Estimation and representation of head size (people overestimate the size of their head - evidence starting from the 15th century).

The head is a special part of our body since we do not see it directly. Four experiments were conducted to verify what healthy people know about the size of their head. As a control, we used the accuracy in estimating other people's heads (in all the experiments) and the estimation of the size of another part of the body, the hand (in Experiment 4). Results showed that people overestimate their own head size compared to its actual size when visual information is not provided (Experiments 1-4). They also overestimate their head size compared to the heads of others whether viewed directly (Experiment 1) or from memory (Experiment 2). Overestimation with respect to the actual size is reduced when visual information is provided (Experiments 1 and 4) and when proprioception is (presumably) increased by wearing a headband (Experiment 3). Overestimation with respect to actual size is not found for hands (Experiment 4). In the final study evidence emerged of head size overestimation in self-portraits as compared to portraits of others.