Answer: Inattentional blindness
Explanation: Simply this phenomenon occurs due to the perceptual preoccupation with certain subjects, in this case white shirts, which is why they do not see certain phenomena, although they are within the field of view of the participants. That is why this blindness is also called perceptual blindness. In other words, participants' perceptions were influenced by being told to focus only on white shirts, and their perception was somehow "directed". Because of this, half of the participants did not see man wearing the black gorilla costume, if he was in some white costume, the participants would probably have seen him.
Head of state or chief of state...i think :)
