Stereopsis typically does not appear until approximately ___________ months after birth.

• A. 2 months
• B. 3 months
• C. 4 months
• D. 6 months

Answer: (B)

Stereopsis depends on proper eye alignment (fusion) and the brain’s ability to compare the two slightly different images from each eye. After birth, these systems mature gradually, and behaviorally measurable depth perception starts to appear around a few months of age. Approximately three months is the typical onset window, when infants begin to show depth discrimination in tasks that rely on binocular disparity. Earlier than this, around two months, the binocular system isn’t consistently capable of producing true stereopsis, while by four to six months it becomes more robust. So, three months best matches the common developmental timing for the appearance of stereopsis.