Let not thy left hand know what thy right hand doeth (oh, fishmongers - you so crazy…)

In my day job, I’m grateful - if a bit confused - about how I managed to be one of the lucky few that get to do for money what they’d probably be doing anyway: studying things that fascinate me. I work in neuroimaging, and in the midst of all the technical tom-foolery and undeniable hype there’s genuine nuggets of the weird, the wonderful and the fantastically enigmatic. One phenomenon that’s always a crowd-pleaser is split-brain surgery. A method of last resort for ‘refractory’ epilepsy which won’t respond to treatment, the corpus callosotomy procedure involves severing – partially or even completely - the main white matter super-highway between the brain’s two hemispheres in the hope of preventing the spread of seizure activity. The thing that fascinates neuroscientists and the lay public alike is the dissociation between behaviors that appear to be handled by one side of the brain versus the other. Today focus is: if it is possible that your one hand may not know what your other hand is doing, what happens when you ask them to explain themselves? Michael Gazzaniga is particularly associated with characterising split-brain phenomena, and in an enlightening experiment he and his co-workers went some way to exploring that question. 

Segregation of visual information

To begin with – to satisfy the good science-angel over my right shoulder - I have to acknowledge that for the sack of brevity and clarity I’m going glossing over subtleties. I’ll be adopting – appropriately enough given my theme – a story telling voice where bits of the brain ‘control’ behaviors and interpret information, ignoring the complexities of what that might mean. That said, before I get into the nitty-gritty of the experiment, there are a couple of background facts to consider. Have a look at the picture above and ignore all the labels: for our purposes they’re unimportant. Consider only the green and the purple. They indicate the left and right visual fields, and the path that the information takes to the visual cortex at the back of the brain. Notice that for each eye, the green purple split is half-and-half at the eyes, but one or the other at the visual cortex. What this depicts is the way that left half of the visual field of each eye is processed by the right side of the brain, and the right side of the visual field by the left hemisphere. You have a similar cross over in primary motor ( ‘movement’) processing too, but thankfully easier to explain: the left (mainly) controls the right, the right (mainly) controls the left. The point I’m laboring is this: each hemisphere has sensory input that only it receives, and an output system that only it mediates. In the context of split-brain patients, you sever the means of communication between the two hemispheres, interrupting the sharing of this side-dependent information.

Split Brain Experiment [1]

In the experiment depicted in the image above, Gazzaniga and co. [1] took advantage of this disconnect to display different images to split-brain patients in such a way that one picture was ‘seen’ only by the left hemisphere, one ‘seen’ only by the right. The patient was then asked to point to an image in front of them that was associated with the one they saw on the screen. The left hemisphere, seeing only the image of the chicken presented only to the right visual field, pointed with the right hand to the chicken’s foot. The right hemisphere, seeing only the image of a snowed-in house, pointed with the left hand to the shovel. The patient’s attention was then directed to the two images that they have pointed to, and asked why the left hand (the right hemisphere) is pointing to the shovel. Language - in most people -  is asymmetrically represented, and is left-lateralised in most people. Simplifying again, what this means is that - in general - if you ask a question of a split-brain patient, it’s thought to be the left hemisphere that answers you. And since it does not know why the left hand is pointing to the shovel, it does something very interesting. It makes up a neat causal story: the right hemisphere chose the shovel to clean out the chicken shed. It’s important to understand that the patient isn’t consciously lying: they are exhibiting a phenomenon called confabulation: 

confabulation (verb: confabulate) is a memory disturbance, defined as the production of fabricated, distorted or misinterpreted memories about oneself or the world, without the conscious intention to deceive.

Interesting, no? Quaint and safely clinical. But what if you and I were also subject to generating neat causal stories, and had just as little insight into the process that produced them as the split-brain patient does into the behavior of the two sides of their body? If psychology is sometimes thought of   as the science of the bleedingly obvious – with or without justice - my nomination for an exception to all that is the work of Daniel Kahneman and Amos Tversky. In a fruitful collaboration over several decades, they diligently explored the unconscious biases in the decision making and judgement of healthy, normal subjects. There’s an accessible – if a bit business orientated – popular summary in book form, but if I had to characterize their work in one sentence it would be the following: People are not natural statisticians,and don't realize it. For example, if we’re asked to make a judgement about the likelihood of an event, we might make a search of our memory for instances of the event happening before. We then use the ease with which we recall previous instances as a rule-of-thumb indication of the probability of the event happening again. We know, however, that our recall process – without our being aware – can be affected by a multitude of extraneous factors: mood, attention, prior beliefs, the way the question is asked and so on. But the bias is even more pernicious than that because the strategy itself is wrong: the true guide to the probability of an occurrence is not the times it did happen – even if we remember them correctly - but all the times it could but did not. 

xkcd

Littlewood’s Law is a back-of-the-envelope calculation meant to put million-to-one ‘miracles’ in their proper context. For the sake of argument, we’ll construe an ‘event’ – which can be exceptional or not - to occur each second, and then suggest that your average person is awake for about eight hours a day. That means that your average Joe should expect to experience million-to-one, seemingly miraculous goings on at a frequency of about once a month.  Lest you think this is all very well but not important, consider an example cited by Kahneman and Tversky to demonstrate the real-world significance of our propensity to see significance in the patterns we think we see:

“During the extensive rocket bombing in World War II, it was generally believed that the bombing could not be random because a map of the hits revealed conspicuous gaps. Some suspected that German spies were located in the unharmed areas. A careful statistical analysis revealed that the distribution of hits was typical of a random process – and typical as well in evoking a strong impression that it was not random.”

In this case, statistical due diligence was done: but consider the material outlay and consequences that might have ensued if the decision had been to root out the fictitious Nazi Spies. The really crucial point here, and the big difference with the split-brain patients is that in the patients’ case there actually was a cause: the experimenter’s choice of images. The patient’s mistake was to misattribute the cause to the wrong thing: the left-hemisphere’s reading of the right-hemisphere’s choice. But in the universal difficulty in considering all the things that that didn’t happen in the context of a truly large number of events, we don’t just misattribute causes: we posit them where none exists.

 I believe nothing of my own that I have ever written

– Charles Fort

At this point, I could score an easy point and liken this bias to the attachment of religious significance to events that are of personal significance. Indeed, I’ve treated something like that theme before. Or I could draw a comparison between this psychological preference for meaningful, causal stories to the wider human need for meaning in general. But I’d rather consider Charles Fort, and his parable of the rain of periwinkles and the story of Mad St.Fishmonger. Fort was a chronicler of weird, ‘unexplainable’ events and a positer of non-mainstream theories – such as the Super-Sargasso Sea dimension were all lost things end up – that he may or may not have been serious about (see quote, above). It is clear that he was concerned that positivist scientism could seek explain away and conventionalize truly Weird Shit, and end up providing ‘explanations’ that are just as fantastic in the process. For example, he recounts an alleged rain of fish in Worcester in 1881. Satirizing skeptics and their dogmatic belief that miracles cannot happen, he characterizes the only two explanation open to them. Either a strangely selective hurricane that could deposit only fish but not water nor seaweed or pebbles happened along. Or else, a hugely industrious and preternaturally stealthy fishmonger went to the expense and trouble of pulling a massive prank, without being seen or helped. 

There are extraordinary occurrences and conventionalization cloaks them, and the more commonplace the cloakery, the more satisfactory. Periwinkles appear upon a tract of land, through which there is a road. A fishmonger did it. 

– Charles Fort, Lo!

Weird shit happens. Not only should we be careful about explaining it away, but we should bear in mind that - sometimes - there’s nothing to be explained.

Gravure de pluie de poissons

[1] Gazzaniga, M.S. (1998). The Split Brain Revisited. Scientific American 279, 1, 35-39.

 

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