Psychology of Mirrors

Jack Dikian

October 2003

ABSTRACT

Why do Mirrors reverse left and right but not up and down?

Introduction

Kids spent hours puzzling over the fact that their mirror images are swapped left and right but not up and down and it seems that there's much about mirrors that we may not understand.

One of the most intriguing objects invented by man is the mirror. It is closely connected to our own consciousness, reflecting both reality and illusion and proving us with a tool for self-contemplation. The mere presence of a mirror in a room changes our social behaviour because it seems to make us more self-aware. Unlike other very early inventions such as the wheel, people still find it difficult to understand how mirrors work.

Dr Marco Bertamini, from the University’s School of Psychology, conducted a number of experiments involving mirrors. He said: “People tend not to understand that the location of the viewer matters in terms of what is visible in a mirror. See the “Venus Effect”.

When participants were asked to estimate the image size of their head as it appears on the surface of the mirror. They estimated that it would be similar to their physical head. However, participants based their answer on the image they saw inside the mirror rather than on the image on the surface of it. They failed to recognise that the image on the surface of the mirror is half the size of the observer because a mirror is always halfway between the observer and the image that appears inside the mirror.

Researchers have shown that mirrors can affect human behavior, often in surprising and positive ways. People tested in a room with a mirror have been found to work harder, to be more helpful and to be less inclined to cheat, compared with control groups performing the same exercises in non mirrored settings. Reporting in the Journal of Personality and Social Psychology, C. Neil Macrae, Galen V. Bodenhausen and Alan B. Milne found that people in a room with a mirror were comparatively less likely to judge others based on social stereotypes about, for example, sex, race or religion.

“When people are made to be self-aware, they are likelier to stop and think about what they are doing,” Dr. Bodenhausen said. “A by-product of that awareness may be a shift away from acting on autopilot toward more desirable ways of behaving.” Physical self-reflection, in other words, encourages philosophical self-reflection, a crash course in the Socratic notion that you cannot know or appreciate others until you know yourself.

Other researchers have found that inactive women exercising face-to-face with their reflections walk away feeling less energized, less relaxed, and less good about themselves than women who work out without mirrors to gaze at. In the study, (study was published in the journal Health Psychology) Kathleen A. Martin Ginis, an associate professor of kinesiology at McMaster University in Ontario, Canada, analysed the behavior of 58 college students after they spent 20 minutes on a stationary bicycle while wearing loose-fitting shorts, a T-shirt and running shoes. She says that the team was surprised to find that even women who were happy with their bodies were affected by the mirrors. "We thought that the effects would be strongest in women with the worst body image," she says, "but body image didn't matter."

The Left and Right Problem

Standing in front of a mirror and holding up your left hand. The person standing in the mirror holds up their right hand. It seems the mirror reverses left and right. It does not, however, reverse up and down.

The relative position from which you look in the mirror can make it seem like left and right are reversed. If for example, a person was standing above and behind the mirror, they, would describe you as lifting an arm near the right edge of the mirror because, they are standing opposite of you just like the mirror.

The mirror reverse is actually front-back. If you are heading north your image is heading south. Whilst we intuitively accept that left means left and right means right, in actual fact left and right are slippery concepts and hard to define. We need to know other things about an object before we can determine its right and left. For example, if handed a blob-like object and asked which side is its right side, we may not be able to determine that. It seems that we also need to know its top and front before we can identify its right side.

So, the three directions, top, front, and right are mutually perpendicular and it turns out that if we know two of them, then we can determine the third. For a person, a car, an animal, etc, the top and the front are unambiguous and intuitive - we use them to determine which side is the right side.

if we stand in front of the mirror and point at the mirror, then our reflection points in the opposite direction — the mirror image points back at us. In other words, the mirror reverses front and back. Our brain does not have to do any work to calculate the top and front sides of our reflected image. It uses them to calculate our reflection’s right side. More specifically the reflection’s up-down points in the same direction as ours, but the mirror image front-back points in the opposite direction. We point into the mirror and the reflected image in points out. Consequently, if top-down and in-out are accounted for, what remains for the brain is to cross left and right and we perceive the mirror reversing left and right.

Further Reading:

The Left Hand of the Electron, by Isaac Asimov, contains a very readable discussion of handedness and mirrors in physics.

The Ambidextrous Universe, by Martin Gardener is another book that covers this subject.

The Feynman Lectures Volume 1 contains a chapter Symmetry in Physical Laws that deals with what we mean by left and right, and how we might go about instructing a Martian on these concepts.

Key words: Mirrors, psychology of mirrors, human behaviour, self-image, self image, psychology, self-aware, self-awareness, self-reflection.