Aaron Sloman

Originally posted with title "Unconscious seeing".

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 processes.

To avoid that, a video version can be viewed here: http://youtu.be/qKPfy9IufG4
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
  • http://www.cs.bham.ac.uk/research/projects/cogaff/misc/blackmore-zen-consciousness.html
    Some comments on Susan Blackmore's little book "Zen and the Art of Consciousness" (Previously published as "Ten Zen Questions").

  • This is a small part of the Meta-Morphogenesis project

  • Some of the processes of mathematical discovery involve similar mechanisms, since such discoveries often involve noticing an aspect of what you were previously conscious of, but did not notice. Examples, using experiences of triangles can be found in this draft paper: Hidden Depths of Triangle Qualia. Theorems About Triangles, and Implications for Biological Evolution and AI The mechanisms involved seem to be closely related to mechanisms required for perception and use of various kinds of affordances (including types not noticed, or discussed, by James Gibson). There are more mathematical examples in this discussion of "Toddler Theorems"

    For more on the need to generalise Gibson's theory of affordances (and fix broken theories about the functions of vision in animals and future robots) see this presentation: What's vision for and how does it work?

  • This report on a case of blindsight is also relevant
    "Blind Man Sees With Subconscious Eye" by Joe Palca NPR, 23 December, 2008
    Blind Man Unknowingly Navigates Obstacle Course
    Watch A Video Of The Experiment. (Joe Palca, Kathleen Masterson)
    "TN has what is known as blind sight, according to de Gelder. Even though the primary part of his brain that processes visual information is destroyed, he still has more primitive parts of his brain intact, and these are capable of doing some visual processing. After all, one of the most basic functions of the visual system is to help an animal avoid obstacles or predators. TN still has some visual abilities - he's just not aware he has them."

  • For more philosophical and logical fun and challenges see Ron Barnette's web site:
    Zeno's Coffeehouse including an online mind-reader partly related to this site.
    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: 12 Jun 2019;
    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