Why does this guy act like I'm invisible?

This guy in my lab group at school acts like I'm not there. If someone from my lab group and I are studying a diagram and he wants it, he will ask her if she's done. Not me. If he asks the other two girls in my group a question he will completely leave me out. He is very outgoing and not at all shy so I wouldn't think it was intimidation. I'm just confused...what would be the reason for him to ignore me?
Why does this guy act like I'm invisible?
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