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Is the right brain hemisphere more analog and Bayesian?

Oliver Schultheiss writes:

I recently commented one of your posts (I forgot which one) with a reference to evidence suggesting that the right brain hemisphere may be in a better position to handle numbers and probabilistic predictions. Yesterday I came across the attached paper by Filipowicz, Anderson, & Danckert (2016) that may be of some interest to you. It suggests at least 2 things:

First, there is actually a lot more research than I knew about that shows that the right hemisphere is better at intuitive statistics. If parts of it are missing, people have severe problems adapting to probability (changes) and making the right guesses. You don’t get that when the left hemisphere is compromised. In fact, the right hemisphere appears to work like a real Bayesian, with prior beliefs and updating as the data come in (s. Figures 7, 8, and 9). In general, it adapts in a graded, analog fashion to incoming information. This in stark contrast to the left hemisphere, which of course is also capable of predicting what happens next, but does so in a much more digital, either/or, black/white manner (or should I say: significant/non-significant manner?). The approach to statistics that you espouse on your blog and in your books (e.g., Regression & other stories) is decidedly one that is more closely aligned to how the right hemisphere deals with probability and uncertainty than the approach of the left hemisphere.

Second, the authors provide a wonderful demonstration of how we deal behaviorally with probability and uncertainty using the game Plinko (for a demo please see here: https://osf.io/dwkie/ — but you need PsychPy to run it). It’s illustrated in Figure 7 and requires players to first state their prior beliefs about how a ball will fall through a grid of pins and how often it will end up in a variety of bins underneath the grid. You can then study how people update their beliefs as the data from the first test runs come in. The beauty of this example is, of course, that the actual probability distribution that emerges over time as close to a Gaussian. But that’s not what everybody expects. Some peoples’ priors are bimodal, some believe in a rather jagged kind of distribution, and I guess other priors are possible too. This might be a nice teaching tool for the kind of intuitive Bayesianism our right hemisphere engages in (and which vanishes or becomes distorted after right-hemisphere damage).

Perhaps you’ve already seen either the paper or the Plinko game before. I was very impressed by this review paper, because I hadn’t been aware how much is already known about hemispheric differences in statistical reasoning.

I know nothing about this! But it seems interesting, so I’ll share it. I hadn’t thought about Regression and Other Stories as being a right-brain-style book!

14 Comments

  1. Paul Hayes says:

    This in stark contrast to the left hemisphere, which of course is also capable of predicting what happens next, but does so in a much more digital, either/or, black/white manner (or should I say: significant/non-significant manner?).

    Just say it does so in a sinister manner.

  2. Adede says:

    I thought the whole left/right brain thing was bunk? Then again, the replication crisis has been so severe that I reflexively disbelieve anything I was taught in school or read in the news.

    • Alex says:

      The right/left thing is mostly bunk, and given that the vast majority of people have intact communication between the hemispheres it is bunk for practical purposes. But there are some differences in what the two hemispheres do or how they do it.

  3. Oliver C. Schultheiss says:

    Some of it was bunk, particularly the wholesale characterizations of the left hemisphere as the language and analytic hemisphere and the right as the nonverbal and emotional one. But the neuropsychology and neurology literature shows that there ARE some critical differences between the hemispheres in terms of attentional systems, targeted/sequenced manual control, representation of body schema, and the like. It’s actually quite fascinating if you’re willing to deal with to deal with the fact that things are a bit more comllex than simple either/or dichotomies. As Paul Hayes nicely put it, that would be the sinister way of the sinistral hemisphere…

  4. Matt Skaggs says:

    What’s bunk?

    Perhaps interpretations by psychologists and representations in the media.

    Certainly not the neuroscience part. By the time Michael Corballis wrote “The Lopsided Ape” in 1991, there was already a rich literature on the differences between the two brain hemispheres. Since then, the functional studies performed on brain-damaged subjects have been supplemented by sophisticated measurements of brain activity.

  5. Anoneuoid says:

    Makes sense. The bayesian right brain started out as a “voice of god” ordering the “NHST” left brain what to do via auditory hallucinations. We are still dealing with the remnants today.
    https://en.m.wikipedia.org/wiki/Bicameralism_(psychology)

    That explains why NHST users cannot give any rational explanation for their analytic decisions and do not respond to any reason. The right brain has accumulated so much evidence that rewards come from using NHST that the user cannot stop using it.

    • Matt Skaggs says:

      “That explains why NHST users cannot give any rational explanation for their analytic decisions and do not respond to any reason. The right brain has accumulated so much evidence that rewards come from using NHST that the user cannot stop using it.”

      Ooh, brain dualism bunk in real time!

  6. oncodoc says:

    I wonder if the left/right differences reflect training or some innate differences. I hung out with some handball players in my youth. They train to achieve equal skill with either hand. Jimmie Hendrix was a righty who was self taught and as a child picked up the guitar with the “wrong” hand to become an outstanding virtuoso playing left handed. Many left handed pianists become righties at the keyboard except when they play Chopin who was a lefty. Mickey Mantle used his right hand for most things, but his father was a lefty pitcher, and the Mickster learned to bat lefty. Mickey was excellent from both sides. My daughter is a printmaker who engraves lefty because it makes it easier to do the reverse image that way. I am willing to believe that there is some intrinsic difference between the hemispheres with Broca’s area the big one, but lofs of things can be achieved by training. And training begins very early in life.

    • A study of left-handed couples who adopt new borns … :-)

    • Wondering... says:

      For decades I have played the violin and piano. Violin is a very left handed activity (the right hand holds the bow), so I suppose my left hand is very dextrous. But when I play the piano I am far more comfortable with my right hand than my left hand.
      Perhaps without my violin playing my left hand on the piano would be truly atrocious?

    • Andrew Wilson says:

      When I was in high school, or perhaps it was middle school, I recall learning how to write with my left hand (I’m right handed). I recall starting this when I was writing prepositional phrases for homework, aboard, about, after, against, along, amid,…

      My right hand got tired, and we weren’t graded on penmanship, so I learned how to write with my left hand. My right hand is still dominant, but I now use my left hand as much as I can: computer mouse, knife and fork, credit card signatures.

      It’s useful, though moreso in school, filling in scantron bubbles for a test, or writing multipage essay tests by hand.

    • Oliver C. Schultheiss says:

      Well, here’s more nurture for you (literally!): handedness appears to be associated with breastfeeding duration according to a recent meta-analysis:

      https://www.tandfonline.com/doi/full/10.1080/1357650X.2018.1555254

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