When 1-year-old babies in an experiment were placed on an ambiguous visual cliff and saw an expression of fear on their mothers' faces, what portion of them crossed the cliff?

The answer is: None of them

For most children, we develop a functional ability to distinguish facial expression by the age of 6 or older. there are only 1 facial expression that recognized by 1-year old infants (happy and angry), while the other complex expressions would look generally the same for them.