The Need for Attention to See Change

Posted By :
Comments : 0

The Need for Attention to See Change

What’s the Difference between Looking and Seeing?

A large fraction of traffic accidents are of the type “driver looked but failed to see”. Here, drivers collide with pedestrians in plain view, with cars directly in front of them (the classic “rear-ender”), and even run into trains. (That’s right — run into trains, not the other way around.) In such cases, information from the world is entering the driver’s eyes. But at some point along the way this information is lost, causing the driver to lose connection with reality. They are looking but they are not seeing.

What’s going on? Our findings indicate that the critical factor is attention: To see an object change, it is necessary to attend to it.

To show this, we developed a flicker paradigm in which an original and a modified image continually alternate, one after the other, with a brief blank field between the two (see Figure 1 below). The onset of each blank field swamps the local motion signals caused by a change, short-circuiting the automatic system that normally draws attention to its location. Without automatic control, attention is controlled entirely by slower, higher-level mechanisms which search the scene, object by object, until attention lands upon the object that is changing. The change blindness induced under these conditions is a form of invisibility: it can become very difficult to see a change that is obvious once attended.

To see this effect for yourself, try out the following:


Figure 1. General design of the flicker paradigm. The change in the image (here, the movement of the background wall) is difficult to notice under these conditions — observers will often look at but not see the changing object. This difficulty can remain even after observing the images for several seconds, showing that a detailed representation of the scene is not being stored in memory. However, once attention has “latched onto” the appropriate object, the change is easy to see.

Change Blindness and My Security

Surveillance can be a powerful tool in reducing risk and crime. It can act as a deterrent, and capture footage for law enforcement investigations after an incident has occurred. While operating, a surveillance camera will capture every second 24/7/365. The camera will see all events in real time, but your human monitoring them will not. Studies on change blindness found that after 20 minutes of watching a monitor, a human will miss 80% of all activity on the screen. This is a daunting figure for security and risk managers. But there is a solution.


To counter the human program of change blindness, software developers have created analytics that detect defined events and alert the human monitor in real time. The example below is of a train station with passengers moving about and a train in the station. The anlytics detected a person crossing the tracks,triggering a red alert box to draw the attention of human monitor.



  1. Rensink RA (2002). Change Detection. Annual Review of Psychology,53:245-277. (pdf file)
  2. Rensink RA (2000a). The Dynamic Representation of Scenes. Visual Cognition,7:17-42. (pdf file)
  3. Rensink RA (2000b). Visual Search for Change: A Probe into the Nature of Attentional Processing. Visual Cognition,7:345-376. (pdf file)
  4. Rensink RA (2000c). Seeing, Sensing, and Scrutinizing. Vision Research,40: 1469-1487. (pdf file)
  5. Rensink RA, O’Regan JK, and Clark JJ (2000). On the Failure to Detect Changes in Scenes Across Brief Interruptions. Visual Cognition,7:127-145. (pdf file)
  6. Rensink RA, O’Regan JK, and Clark JJ (1997). To See or Not to See: The Need for Attention to Perceive Changes in Scenes. Psychological Science,8:368-373.

And if you liked this…
check out the Change Detection Database.

Source Author:  Ronald Rensink

Leave a Reply


captcha *