I remember reading at some point in the literature that humans are unable to avoid distraction from a certain primary task if this task isn't using up close to all available 'resources' - basically meaning that everytime the human brain has cognitive resources left, they'll be allocated to one thing or another.
Is that right? If not, at what point is my understanding wrong? Can you give a relevant reference concerning this question?
Edit: I'm referring to distraction in the context of traffic from the perspective of the individual driver.
Hancock, P. A., Mouloua, M., & Senders, J. W. (2009). On the philosophical foundations of the distracted driver and driving distraction.