallels in development of visual ability and in expression of interest in other people. When a baby does not make eye contact, the reason may well be that his or her visual development is not sufficient to identify a face under certain conditions of light or distance. Let’s not wave any “red flags” until that possibility is ruled out!

N.B. To save space, I have not given sources for this information, but I have them available if anyone wants them.

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