A partial index of discussion notes is in http://www.cs.bham.ac.uk/research/projects/cogaff/misc/AREADME.html
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: 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
You should find a familiar announcement in the box.
Please examine it carefully, to make sure you see just a familiar sentence. If you see
something wrong, and you are with somebody who sees nothing wrong, please do not say what
you see. Just let the other person or persons continue with the experiment, without your
After looking at the sentence in the box, please close the image because the rest of the
experiment depends on your not having it in sight.
After looking at it, please come back here.
All of this is a development of some of the ideas first presented in my 1978 book
The Computer Revolution in Philosophy: Philosophy Science and Models of Mind
especially the points about the system and the environment containing each other, in
chapter 6 and the ideas about relationships between consciousness and control
architecture in chapter 10.
"Blind Man Sees With Subconscious Eye" by Joe Palca
NPR, December 23, 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
Installed: 19 Oct 2009
Last updated: 8 Dec 2009; 19 Jan 2010; 17 Jul 2011; 5 Mar 2013; 13 Mar 2013; 2 Apr 2014
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School of Computer Science
The University of Birmingham