Why the “Transmission Gap” in Attachment Research: Differential Susceptibility to Rearing Influence?*

A major challenge to students of attachment theory is what van IJzendoorn (1995) has referred to as the “transmission gap”—the gap between what can and cannot be explained about the determinants of attachment security in infancy. Theory suggests that the most important determinants of attachment security should be the sensitivity with which mother cares for the child, yet the predictive power of measured sensitivity appears to be modest (de Wolfe and van IJzendoorn 1997), even though experimental research clearly demonstrates that sensitivity causally contributes to the development of attachment security (van den Boom 1994, van IJzendoorn et al. 1995). Relatedly, while mothers' own state of mind with respect to attachment, as measured by the adult attachment interview, has proven to be rather strong (van IJzendoorn 1995), the presumed mediating mechanism—namely, maternal sensitivity—has not. So again we are confronted with the reality that our power to predict attachment security via maternal sensitivity is nowhere near what we would expect on the basis of theory. Why is that?

Three possible—and nonmutually exclusive—explanations to this conundrum are considered in this chapter. First I will consider what might be labeled “the measurement gap,” that is, that limitations of measurement may result in underestimates of the effects of sensitivity on attachment security. Next I will consider the possibility that insufficient attention has been paid by students of attachment theory to what might be regarded, from the mother's perspective, as “time on task,” and from the infants as the sheer