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.

question - in 1827, john walker, a druggist in a small english town, tipped a splint with sulphur, chlorate of potash, and sulphid of antimony, and rubbed it on sandpaper, and it burst into flame. the druggist had discovered the first friction-chemical match, the kind we use to-day. it is called friction-chemical because it is made by mixing certain chemicals together and rubbing them. although walker's match did not require the bottle of acid, nevertheless it was not a good one. it could be lighted only by hard rubbing, and it sputtered and threw fire in all directions. in a few years, however, phosphorus was substituted on the tip for antimony, and the change worked wonders. the match could now be lighted with very little rubbing, and it was no longer necessary to have sandpaper upon which to rub it. it would ignite when rubbed on any dry surface, and there was no longer any sputtering. this was the phosphorus match, the match with which we are so familiar. according the paragraph what was the benefit of the new phosphorus match? it burst into flame when rubbed on sandpaper. it was made by mixing chemicals. it could be ignited on any dry surface. it threw fire in all directions.

answer - matches required natural chemicals