Intermittent attention is a phenomenon that occurs when we are subjected to visual stimuli in a rapid series. In principle, when two images are presented between which there are a series of distracting stimuli, the same should continue to be identified but… it is not so. The initial images interfere with the recognition of the second image when they are displayed with a time interval of less than 500-600 milliseconds.
The explanations for this phenomenon are very varied, one of these is the one exposed by Sulla and Di Lollo in 2005. They propose the model of temporary loss of control; according to their theory our attention system is perfectly configured to receive the first figure, this configuration is controlled by a central process. When the first image is presented, this central processor is busy in the processing phase, resulting in a temporary loss of attention that prevents the second image from being perceived. However, this theory does not explain another phenomenon that makes intermittent attention doubly curious: The loss of the second stimulus applies to all images except if we are exposed to faces. The first sequence is a classic of intermittent attention: if the second image appears in a flash between 200 and 400 milliseconds after the first, people normally do not notice it but faces are immune to this phenomenon and those faces are more so. that ... express fear! If the second face expresses fear and the first neutrality or cheerfulness, the intermittent attention decreases. Some of the faces used in the experiment were the following:
Alternate with some of these broken faces: 
Sometimes two perfectly normal faces are placed in a sequence of 20 decomposed faces, on other occasions only one was placed. The 23 students who participated in the experiment correctly indicated normal faces and the emotions they expressed. When only one face was shown, there was an 80% correct answer, with no difference in the type of emotion shown but when two faces were shown, the students identified 30% more emotions as annoyance or fear than those faces they displayed. cheerfulness or neutrality. Although the researchers do not explain why this phenomenon, its cause could be hidden in the instinctive mechanisms related to the recognition of situations and emotions related to danger, distress and painful feelings. People may be carrying a special sensor to detect emotions related to fear and pain, as if it were part of an innate survival mechanism. Thus, the Potter, Staub and O'Connor model which is based on the principle of competition between stimuli in the early stages of processing would be validated. In this way, the intermittent attention would cancel the second stimulus as long as it is no longer significant, especially from an emotional point of view. In short, the apparently simple world of human perceptions becomes more complicated each time.
