What you see and hear depends on what you focus on. It is also called selective listening. There was an experiment where the subjects were asked to count the number of passes in a basketball game. The control group were asked to just watched the game. A person is a gorilla suit ran out in the middle of the court. Many of the people in the group that was busy counting did not see the gorilla person. Whereas the control group had no problem noticing the gorilla.
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