Is the human brain a computing device? i.e. Does it even make sense to compare a biological thing like a human brain with man-made computer?
For those who find the idea of comparing the human brain (which is purely biological in nature) with computers (that are purely man-made and dead matter) to be strange, it's worth spending some time to grasp the idea and rationale behind looking at the human brain as a “computing device”.
It's important to note that while doing this, we will ignore the self-awareness or consciousness part of it for multiple reasons including the fact that we don’t know really understand them in the first place!
Lets us start by considering things that both the human brain and computers can do.
1st example: Numerical Computation
The simplest one being numerical computation. Humans can compute 2+2 and also much more complex math and we have now created computers that can do that too (much faster than our brains can). We can remember things and computers can also do that, meaning there is some type of memory in the brain. So if you just focus on the task of computing 2+2, you realize that the numbers like 2, 0, -2, etc. and meaning of ‘+’ (let's call it “rules”) have to be somehow represented in both our brains and the computer. This is one simple example to illustrate that the brain is indeed a computing device.
2nd example: Image recognition
Now let's consider a slightly more complex example of identifying a chair when you see it with your eyes and when you feed that image or video to a computer. The human brain receives the visual signals from our eyes and very quickly classifies some of the characteristics of the object namely, color, shape, size, moving vs stationary, etc. With this observation, we can hypothesize that there has to be some classification mechanism in the brain for each characteristic. With the help of fMRI, we know that this hypothesis is true. As an example, we now know that damage to a specific region of the brain can cause color blindness. Now in order to focus on this ability of the human brain of being able to identify a chair, it makes sense to think about an infant who sees a chair for the first time and then try to hypothesize what the brain might be doing. If you do that, it becomes fairly obvious that the identification and ‘labeling’ of an object as a chair with its characteristics fundamentally depend on the idea of learning. Meaning observing what others are doing with that object, comparing it with other objects of different sizes, shapes, and color and then creating this mental model of the chair as an object that is inanimate and is used to sit.
Now note that each of these aspects including representation of each pixel in an image in terms of its color (including the contrast and brightness) etc. can be done in computers. We can also write ‘rules’ so that computers can identify an object like a chair. The way you would do that is that you would write rules that take a collection of the pixels in an image and classify the color, shape, etc. all the way to building an entire model for a chair. So this complex example also illustrates that the brain is indeed a computing device.
Image recognition by today’s computers
While we are at it, let's take the example of recognizing a chair to get an appreciation of why it's so hard for a computer to do this?
Given that today’s computers are logic/rule-based with some memory, in order to recognize an object like a chair, each image will need to be broken down into millions of pixels to have enough granularity (and information’). And then write rules so that the computer can match the set of pixels to that of an image of a chair. When you try to do that, you realize fairly quickly that there will need a write billions or trillions of “rules” to distinguish different objects because the permutations and combinations of all the clusters of pixels in say 10,000 images are going to be very very large. Now even if you imagine that you write those many rules, it's not very hard to realize that even a supercomputer will take a very long time to compute these many rules and come back with an answer. So it makes obvious sense to understand how the brain of an infant can do this so efficiently (measured in terms of the amount of energy used by the brain and its size).
