The new peer-reviewed study, published in the Journal of Experimental Psychology, was based on two trials.
In all cases those participants exposed to images of blondes recorded the lowest scores.
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...That they were spending real money researching the subject. Personally I think their results are in error, though. The reduced intelligence is related to perception, yes, but probably has more to do with a lack of blood flow to the brain (as it goes elsewhere) or increased testosterone levels. That's just my wild hunch on the subject. I doubt very much that it has anything to do with thinking.