What is true about the series of visual cliff experiments?
◦ Infants younger than 6 months do not have depth perception.
◦ Three-month-olds showed heart rate acceleration, which means they recognized the depths were different.
◦ Twelve-month-olds crossed or didn't cross the cliff based on their mother's facial expression on the other side.
◦ Three-month-olds' slowed heart rate showed that they understood the different depths and were thus hesitant to cross the visual cliff.