The chances are, you're not as big-headed as you think. I don't mean you're modest. I mean, literally, that the physical size of your head is smaller than you think it is.
I say this because a team of psychologists led by Ivana Bianchi have shown that students overestimated the size of their own heads, but not other people's, by between 30 and 42 per cent, on average. Other people's head sizes were also overestimated if their size was judged from memory - although the overestimation was not as large as when the students' judged their own heads. Similar results were found whether the students indicated head size by drawing an outline on paper or by demonstrating size with a tape measure.
As a comparison task, students estimated the size of their own and other people's hands. If anything, this led to underestimation.
The overestimation of head size was almost entirely removed when students made their estimates with the help of a mirror, and also if they wore a headband from the top of the head to the chin (thus providing proprioceptive feedback).
In a neat, final study, the researchers compared the size of heads in portraits and self-portraits dating from the fifteenth to twentieth century. Head size was bigger in the self-portraits.
The researchers don't really know why we overestimate our head size. The fact we can't see it directly no doubt has something to do with it. However, another possibility, according to Bianchi's team, is that thinking our heads are bigger than they really are is actually just another self-serving delusion - similar to the way most of us think we're cleverer and more attractive than is really the case.
Bianchi, I., Savardi, U., Bertamini, M. (2008). Estimation and representation of head size (people overestimate the size of their head – evidence starting from the 15th century). British Journal of Psychology DOI: 10.1348/000712608X304469
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