On the other side of the mean: The perception of dissimilarity in human faces

We created a 'face space' using a laser-scan representation of faces. In th is space, a caricature can be made by moving a face away from the average f ace, along the line connecting the particular face to the average face. Her e, we move the face along this line in the other direction, proceeding thro ugh the mean and 'out the other side'. This results in a face that is 'oppo site', in a computational sense, to the original Face. We morphed several f aces into their anti-faces and sampled the morph trajectory in five discret e steps. We then collected similarity ratings from human participants for a ll possible pairs of morphed faces to determine how the distances in the 'p hysical face space' related to the distances in the 'psychological face spa ce'. The data indicate that there is a perceptual discontinuity of face ide ntity as the face crosses over to the 'other side of the mean'. We consider these results in the context of face-space models of human face processing .