A recent experiment conducted in Japan suggests that eye contact draws on the same mental resources used for complex tasks, so trying to maintain eye contact can impede your reasoning. In this case, the break in eye contact comes not from emotion, but from the need to preserve cognitive resources. Eye contact can deplete your mental bandwidth.
You'll find me doing this very often. I need all my mental resources for composing responses and maintaining fluency. So many assume 'lying' based on ancient psychology tomes.