"If your IQ is somewhere around 60 then you are probably a carrot'', according to a British spokesman for high-IQ club Mensa.
IQ's in the news at the moment thanks to a paper called Fractionating Human Intelligence from Canadian psychologists Adam Hampshire and colleagues. Some say it'debunks the IQ myth' - but does it?
The study started out with a huge online IQ test...
Behavioral data were collected via the Internet between September and December 2010. The experiment URL was originally advertised in a New Scientist feature, on the Discovery Channel web site, in the Daily Telegraph, and on social networking web sites including Facebook and Twitter.
The test involved 12 different cognitive tasks, based on the usual IQ test kind of things, and they got a huge 45,000 usable responses.
However, the main part of the study used functional MRI (fMRI) to measure brain activity caused by each of the 12 tasks. There were only 16 volunteers in the brain scan study, which is pretty small.
The key finding was that although each of the 12 tasks made a different pattern of brain regions light up, there were two main components of this: one lit up mostly in response to tasks requiring short-term memory, and the other was associated with reasoning and logic:
(EDIT: Picture corrected, oops.)
They did various other analyses that confirmed this, and they also found evidence for a third network responsible for language (verbal) skill.
Finally, the killer conclusion was that there was
no reason to introduce the imfamous 'g factor' - a number representing general intelligence affecting performance on all tasks.
Although there was a 'g factor' statistically, it was explained by the fact that tasks required both the memory and the logic networks (although to different degrees).
g is the most controversial aspect of IQ testing, because if it exists, that means that some people are just smarter than others across the board - not just better at a particular kind of thing. So has this study killed g?
Well, not by itself. There's a huge literature on IQ and g, going back almost 100 years. This stuff is not based on brain imaging, but just on IQ test scores, and it's a complex topic. I don't think one brain study with 16 people can really overturn that, although it does lend weight to the anti-g camp who have been arguing against g for decades.
There's a sense, though, in which it doesn't matter. If all tasks require both memory and reasoning (and all did in this study), then the sum of someone's memory and reasoning ability is in effect a g score, because it will affect performance in all tasks.
If so, it's academic whether this g score is 'really' monolithic or not. Imagine that in order to be good at basketball, you need to be both tall, and agile. In that case you could measure someone's basketball aptitude, even though it's not really one single 'thing'...
Hampshire, A., Highfield, R., Parkin, B., and Owen, A. (2012). Fractionating Human Intelligence Neuron, 76 (6), 1225-1237 DOI: 10.1016/j.neuron.2012.06.022