Predictability determines whether our attention fades away.

A universal feature of our sensory systems (vision, audition, touch, etc.) is that they adapt, or habituate, to a repeated stimulus - their reporting grows weaker. The common view is that this decrement in response is due largely to automatic processes in sensory neurons. Doing fMRI measurements of cortical responses to photographs of sequentially displayed faces, Summerfield et al. find evidence of a further 'top-down' mechanism for repetition suppression:

By manipulating the likelihood of stimulus repetition, we found that repetition suppression in the human brain was reduced when stimulus repetitions were improbable (and thus, unexpected). Our data suggest that repetition suppression reflects a relative reduction in top-down perceptual 'prediction error' when processing an expected, compared with an unexpected, stimulus.