Part of what helps you to identify friends and relatives is information about their body. You recognize their height, body shape, and even their manner of walking. In fact, all of that may help you to know who you are looking at before the person is close enough to really see his or her face.

An interesting paper in the November, 2013 issue of Psychological Science by Allyson Rice, Jonathon Phillips, Vaidehi Natu, Xiaobo An, and Alice O’Toole demonstrates that people use information about the body to identify people, but they are not aware that they are doing so.

In these studies, participants saw pairs of pictures drawn from a large database. Participants had to identify whether the pair of pictures showed the same person or different people. The pictures used in the study were carefully selected so that this task was quite difficult. Many of the pictures of the same person were rather dissimilar, while many of the pictures of different people were similar to each other. As a result, face information alone was not helpful in determining whether the people in each pair were similar.

When participants were given the full pictures, they were reasonably accurate in making the judgments of which pictures were the same or different. Some participants were shown only the faces from the pictures. This group was not good at all at distinguishing the same and different pairs. A third group saw only the bodies with the faces covered by an oval. This group was about as accurate at identifying the pictures as the group who saw the full pictures.

So far, this probably doesn’t seem so surprising.

In another study, participants were given the full pictures to judge. Afterward, they were asked about a variety of facial and bodily features, and were asked how much they used this information to make the judgments. Participants performed well in this study, suggesting that they had to be using information about the body, but their ratings suggested they believed that they were focused on the nose, face shape, ears, mouth, eye shape and eyebrows, but not on properties like the hair length, height, shoulders, and neck.

These ratings suggest that people are mistaken. That is, when people see just the face information, they are not able to distinguish between the pictures of the same people and pictures of different people. The body shape information is important, yet people do not report using it.

A final study demonstrated that people really were reporting the information they used to make judgments incorrectly. In this study, participants saw full pictures. They viewed the picture pairs while their eyes were being tracked. Eye tracking enables researchers to monitor what people are looking at on a moment-by-moment basis. The technique is effective, because you clear vision for only a small area (about the size of your thumbnail at arm’s length). So, your eyes are constantly in motion to create a clear image of what you are seeing.

In this eye tracking study, some of the pairs of pictures were ones in which face information could be used to make reasonably accurate judgments. Other pairs required body information to be used. When the face information was helpful for making judgments, people looked at it quite a bit. When the face information was not helpful for making judgments, then people focused more on areas of the body that would help them to determine whether the two people were the same.

What does this mean?

First of all, your visual system is smart. It does a good job of figuring out the information you need to make judgments.

Second, you do not have complete access to all of what your visual system is doing. Even though you shift your from the face to the body when body information will help you to recognize a person, you still think that you are focused on the person’s face. This is another great example of how your conscious experience of what you are doing is not an accurate portrayal of what you are actually doing.

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