I found an interesting study out of the University of Rochester that suggests infants like things that are neither too novel or too complicated, the "Goldilocks Effect."
For years, researchers have explored what types of events most effectively capture babies’ attention. In some situations, infants reliably prefer familiar items, such as a favorite toy; in others, they favor novel objects.
The new study resolves such seeming contradictions. Instead of novelty or familiarity per se, the research shows that babies seek out situations with just the right amount of surprise or complexity.
Read the full article, "Babies zero in on ‘just right’ to learn" and/or the original research study, "The Goldilocks Effect: Human Infants Allocate Attention to Visual Sequences That Are Neither Too Simple Nor Too Complex."