The paper is likely off limits to most people, but thanks to having wonderful university access to research journals, I bring to you a paragraph delivering the real meat of the research:

There must, however, be some degree of homogeneity among the faces for the outliers to stand out and for the effect to occur. The distortion effect, therefore, seems to depend on the outlying dimensions among the images in the set, and these dimen- sions do not seem to be limited to facial features or configurations. For example, if a photograph is brightly lit compared to the others, then it appears overexposed. Presumably, then, the effect relies on the same contrastive mechanism that gives rise to shape-contrast effects. Suzuki and Cavanagh (1998), for example, demonstrated that a briefly flashed line distorts a circle into an ellipse that appears elongated orthogo- nally to the line orientation. Owing to the multidimensional nature of the faces in our flashed face distortion effect, the resulting distortion is not on any single dimension, but on every dimension along which the face images vary. In contrast, face distortion after effects commonly result from prolonged exposure to one face with a single exaggerated dimension defined by the experimenter, such as the distance between the eyes.

Tangen J M, Murphy S C, Thompson M B, 2011, "Flashed face distortion effect: Grotesque faces from relative spaces" Perception 40(5) 628 – 630

Edit: Formatting.