Conversation Topics: Mirror Image
How can two people witness the same event but swear that two different things happened?

The reason people have different recollections of what happened -- even if they stood side by side and witnessed the same thing -- is that our brains process and interpret what our eyes see. In other words, we do not see what is actually there. Instead, our brains are rapidly interpreting it to make sense out of it for us. When we see an image on the computer screen, for example, we don't see an image on the screen -- we see a picture with recognizable objects -- trees, houses, people, etc.

Our eyes are like cameras that are constantly feeding impressions of color and light intensity to our brains. This flood of data is far more than the brain can handle, so it does two things. First, it limits what it processes; this is what we commonly call the things we 'focus' on. While we are aware of movement in our 'peripheral' vision, our brains are busy recognizing shapes only in the area where we focus. The second aspect is this recognition process. We are constantly looking for shapes, sizes, and colors in the stream of impulses coming form our eyes so that we can identify in the image things that we know. What's the first thing we want to do when we find something new? We instinctually want to pick it up and turn it over and over in our hands as we examine it --- what we really are doing is trying to get a good mental image of it so that we will recognize it in the future from many different angles.

Thus, when we're asked to reconstruct what happened, what we remember happening depends on what aspect we saw, what we recognized in what we saw. The "truth" gets even murkier because most people will subconsciously fill in gaps in what they saw with what they would expect to have happened.

Here's a nifty experiment in visual perception where you can demonstrate the brain's processing at work. When you look in the mirror, your image is backwards, right? That's what we commonly call the "mirror image." If we touch our left ear, the image in the mirror touches the ear on our left --- but if we imagine that we were that person in the mirror, we would be touching our right ear. But why is the image reversed left to right and not top to bottom?

To begin with, the image is reversed because of the angle between our eyes and the light reflecting off the mirror. When we look to the right, we see the image of the right side of our face. When we look to the left, we see the image of the left side of our face. This creates the impression that the image is reversed because normally, if we look to the right, we would see the left side of a person's face. (It's interesting to note that if you look directly into the mirror, the point directly in front of our eyes is not reversed. It is also relevant to note that if the image we saw did not contain objects that we recognized as reversed (for example, our image, words, etc.), we would not know that the image we were looking at was reversed.)

Understanding this, you might be led to speculate that the image in the mirror is reversed left to right because our eyes are aligned on a horizontal plane. No such luck. If you close one eye, the image is still reversed left to right.

Nor does the reversal of the image have anything to do with the orientation of the mirror. If you rotate the mirror, nothing changes -- it still reverses the image left to right. Same thing is true if you lay down so that your eyes are stacked one on top the other -- still no change.

However, despite all of this verification that a mirror reverses an image left to right, the truth is that the mirror doesn't reverse the image at all. It's all in our heads: we perceive the image in the mirror as being reversed left to right. In truth, you could easily say the image is reversed top to bottom.

Top to bottom? We say the image is reversed left to right because if that really was a person on the other side of the mirror, when I touch my left ear they would be touching their right. We draw that conclusion because we imagine the mirror is a clear glass and that we can walk around and standing behind it. My reflection is still touching the ear on my left side, but that ear is his right ear.

Now imagine that instead of walking around the mirror, you climbed over it and hung by your ankles facing back towards you from the other side.Your left and the left of you while hanging upside down on the other side are still on the same side. Now the only problem is that the upside down you and the image in the mirror is reversed top to bottom -- not left to right..

Hard to picture? Try taking a piece of paper and writing 'top,' 'bottom,' 'left,' and 'right' on the appropriate edges of the paper. Write 'mirror' in the center. Flip the paper over and write the opposites ('left" where you can see you wrote 'right' on the other side, 'top' for 'bottom,' etc.). Write 'me' in the center. Now hold the paper to your chest with the side marked 'me' showing,. The 'left' edge should correspond to your left arm and the 'top' edge to your head.

Let's simulate you walking around behind the mirror and facing yourself. With your right hand, reach around the front side of the paper and grab the edge marked 'left.' Extend your arm out in front of you with the 'me' side now facing you. This is how you in fact appear to others: our left side is on their right side. However, in the mirror, remember, when you touch your left ear, the image touched its right ear. To make that happen, you need to flip the paper over left-to-right. Now the 'left' sides are on the same side.

Now let's try reversing the image 'top to bottom.' Place the paper on your chest again, 'me' side out, just as we did before. This time, grab the 'top' edge with your right hand and flip the page over top to bottom in front of us so that the 'me' side is now facing us. We find the left edge of the paper is on our left side, just like in the mirror. But now, the top and bottom are reversed. That's easy to fix, just flip the paper over again, top to bottom. Thus, we can imagine how to create the image in the mirror by either reversing what we would expect to see 'side to side' or 'top to bottom.'

Faced with that dilemma that the image is somehow transformed, the brain, not the eye, interprets the image in the mirror as reversed side to side because people generally have their feet on the ground, head in the air, are symmetrical side to side, and their hair dangles downward when they are upside down. Hence, from the visual information from our eyes, our minds form a conclusion, and we're read to swear in court that the mirror image is reversed left to right even though it could just as easily be reversed top to bottom..

The mirror is just one way of showing that we interpret everything that we see around us. And that's why two people can witness the same car accident and come away swearing that two different things happened.<

Updated September 30, 2003 - go to our home or life advice page