Face-Specific Perceptual Distortions Reveal A View- and Orientation-Independent Face Template

Abstract

The spatial coordinate system in which a stimulus representation is embedded is known as its reference frame. Every visual representation has a reference frame [1], and the visual system uses a variety of reference frames to efficiently code visual information [e.g., 1, 2, 3-5]. The representation of faces in early stages of visual processing depends on retino-centered reference frames, but little is known about the reference frames that code the high-level representations used to make judgements about faces. Here we focus on a rare and striking disorder of face perception -hemi-prosopometamorphopsia (hemi-PMO) -to investigate these reference frames. Following a left splenium lesion, Patient A.D. perceives features on the right side of faces as if they had melted. The same features were distorted when faces were presented in either visual field, at different in-depth rotations, and at different picture-plane orientations including upside-down. A.D.'s results indicate faces are aligned to a view-and orientation-independent face template encoded in a face-centered reference frame, that these face-centered representations are present in both the left and right hemisphere, and that the representations of the left and right halves of a face are dissociable. KeywordsFace processing; Hemi-Prosopometamorphopsia; View-independent face representation; Splenium; Highlights• After a left splenium lesion, A.D. sees features in right face halves as distorted • A.D.'s distortions affect the same features under all stimulus manipulations tested • Face processing involves a view-and orientation-independent face template • The face vertical midline is an important representational divide in face processing In BriefAfter a left splenium lesion, patient A.D. sees the right halves of faces as melting. Almeida et al.show that the distortion affects the same features regardless of position, rotation in-depth, or in-plane inversion, indicating that faces are encoded in a view-and orientation independent manner.

Vision: Face-Centered Representations in the Brain

“…To integrate these split-half representations and produce a bilateral perception, A.D.'s hemispheres communicate via a lesioned corpus callosum. Almeida et al's [1] results suggest that the impaired architecture does construct a bilateral representation of the two face halves in the left and right pathways (see also [6]). Whether each comprises a face-centered distortion of the right face half remains an open question.…”

“…A key challenge remains to understand the format of these lower-dimensional representations and their contents, both in the brain and its models. In this issue of Current Biology, Almeida et al [1] address the challenge in a study of patient A.D., who experiences a sudden and systematic perceptual distortion of the right side of faces -the right half of a face appears 'melted', in a similar manner to the melted clock on Dali's famous painting -as a result of a left splenium lesion of his corpus callosum that hinders the exchange of information between the two hemispheres.…”

“…Almeida et al [1] used this rare condition to adjudicate between three frames of reference as possible formats of A.D.'s face representations. A retino-centered format would represent the visual field, with A.D.'s perceptual distortions located only to the right side of his fixations.…”

“…Perceived distortions would follow any rotation of the face, in the two-dimensional image plane or in three-dimensional depth. For example, a face rotated clockwise in the image plane would be perceived with a distortion on the right side of the face itself, irrespective of the rotation angle of the face (see Figure 1 in Almeida et al [1]). This reasoning motivated the experimental work of Almeida et al [1], which provided clear support for the face-centered format.…”

“…For example, a face rotated clockwise in the image plane would be perceived with a distortion on the right side of the face itself, irrespective of the rotation angle of the face (see Figure 1 in Almeida et al [1]). This reasoning motivated the experimental work of Almeida et al [1], which provided clear support for the face-centered format. That is, perceptual distortions on the right side of the face persisted even when an image was projected in the left and right visual fields either as full or as left and right split-halves faces, or rotated in the two-dimensional image plane or in three-dimensional depth to reveal only the profile or three-quarter view.…”