Seeing the Disappearance of Unseen Objects
 
 
Stephen Mitroff1 and Brian Scholl2
 
1Center for Cognitive Neuroscience, Duke University
2Department of Psychology, Yale University
 
 
Full Citation
Mitroff, S. R. & Scholl, B. J. (2005). Forming and updating object representations without awareness: Evidence from motion-induced blindness. Vision Research, 45(8), 691-697.
Introduction
Because of the massive amount of incoming visual information at any moment, we cannot be consciously aware of everything simultaneously. As a result, our perception of the world is a complex give-and-take between physical reality and the inferences made by our brains. This creates room for error, and past research has demonstrated that we can sometimes fail to become consciously aware of salient objects right in front of us. This page contains new demonstrations which illustrate the opposite error: we can become momentarily consciously aware of objects which no longer physically exist. In particular, the disappearance of an unseen object can cause the object to blink back into conscious awareness for a moment -- a seemingly paradoxical phenomenon wherein you can see the disappearance of something you can't see.
 
2 Kinds of Demonstrations
If you are using a Macintosh computer, you can experience the phenomenon most easily and robustly by downloading a demo application.  
 
Otherwise, you can get a small taste of the effect by viewing the online QuickTime demonstrations in your web-browser.
 
Downloadable Macintosh Application
This application is custom software written with help from the VisionShell graphics libraries.
If you have any questions, please contact Steve Mitroff.

Note
To use this application, you must be using a Macintosh computer running OS 9 either natively, or via 'Classic' emulation from OS X.


Instructions for Using Application
1. Download and read these instructions carefully.
2. Download the application by clicking here.
3. Decompress the application archive with a tool such as Stuffit Expander.
4. Double-click the resulting application (which will be called "Disappearance Application").
5. Follow the instructions to experience the effects!
 
Quicktime Demonstrations
The following quicktime movies should be viewable on any computer platform and can give you a taste of the effect. (To download a free Quicktime player, go here.) These movies may be a bit large and choppy, and the spatiotemporal parameters may be slightly different than those used in the experiments, but they should be sufficient to illustrate the basic effects.

Important Notes
It is critical that these Quicktime movies be set to 'loop' infinitely for the effects to work, and it is critical that the resulting motion be reasonably smooth. As such, we recommend that you download the movies via the links below, and then play them on your local hard-drive. (Watching them from within your web-browser may often result in choppy non-looping movies.) If the motion is not smooth, try increasing the memory allocation of your movie-player.

Please read the instructions below before viewing the movies.



Download Movie #1 (Motion-Induced Blindness; 2.6 MB)

Download Movie #2 (Disappearing Disc; 4.4 MB)

Download Movie #3 (Rotating Line; 4.4 MB)


Instructions for Movie #1 (MIB)
This first movie is a basic demonstration of the motion-induced blindness (MIB) phenomenon. (See our paper for discussion and citations.) Your task is to fixate the central white circles and attend to the yellow disc. Throughout the demonstration, you should try to keep your eyes as still as possible, fixated on the white circles: if you move your eyes, the effect will not work. While you are fixating, you should start to experience MIB: the yellow disc will begin to fluctuate in and out of awareness. In reality, it is never leaving the screen. Practice with this demonstration for a minute until you can reliably get MIB episodes to last for around 2 seconds. (It may help to shut shades and turn off lights.)

Instructions for Movie #2 (The Disappearing Disc)
In this movie you will try to see the disappearance of something you can't see. In our study, we asked the following question: What happens if, during MIB, we physically remove the yellow disc from the screen. Since you can't see it anyway, during MIB, this is essentially a change from nothing to ... nothing. Nevertheless, most observers are able to see the disappearance. The tricky part of demonstrating this in a movie is that the phenomenon is really interactive: in our Macintosh demonstration application, for example, the disc disappears while you are holding down a key to indicate that you are experiencing MIB. In an attempt to re-create the demonstration in a non-interactive format, this movie simply makes the yellow disc disappear repeatedly at a regular interval, for about 1.5 seconds at a time. You should try to experience MIB for as long as possible, so that one of the regular physical disappearances occurs when the yellow disc is already invisible. Wait for this to happen, and note what you see... At the moment of the physical disappearance, most observers will momentarily perceive the disc reappear for just a very brief moment as either a dark-blue flash (the 'after-image') or as the yellow disc itself (the 'actual-image'). Try it several times! It helps to attend carefully to the location of the disc (while keeping your eyes still, fixated on the white circle), even when you can't see it during MIB.

Instructions for Movie #3 (The Rotating Line)
Try to experience the effect in movie #2 several times before moving on to movie #3. Note that the percept triggered by the physical disappearance of the disc in movie #2 happens without the physical presence of the disc on the screen -- since the signal that triggers the percept is just the instantaneous physical disappearance itself! Instead, this percept must be generated from some internal visual representation. Now consider: when was this representation stored? Because the yellow disc never changed in movie #2, its representation (that reappears as the flash, coinciding with the physical disappearance) could have been stored during the last moment of conscious experience, just before it disappeared due to MIB. Alternatively, this representation may reflect the state of the object during MIB, even when you can't see it, just prior to the physical disappearance. We distinguished between these two alternatives by changing the object during MIB. In this movie, the yellow stimulus is a vertical line which rotates before it disappears. If the entire rotation occurs during MIB, what will you see when it disappears? Again, you should try to experience MIB for as long as possible, and wait for an instance when the last thing you see before MIB sets in is the vertical yellow line. Then try to maintain MIB until the physical disappearance, and note what you see: a sudden brief flash of the rotated version -- indicating that visual processing of unseen objects continues during MIB, and that this information can later reenter awareness.