What concept is illustrated by the following study? Participants were instructed to focus on either white or black objects, disregarding the other color. When a red X moved across the screen, about one third of the subjects did not notice it.

   Inattentional blindness

Explanation:  This kind of blindness does not occur due to some defect in the organic sense, so everything is okay with the eyes, it is blindness that arises as a psychological effect. For this reason, this blindness is also known as perceptual blindness because it arises as the result of the perception of one who observes, therefore, attention is directed to another object, in this case black and white. Therefore, since all the attention are directed at the observation of another black white and objects, when something that is not initially indicated to be observed appears, like red X, it escapes attention, that is, the observer is inattentionally "blind" to that unexpected object. This is, therefore, a rejection of something that is unexpected, though completely visible, because the task given has drawn all our attention to other objects or the other side.

the answer is d.index