Saturday, April 14, 2012

Do you have the time? Some surprising facts about how consciousness works

Surprising fact: The neural signals from a drummer's foot take almost of a third of a second longer than do the signals from the hand when they are playing the same beat.



That's not all.  Whenever you stub your toe, there are pain signals that get to the brain almost a third of a second slower than the others, even though they contribute to the very same pain sensation.

How does the brain work this out to end up with one conscious experience of pain, or of a funky drum beat?  Does the brain wait for the last signal to come in before it puts it all together into a feeling?  Or can it revise and resubmit sensory information to the running journal of conscious experience?

An illusion called 'the phi illusion' helps to further illustrate the problem, and how the brain works it out. The result is really quite crazy.

The Phi Illusion

The phi illusion is the reason why we can watch movies and see them as motion rather than as a sequence of still pictures, which is all a movie really is.

For example, here is the first movie ever made: 1st movie ever.  In 1878 Eadweard Muybridge filmed it by lining a stretch of track 12 cameras that went off as a horse ran by.  When we experience the horse's continuous motion means that we are, in a sense, filling in the blanks between pictures.

The illusion is hard to appreciate, because we are so familiar with motion pictures.  But a way to notice the illusion more clearly is to focus on one or two features changing between frames.  Here is an animation of a dot that looks like it's moving back and forth while changing colors, at least for certain settings of the framerate.  But really, it's just two dots, one red and one green, flashing on and off with just the right delay between dots.

When you experience that dot moving back and forth, it seems you must been extrapolationg, somehow, where the dot was between frames of the animation.  And what color it was.  But just what color was it?  And where exactly did you "see" it in between frames?  Are those things somehow registered somewhere in your brain as sensory information?  Or are you just telling yourself a story about what happened and the details are left ambiguous and unexamined by your consciousness?  According to the philosopher and cognitive scientist Daniel Dennett, conscious experience is more like a story you tell yourself about what happened.  There is no "halfway dot" registered anywhere in your visual cortex.



Daniel Dennett has explained this illusion with his "multiple drafts" model of consciousness.  This theory says that we are always making up narratives of "what's going on".  There are usually more than one versions of the story floating around, and its never too late to revise...your consciousness experience is what emerges from an evolutionary-like battle between ideas of what happened.  In the phi illusion, stories that involve motion get selected for so that they end up in the later "drafts" of the story.

The dot appears to move back and forth because when it goes from say, being a red dot on the left to being a red dot on the right, because once that red dot appears we revise the story to include motion, and a color change.

So when a drummer plays a funky beat, he does not have to wait for all the neurons to reach his brain to from his foot as it hits the kick drum before he truly experiences the beat.  And the beat is not experienced as "smeared out" in time, either.  This is despite the fact that multiple kinds of neural signals contribute to the same sensation, some that arrive up to a third of a second later.  Once those straggling neurons deliver their message, the drummer's conscious experience of "the beat" is revised accordingly.


You may have experienced for yourself how the experience of the past can be "retrospectively presented" to the present version of consciousness, say, when you suddenly notice a church bell has been ringing and you are still able to count the chimes, even though you didn't notice it when it started ringing.  You just submitted a new draft that includes revised information about the past.  The versions of your story of consciousness that did not contain bells ringing got beat out by versions that included bells ringing, even though the battle took some time.

Okay, that's all I have time to write.  Or at least that's what I'm telling myself.



Here are some more links for the phi illusion, and related illusions:

1 comment:

David Haas said...

Hi,
I have a quick question about your blog, do you think you could email me?
David