School of Computer Science THE UNIVERSITY OF BIRMINGHAM CogX project

Aaron Sloman

This file is available as

A partial index of discussion notes is in


This is a demonstration that you may see something and be totally unaware that you have
seen it, simply because you have not processed the information in the right way. Later,
even when the original object is out of sight, you can sometimes discover (even with
your eyes closed) what you previously saw, because you still have the information
readily available. The qualia were constructed and made available, but not attended to.

However the demonstration will not work for everyone: some people realise immediately
what they have seen, and not everyone who fails to see it responds to the prompts when
the original presentation is out of sight.

I have been using variants of this experiment in talks on vision for different sorts of
audience since the mid 1980s. It usually works on a subset of the audience, e.g. between
about 30% and 70% -- though I have not kept detailed records.

Alternative: view the demo on Youtube
There are two versions of the presentation: one uses this web site with a lot of textual
material explaining what to do, but having to read the text may interfere with some of the

So I have created a video version which can be viewed here:
I would suggest trying that before looking at the non-video version presented below. But
if you are unable to view a Youtube video you may find the version below of interest.

How it works

There is an extended discussion of the issues in See also

Added 13 Mar 2013: Thanks
I am grateful for comments received from Gillian Barker, Andrew Brook, and Ned Block,
after I announced the availability of this demo in a philosophy list in March 2013.

Installed: 19 Oct 2009
Last updated: 8 Dec 2009; 19 Jan 2010; 17 Jul 2011; 5 Mar 2013; 13 Mar 2013; 2 Apr 2014

Creative Commons License

This work, and everything else on my website, is licensed under a Creative Commons Attribution 3.0 License.
If you use or comment on my ideas please include a URL if possible, so that readers can
see the original (or the latest version thereof).
Everything I write is subject to revision as I learn -- so it is usually better to save
links than copies -- which are likely to be out of date.
This web page depends on two others that it links to, and an online image displayed in one of them.

Maintained by Aaron Sloman
School of Computer Science
The University of Birmingham