How can I check for retransmits on my ap?

I am trying to determine if playing with the fragmention settings at my ap will yield better through put. This post is more of a learning post and no real issue exists.

Is there a column I can turn on when watching the wireless interface that would give me stats on retransmits?

If I find there are retransmits I might look into fragmentation adjustment. ( I understand it is better to find the source of the interference but for learning purposes…)

Thanks in advance