The Phi Effect and a Quarrel about Consciousness

In my recent blog post on rereading Thoreau’s Walden I described how “bubbles of light” danced around the pages of my book as I sat reading under a tree, and also how some of these circles of light seemed to jump from one spot to another. The technical name for this visual “jumping” effect is the Phi phenomenon, and it’s an illusion that is crucial to our ability to process “motion pictures.”   As it happens, this effect has also been discussed by two very different thinkers seeking to explore the nature of consciousness: the philosopher Daniel Dennett and the psychologist Merlin Donald.  Donald describes the phenomenon as follows in his excellent book A Mind So Rare: the Evolution of Human Consciousness:

The simplest demonstration of Phi is to alternate two light sources spaced a few feet apart: on-off-on-off., etc.  At a certain speed of alteration the viewer no longer sees two lights turning on and off but instead reports seeing a single light moving back and forth.  The observer’s brain has unconsciously resolved the alternating images into a single moving picture.

So in my case the light passing through the leaves of the tree above me was dispersed onto the page of my book, producing many circles of light, and these circles moved around on the page, or appeared and disappeared, as a result of the breeze fluttering the leaves.  Apparently the “speed of alteration” was at certain times, and in certain spots on my page,  just right for producing the Phi illusion, so that I began to see a single light jumping back and forth.

Now, what does any of this have to do with consciousness?  That question brings us to Daniel Dennett’s brilliant and provocative book Consciousness Explained, which has sometimes been dubbed by his detractors Consciousness Explained Away, because of Dennett’s relentless determination to do away with our “illusions” about consciousness.  For Dennett, the Phi phenomenon is interesting because it is yet another example of the mind tricking itself.  And the big trick he wants us to see through is our belief that “consciousness” is more powerful, and more prevalent, than it really is.  His argument is detailed, complicated, and lengthy, so I can’t do justice to it here, but it has been quite important to my thinking about mind, and about all the ways our behaviors and decisions are influenced by factors and processes that are, in fact, inaccessible to conscious awareness.  But in A Mind So Rare, Donald takes up a serious quarrel with Dennett, whom he labels both a Minimalist and a Hardliner because of his habit of “downgrading consciousness to the status of epiphenomenon.” In Donald’s view, the Hardliners substitute for consciousness “a computational netherworld deep under the surface of the mind, [so that] old-fashioned consciousness simply slips away from our grasp, fading into the mist.”  I may not have made it entirely clear yet how exactly Dennett and Donald get from the Phi phenomenon to an argument about consciousness, but the debate involves the question of how much importance we should give to illusions like the Phi effect when we try to evaluate our capacity for conscious awareness.  Since I don’t want this to get too long, I think I’ll go a little deeper into this question in another post. For now, I’ll just say that things get especially interesting when you consider the phenomenon of Color Phi, which you can experience here.



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