Debriefing
There were two different trial types in this experiment. In one set of trials, you were shown a picture, followed by a blank screen, followed by the picture with a slight change, followed by the blank screen again, followed by the original picture. This was repeated until you saw the change and responded. This is referred to as the ‘blank screen’ condition. On other trials, no blank screen was presented in between presentations of the two different pictures. Most participants show change blindness, or difficulty detecting the difference between the two pictures, in the ‘blank screen’ condition but not in the ‘no blank screen’ condition. Response times in the ‘blank screen condition’ can reach 5 seconds, and even 30 seconds is not unusual at all. In the ‘no blank screen’ condition, however, participants detect the difference much more quickly. Cognitive psychologists theorize that, for a change to be detected, the first picture must be held in working memory and compared to the second picture. When there is a blank screen interval, the first picture is ‘erased’ from working memory and cannot be compared to the second picture. A blank screen is not the only stimulus that can produce change blindness. A 1999 study by O’Regan, Rensink, and Clark found that simply splashing high contrast shapes on the screen as the picture was being changed (but not obscuring the area where the change took place) was sufficient enough to produce change blindness. Presumably the splashes interfere with the working memory representation of the picture enough to prevent comparison to the image that is subsequently presented.