Thursday, August 9, 2012

Highly exceptional cognitive test scores versus exceptional performance

I was pondering the other day why the best performers such as Nobel prize winning physicists, best mathematicians, and so on, do have somewhat high, but not truly exceptionally high performance on the IQ test and similar tests, while some of the ultra high IQ individuals, or ultra exceptional childhood SAT solvers seem to be smart, but for the lack of other word, not really be that smart or wise or capable as the scores would suggest.

The on-going Olympics provides a clear analogy. The best sprinters will not be the best marathon runners; former have large fast versus slow fibres ratio and metabolism geared more towards anaerobic performance, whereas the latter have primarily slower fibres and metabolism geared towards aerobic performance. Past certain level of exceptional performance, there could be very little overlap between the exceptional performers in those two related, but different sports. Note that the best sprinters will still run marathons a fair bit better than average man, and best marathon runners will still sprint better than average man.

The brain is a fair bit more mysterious organ than the muscle, and we understand it very poorly, but it is the case that there are several well known variables that would represent a trade-off between different types of performance. For instance, glia to neuron ratio. Glia are the support cells that provide nutrition to neurons as well as remove the metabolism by-products of the neurons; furthermore glia have been recently found to be implicated in the memory.

Glia to neuron ratio should influence the cognitive performance, and it appears highly unlikely that the optimal ratio for the tests would precisely coincide with the optimal ratio for the insight making or the real world performance. There are many other such trade-offs within the brain. Hormonal levels, thickness of myelin shealths, short range vs long range connectivity, gray matter vs white matter... you can continue this list for pages.

The short term tests consisting of large number of disjointed questions which do not involve a significant body of learned knowledge (outside verbal, which represents a highly specialized brain region and very special type of learned knowledge) seem even more distant from insight making or long term work than sprint is different from a marathon race; I would expect even less of an overlap between exceptional performers on the criteria there. The relation may be more similar to that between grip strength and biathlon.

With regards to the childhood testing, it seems clear that exceptional childhood athletes at age 10 would have variations (Various hormonal dis-balances?) that are detrimental to the adult performance.

Note that none of this argument contradicts existence of correlations. Bulk of measured correlation comes from the values close to the mean, and it is the case that all the exceptional performers at age 20 were very good at age 10. Just not as good as the phenotypes which make use of the trade-offs.

edit: See also: Spearman's law of diminishing returns ; among the high IQ range, the correlation between different traits decreases. It is thus not surprising that at high IQ range, the correlation between the skills implicated in IQ test and skills implicated in, for example, theoretical physics, would decrease.


  1. You can also get results like this if anything else besides IQ matters. With a bell curve, going from 0 SD above the mean to 1 SD above the mean, IQ 115, shrinks your population by 2/3. Next SD by another 6/7ths, then 16/17ths. Each marginal IQ point can shrink the number of people who have it more rapidly than the marginal IQ helps. And in a small population you can't find people who are exceptional in other mostly independent traits.

    So if you select for a weighted combination of general intelligence, specialized mathematical ability, temperament, and luck (meaning their most fruitful topic was Nobel-worthy, they didn't get screwed over by the vagaries of timing and judging or an early death, experiments could be performed to confirm their result in time, etc) the top overall performers should not be at the very top of every individual contributing factor.

    The Terman study of high-IQ kids missed some future Nobelists "just slightly below the cutoff," because that group had similar IQ but was much larger.

    1. Indeed. What I proposition, however, predicts less overlap than the external factors you outlined would alone, just as there is less overlap between marathon runners and sprinters due to different slow vs fast muscle fibre ratios that are optimal for either sport.

      Note that while this is difficult to test directly on the performance due to small sample size, this is a deduction from what we know of muscle physiology. Likewise, we should be able deduce conclusions about transferability of exceptional mental abilities from what is known of brain physiology.

      Normally one could assume that the probability of, say, winning a Nobel prize in science would grow monotonously with the percentile on the performance test. I however expect that at some point the probability will start to decline, as the individuals at such level would have glia/neuron ratio (and other trade-offs) which are highly optimal for the tests.

      While the assumption of single dimensional 'general intelligence' is certainly useful, it is not physiologically nor neurologically plausible that it holds into the exceptional performance level.

      If you look at the geniuses, what is most striking is their ability to work really hard:

      Other striking difference is in some ill defined ability to, for example, come back to work knowing about a bug in some function that they wrote half a month ago and which was never tested - ability to run some sort of process in the background, which is entirely irrelevant to tests (if not actively harmful to the test performance). The 'computationally expensive insight out of the blue' capacity.