5.5. Inattentional Blindness

Neisser (1979) also investigated the question of selective attention by superimposing two semi-transparent video clips and asking viewers to attend to just one series of actions.  Viewers often were unaware of what went on in the other clearly visible video. Twenty years later, Simons and Chabris (1999) explored and expanded these findings using similar techniques, and triggered a flood of new work in an area referred to as inattentional blindness. Perhaps their most famous study involved participants watching a video like the one below, where they were asked to count the number of passes one of the teams was making. In the middle of the video, a person in a gorilla suit walks across the screen, but nearly 50% of the people missed seeing the gorilla.

Watch this video on the Monkey Business Illusion to learn more about inattentional blindness!

A similar attentional phenomenon is change blindness. Change blindness is when something changes in the environment (or a picture) and you fail to notice. Like inattentional blindness, change blindness is also very common. It explains why we often fail to notice when someone we see every day gets new glasses or a haircut, or shaves off their facial hair. Psychology experiments often investigate change blindness by alternating two slightly different pictures within a video and measuring how quickly participants spot the difference. Can you see the differences between the two pictures in Figure 5.6 – look at the end of this chapter (above the References) to find the answer. Even when there is a large difference between two pictures, about 40% of people fail to find the difference. Simons and Levin (1988) showed that change blindness affects a similar number of people in real world settings. Fifty percent of participants failed to notice that the person to whom they were giving directions changed to a different person! It sounds like a magic trick but check out the Door Study video to see how the researchers managed to make the switch without people noticing.