“Not only faces”: specialized visual representation of human hands revealed by adaptation

Classical neurophysiological studies demonstrated that the monkey brain is
equipped with neurons selectively representing the visual shape of the
primate hand. Neuroimaging in humans provided data suggesting that a
similar representation can be found in humans. Here, we investigated
selectivity of hand representation in humans by means of the visual
adaptation technique. Results showed that participants’ judgment of
human-likeness of a visual probe representing a human hand was
specifically reduced by a visual adaptation procedure when using a human
hand adaptor but not when using an anthropoid robotic hand or a
non-primate animal paw adaptor. Instead, human-likeness of the anthropoid
robotic hand was affected by both human and robotic adaptors. No effect
was found when using a non-primate animal paw as adaptor or probe. These
results support the existence of specific neural mechanisms encoding human
hand in the human’s visual system.