X-Message-Number: 14278
From: Brent Thomas <>
Subject: interesting current tests of conciousness
Date: Wed, 9 Aug 2000 14:52:29 -0400 

something to follow up on the conciousness and identity discussions
nothing earthshattering but its interesting to see some actual experiements
that define some of the 
mechanical behavior involved.

from http://www.newscientist.com/news/news.jsp?id=ns225131
From New Scientist magazine, 12 August 2000.

                               CANADIAN researchers have witnessed the
emergence of a conscious
                               thought. Using imaging scanners to measure
brain activity, they recorded the
                               moment when volunteers became conscious of
images appearing in front of
                               them--and found that it all depends on how
many neurons are firing in the

                               Ravi Menon and his colleagues at the
University of Western Ontario showed
                               people patterns of black and white stripes.
While keeping the width of the
                               stripes the same, they increased the contrast
slightly with each image they
                               showed. The volunteers were asked to press a
button as soon as they could
                               see a pattern appearing. 

                               At first, the observers spotted no pattern at
all. But when the contrast reached
                               about 2 per cent they started pressing the
button to show that they could see
                               the stripes. The researchers imaged the
brains of the volunteers continuously
                               during the experiment, using a non-invasive
method of brain imaging called
                               fMRI. This visualises the amount of oxygen in
the blood, a measure which
                               correlates with neural activity. There was an
increase in brain activity in the
                               primary visual cortex of all the volunteers,
corresponding to each button press,
                               and the signal got stronger as the pattern
became easier to see. "The neurons
                               fire more as the contrast increases," says

                               But the researchers could spot the signals
even before the volunteers started
                               pressing the button. "They first pushed the
button at 2 per cent. But we saw a
                               detectable response at 1 per cent," says
Menon. He argues that the difference
                               between an unconscious response to the
stripes and a conscious one is all
                               down to the level of brain activity. "You
need a certain number of neurons to
                               fire to cross the threshold into
consciousness," he says. 

                               Cognitive neuroscientist David Perrett of the
University of St Andrews agrees.
                               "Considering the number of neurons firing is
the only way to think about
                               consciousness," he says. "Consciousness is
brain activity." But psychologist
                               Max Velmans of Goldsmiths College in London
says that is just part of the
                               story. He argues that other elements, such as
which neurons are firing and at
                               what frequency, influence consciousness. "If
you go to the cinema," he says,
                               "all of your visual neurons are firing. Then
you feel something crawling up
                               your leg. The signals from your leg in terms
of energy are far less than the
                               flooding of your visual system from the film.
But it is more important to attend
                               to your leg." 

                               Neuroscientist Susan Greenfield from the
University of Oxford says the work
                               supports her idea that consciousness is like
a "dimmer switch" that can be
                               turned on gradually. "I am delighted that
they are looking at something
                               quantitative, so that we can look at degrees
of consciousness," she says. 

Brent Thomas
Optio Software

407-774-7800 (phone)
407-774-7801 (fax)

Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=14278