SalNichols…..When we are overloaded the brain cannot do anymore it is overloaded so it starts to filter. One of the first seances it filters is the sense of hearing. It can be seen in the simulator when everything is going to hell and the alarms are not cancelled even though they are blaring away in the background, the other pilot will give you an instruction and you may not even register it. It was taught to me in Human Factors during my ATPLs way back when and also demonstrated in CRM classes. I don't know the reference but Im sure someone here will….I'm not making it up…and I am far from a great pilot.