Computer Vision (4)

We humans have 5 different kinds of senses; touch, smell, sight, hearing and taste (correct me if I missed out something). We have one tongue, two eyes, two ears and two nostrils and of course skin for the sense of touch (skin is a special case I will come to it later). Ever wondered why we don’t have two tongues? Does this number two or one make any sense to our senses? Let me illustrate their significance with some examples.

1. You can pick up a pen that is lying in front of you at one go. (Vision)
2. When someone calls you from your left you immediately turn towards your left instead of searching for the voice all around you. (perception of sound)
3. And of course fragrance definitely attracts you towards it. (sense of smell)

Each of these senses is highly developed in the order mentioned. As you can observe in these examples, when you have a pair of sensors they answer the question WHERE? WHERE is the object, WHERE is the sound and WHERE the smell is coming from? You don’t have two tongues because you know that to taste something you have to place it on your tongue and can’t do it wirelessly. WHERE, is something that becomes obvious in this case. The final sense is touch and when it comes to skin there is nothing like one and two and it covers our entire body. But we all know that it is sufficient to touch us at one place to feel it, rater than at two. You have to make a contact to have a sense of touch which eliminates the need to answer the question WHERE?

Just the presence of two senses needn’t always guarantee the answer WHERE, it is their placement that gives it an extra edge. In general there needs to be some common signal that passes through both of the same kind of sense. Light is a high frequency wave and cannot bend along the corners. I mean you can’t light up your room and go outside behind the room wall to read something, while this is not the case with sound or smell. So irrespective of where on your head the two ears or nostrils are placed, common signals will definitely reach them but you can’t place one eye at the front and one behind your face. Light can’t bend so you don’t get any overlap or in other words a common signal in both the eyes. We humans have both our eyes on the front of our face, so it’s very easy to get common signals. Want to experiment? Fix the position of your face and close one of your eyes, say the left one first. Remember the region that your right eye is seeing. Now close your right eye and open the left and compare the two regions. Most of the region that one of your eyes sees will also be seen by the other, which is the common region. The right eye will not be able to see the left most portion of the region seen by the left eye and vice versa. It is in this common region that we perceive depth. How?, I will explain it in detail later, for now you just need to remember that “2 sensors == 3D perception”.