The mental starburst

Eminent astrophysicist Neil de Grasse Tyson was talking about the unreliability of the human sensory-perceptive system -- how, despite our confidence in what we see and hear, so often it is inaccurate or incomplete -- and said, "You know those trick drawings... optical illusions?  Well, that's not what they should call them.  They should call them 'brain failures.'  Because that's what they are.  A few cleverly drawn lines on a sheet of paper, and your brain can't handle it."

I've been interested in optical illusions -- or brain failures, if you prefer -- for a long time.  I think the feature of this phenomenon that intrigues me the most is the fact that even once you know what's going on, you still can't see it for what it is.  Here's one of the best examples of that I've ever seen:

Japanese artist Kokichi Sugihara created this, and others like it, that defy our expectation of how the world works.  Note that when the whole apparatus is rotated, and you see how it's done, it doesn't help.  You'd think your knowledge that gravity does indeed pull things toward the Earth, plus your knowledge of how exactly your eye was tricked, would be enough for the brain to go, "Oh, okay!  I get it now!  Duh!"

But no.  He rotates the apparatus back to its original configuration, and presto!  Upside-down gravity again.

The reason the topic comes up is because of a paper in the journal Perception this week about a fascinating illusion called the "scintillating starburst."  Here's what it looks like:

What do you see here?  If you're like me (and apparently most people), besides the obvious dark interlocking polygons, you see a pattern of light-colored lines radiating out from the center.

You've undoubtedly already guessed what the problem is; those lines don't exist.  Your brain, in effect, created those lines.  But how?  And why?

The authors write:

[The scintillating starburst illusion is] a unique kind of stimulus that evokes ghostly or ephemeral illusory rays that appear to shimmer or scintillate... We ascertained that the [effect] experienced by observers when viewing this stimulus type is modulated by all stimulus dimensions we suspected to be relevant when piloting the study, namely the number of vertices of the polygons, contrast, the line width of the wreaths, the number of wreaths, and whether the polygons are bisecting or not. The strongest effect was yielded by the number of wreaths, followed by whether the strands are bisecting, stimulus contrast, line width of the braids, and the number of vertices of the polygons, in that order...  [N]o stimulus dimension by itself produces a strong effect, only the optimal confluence of many stimulus parameters does so.  We believe that these results are consistent with probabilistic inference—for instance, the percept of illusory lines from an occluder is more likely if there are more intersection points where the vertices bisect, and if this happens at higher contrast.  This is not implausible, as deciding on a coherent interpretation of ambiguous visual information is a fundamental challenge faced by the visual system.  Of course, probability by itself is not sufficient—the specific stimulus situation matters—for instance, a row of street lights does not evoke the impression of a bright band that connects them.  But in the case of street lights, the bright beacons are broken up by the darkness of the night.  This darkness is unambiguously present.  However, in the case of Starbursts, the bright beacons are separated by background of the same color, yielding the percept of an occluder of that color on top of the stimulus.

What I find puzzling about this explanation is the last bit -- that we don't see a bright band connecting streetlights at night, because there is the unambiguous presence of darkness between the lights -- doesn't really account for seeing bright lines where none exist.  After all, the entire background is the same color; our brains generate an illusion that the vertices of the polygons are connected by radial lines even though the entire area is unambiguously the same shade of gray.

What I'd like to see is how the brain is actually responding -- perhaps fMRIs of people looking at the polygons with no braiding and concentric patterns, then a pattern of actual radial lines, then the illusion itself.  My guess is that the last two would activate the same parts of the brain and the first would not.  It might not explain why it happens, but at least we'd see what module is being tricked.

So here we have once again an example of how our brains, when confronted with quite ordinary stimuli, proceed to make shit up.  

Think about that next time you're tempted to say, "Of course it happened that way.  I saw it with my own eyes."

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One of the most devastating psychological diagnoses is schizophrenia.  United by the common characteristic of "loss of touch with reality," this phrase belies how horrible the various kinds of schizophrenia are, both for the sufferers and their families.  Immersed in a pseudo-reality where the voices, hallucinations, and perceptions created by their minds seem as vivid as the actual reality around them, schizophrenics live in a terrifying world where they literally can't tell their own imaginings from what they're really seeing and hearing.

The origins of schizophrenia are still poorly understood, and largely because of a lack of knowledge of its causes, treatment and prognosis are iffy at best.  But much of what we know about this horrible disorder comes from families where it seems to be common -- where, apparently, there is a genetic predisposition for the psychosis that is schizophrenia's most frightening characteristic.

One of the first studies of this kind was of the Galvin family of Colorado, who had ten children born between 1945 and 1965 of whom six eventually were diagnosed as schizophrenic.  This tragic situation is the subject of the riveting book Hidden Valley Road: Inside the Mind of an American Family, by Robert Kolker.  Kolker looks at the study done by the National Institute of Health of the Galvin family, which provided the first insight into the genetic basis of schizophrenia, but along the way gives us a touching and compassionate view of a family devastated by this mysterious disease.  It's brilliant reading, and leaves you with a greater understanding of the impact of psychiatric illness -- and hope for a future where this diagnosis has better options for treatment.

[Note: if you purchase this book from the image/link below, part of the proceeds goes to support Skeptophilia!]