New York, Aug 17 (IANS): People suffering from a rare brain disorder, when they look at someone, they see distortions to the same half of a person's face, regardless of how the face is viewed. Researchers have now decoded why this happen.

People who have a rare condition known as hemi-prosopometamophosia (hemi-PMO) makes it discomforting for them to look at faces.

According to a new study published in Current Biology, the results demonstrated that our visual system standardised all the faces we perceive using the same process so they can be better compared to faces we have seen before, like a face recognition system.

"Every time we see a face, the brain adjusts our representation of that face so its size, viewpoint, and orientation is matched to faces stored in memory, just like computer face recognition systems such as those used by Facebook and Google," explains study co-author Brad Duchaine, a professor of psychological and brain sciences at Dartmouth College in the US.

Hemi-PMO is a rare disorder that may occur after brain damage.

When a person with this condition looks at a face, facial features on one side of the face appear distorted.

The existence of hemi-PMO suggests the two halves of the face are processed separately.

The current study focused on a right-handed man in his early sixties with hemi-PMO whose symptoms have persisted for years.

He looked in the mirror at his own face and noticed that the right side of his reflection was also distorted.

The study involved two experiments. In the first, the patient was presented with images of human faces and non-face images such as objects, houses and cars, and asked to report on distortions.

For 17 of the 20 faces, he saw distortions.

The distortions were always on the right side of the face and facial features usually appeared to drooped.

For the second part of the study, the patient reported on distortions that he saw in 15 different faces that were presented in a variety of ways: in the left and right visual field, at different in-depth rotations, and at four picture plane rotations.

Regardless of how the faces were presented, the patient continued to report that the distortions affected the same facial features.

"The results demonstrate that our visual system standardizes all the faces we perceive using the same process so they can be better compared to faces we have seen before," the authors wrote.