Change Blindness
We experience the world as a continuous experience, but the human visual system actually takes snapshots of the world every 40 milliseconds or so. Our brain then pieces these snapshots together so that it feels like a fluid experience even though it is not.
The Flicker Paradigm
Each time the visual system gets a new snapshot of the world, it masks the previous snapshot. This will be demonstrated in this lab activity using the flicker paradigm. In ten experimental trials, you will be presented with a flickering picture where you will try to identify what is changing. As soon as you detect what is changing, you will press the spacebar. After you complete all trials, your response times to identify what is changing in the scene will be shown.
Manipulations That Induce Change Blindness
There are two types of trials in this lab activity. In the first type, the “blank screen condition,” a picture is shown followed by a blank screen, followed by a slightly changed picture, followed by the blank screen again, followed by the original picture. In the second type, the “no blank screen condition,” no blank screen is presented in between the presentations of the two slightly different pictures. Change blindness is the difficulty detecting the difference between two pictures. Most people show change blindness in the “blank screen” condition but not in the “no blank screen” condition. This is clear from inspection of response times that in the “blank screen condition” can reach up to 5 seconds or sometimes as long as 30 seconds. But in the “no blank screen” condition, response times indicate much quicker detection.
Change Blindness and Working Memory
Why is it so much more difficult to detect change in the “no blank screen” condition? It is thought 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 between the two pictures, the first picture is erased from working memory and therefore is not available to be compared to the second picture. Researchers have also discovered that in addition to a blank screen to induce change blindness, flashing high-contrast shapes on the screen as the picture is being changed can also cause change blindness even when the shapes are presented in an area far from the changed region (O’Regan, Rensink, and Clark).
Everyday Relevance and Applications
There are a number of practical implications from what you learned in this activity. The inability to detect a change can easily result in a car accident. It is no wonder that many states have instituted no texting while driving laws since even very short glimpses away from the road can interfere with detecting change and result in change blindness. The design of dashboard warning signals especially in aircraft benefits tremendously from cognitive studies, which show the importance of not having other unrelated things changing around a warning display at the same time since they can interfere with working memory and cause change blindness.