A researcher most likely study an infant's ability to categorize by ______.

A) looking at brain imaging to see if there was a shift when an infant was shown something in a different category
B) seeing if an infant looks longer at a picture of something in a different category from what he or she has been shown
C) observing if an infant reaches for objects that are in a different category from what he or she has in front of him or her
D) studying which objects an infant puts into his or her mouth as the objects are presented to him or her

The most common method of testing infants' ability to categorize is by using the habituation paradigm, in which an infant is repeatedly shown stimuli from one category until they habituate to it, and then shown a new stimulus from a different category. If the infant looks longer at the new stimulus, it is interpreted as evidence that they have recognized the difference between the two categories. This method has been used extensively in developmental research and has been shown to be a reliable measure of categorization ability in infants. Therefore, the best choice is B.