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Change Blindness

introduction and background
online examples
software(purpose, applet, software)
selected publications

Background and Examples

What are we really aware of when we look out into our world? The phenomenon of "change blindness," when large changes in scenes go unnoticed, is causing many scientists to reevaluate their understanding of the visual process. To understand this phenomenon, one must experience it to believe it. Try some online examples to experience the phenomenon for yourself.

If you haven't experienced this before, it may be quite suprising. After all, most people believe strongly that they would notice such changes if in similar situations. Leven et al. demonstrate these same misconceptions are an experimental setting and explore some of the reasons why such overestimations may occur (2000).

How much of what we percieve do we actually process, and finally, bring to conscious awareness? A number of studies on change blindness have posited the idea that instead of storing complete knowledge about the world in our memory, we use the world itself as an "external" memory source. Only specific attention on a part of the visual space allows that area to be represented in memory (O'Regan 2001). Others argue that memory provides a more detailed description of the environment than the attention theory allows (Hollingworth et al. 2001).

Regardless, much has be learned from studies of the change blindness phenomenon, and there is still vast amounts to be discovered (for reviews: Simons and Rensink 2005, Thompson and Pessoa 2000, O'Regan and Noe 2001).

Online Examples

Kevin O'Regan Centre Universitaire de Boulogne. Subtle changes over time in pictures.
Daniel Simons University of Illinois. Changes in real life situations, motion-pictures, and gradual changes.
Ronald Rensink University of British Columbia. Classic flicker examples.

Purpose of Our Software

Gaze Tracker
The program we have designed here allows simple experiments on eye movements during a classic change blindness task. When a person views their world, the place where their eyes focus is the only area that is sharply defined visually - the rest is blurry and provides less specific visual information. To simulate an eye tracker (a device which records the trajectories of gaze and, therefore, which parts of the image a subject is focusing on), we allow the user to see only a small circle of sharp image at a time. To change focus in the picture, the user must drag the mouse, which moves the focus circle, to another section of the picture. In this way, areas of focus can be recorded, as well as time spent in an area. When the user finds the part of the picture that is changing, they can click on it, which stops the flickering and allows one to save the foveation image.

Questions to Ask
Questions that could be asked with this software could be, "Do subjects look at more salient objects more often?", "What is the average percentage of the picture that is scanned before a subject finds the change?," "Can a change not be detected yet focused on?" etc.

Both the Java applet version and the downloadable software contain two sets of the same pictures. One set of pictures is blurred, and the other is dimmed. Questions that could arise from the comparison of these two conditions could be, "Does object recognition help change detection?", "Is there a difference in patterns of gaze between the two conditions?" etc.

Java Applet

Applet. link to both dim and blurred examples. (Does not work with Safari)

How to use the applet..
Choose an image. (You may want hide the explorer toolbars on your browser to ensure that the full picture is shown on the screen.) When the applet loads, move the magic window around until you can find the area that is different between the two pictures. Click once you've found it. You'll then see an image that shows where you've been, with dark areas indicating places you never looked, and clearer areas corresponding to areas you visited more often. Once you've found the change and clicked, you can copy the image that shows where you've been.

How to save an image from the applet..
pc: copy the image to the clipboard using "alt" and "print screen" together. Then open a new microsoft word document and paste in the image.
mac: hold down the "shift", the "ctrl", the "command" (which looks like an apple key) and then press the 4 key. The cursor will turn into a crosshairs and you can click and hold on the upper-left portion of your picture, and drag the rectangle down to the bottom-right corner. When you release the mouse button the image will be on the clipboard and you can paste it into a word document.
Note: This may not work under Safari on the mac unless java is upgraded to version 1.4.2.


Change Blindness Application(7.6 MB) Contains images as well as application. After downloading, right-click on the link and then save it to your desktop. Find the file and then right-click on it to unzip it. Then find the .zip file and uncompress it by clicking on it. Finally, find the ChangeBlindness.jar file and double-click on it to run the program.

Introductory Movie(10.4 MB) Best way to quickly learn how to use the application.

Selected Publications on Change Blindness:

  1. Change blindness: Past, present, and future. Simons, D.J., and Rensink, R.A. (2005a). Trends in Cognitive Sciences, 9: 16-20. (pdf)
    Provides an up-to-date overview of the study of change blindness. Good place to start to find other articles of particular interest. Critiques suggested implications of change blindness research and posits questions for future directions in the area of study.
  2. Blindness to scene changes caused by "mudsplashes". O'Regan, J.K., Rensink, R.A., Clark, R.A. & J.J. (1999). Nature, 398, 34. (pdf)
    Short article describing 'mudsplashes' technique in causing change blindness phenomenon, and discusses implications for the nature of mental representations and attention.
  3. Neural correlates of change detection and change blindness. Beck, D. M., Rees, G., Frith, C. D. & Lavie, N. (2001). Nature Neuroscience, 4, 645-650. (pdf)
    Study using fMRI to show neurological differences in change detection versus change blindness. Beginning attempts to discover the neural correlates to awareness of change.
  4. Beyond the grand illusion: what change blindness really teaches us about vision. Noe, A., Thompson, E., Pessoa, L. (2000). Visual Cognition, 7, 93-106. (pdf)
    Qualifies more extreme assumptions on the implications of change blindness for lack of mental representations of the visual environment.
  5. expanded version of talk given by J.K.O'Regan & A. Noë at ASSC 4, Brussels, June 29-July 2, 2000, and by J.K. O'Regan at Bressanone, Jan 21-26, 2001. (pdf)
    Long but incredibly fascinating look at the philosophical implications of change blindness on our conscious experience of perceptions.
  6. Change blindness blindness: The metacognitive error of overestimating change-detection ability. Levin, D.T., Momen, N., Drivdahl, S.B., & Simons, D.J. (2000). Visual Cognition, 7, 397-412. (pdf)
    Explores the issue of why people are so suprised when experiencing the change blindness phenomenon, and why they are overconfident of their ability on such a task.
  7. Scene context and change blindness: Memory mediates change detection. Hollingworth, A., Williams, C. C., & Henderson, J. M. (2001). Psychonomic Bulletin & Review, 8, 761-768. (pdf)
    Refutes the theory that change can only be detected when subject's attention is focused on area of change.