Thursday, 29 May 2014

Brains are More than Threshold Units

I was reading the following article yesterday:

Laser mimics biological neurons using light

The article is about a component that can emit a laser depending on the intensity of light hitting it. In technical language, this is called a threshold unit. In fact, a threshold unit is a concept. It is a name used to describe any kind of material/device/stuff which can receive some kind of input, be it in the form of energy, information or anything else, and emit something else whenever the input amount exceeds some threshold value.

The connection of threshold units with the brain is that neurons are a kind of threshold unit. There are many different kinds of neurons. Some of them are constantly emitting pulses of electricity at a certain frequency, while others remain "silent" until they become excited. An "excited" neuron changes its firing frequency whenever the amount of electricity it receives from other neurons to which it is connected goes above some value. As you can easily notice, this value is the threshold in a threshold unit.

The simplest threshold unit is the famous perceptron. The perceptron is not an object, it is a mathematical model that was developed to mimic the main function of the neuron. The perceptron is a mathematical structure with a certain number of "boxes" that work as input entries and one output box that spills out a number whenever the inputs get larger than some value. These models date back to the 1950's.

Because the perceptron is a mathematical model, one can fit any threshold unit to something similar to a perceptron. During decades, perceptrons and other kinds of neural networks created by connecting perceptrons in many different ways have been studied. They are capable of memorization and learning under certain limits.

Then, might ask, why am I being picky and saying that the brain is more than threshold units? Neurons are threshold units and threshold units can be used to construct neural networks, but what makes a network learn is the pattern of connections of its units, not the units themselves. The point is that knowledge is not stored in the units, it's stored in the links they form with each other. If you put trillions of threshold units in a regular square network, nothing will ever happens in terms of learning. Without learning, thinking is not that great... So, what is missing?

The answer receives the name of plasticity. This is the capacity that neurons possess of creating new connections and cutting old ones. This is what changes the patterns and makes memorization and generalization (the two pillars of learning) possible. Although faster threshold units like the ones in the article might improve the speed of information transmission, that is not a guarantee that it will improve higher abilities like creativity and understanding. It might lead to faster reflexes, for instance, but not faster learning as it has nothing to do with creating and severing connections.

It is not that the article does not describe an interesting work. It is, but one needs to be very careful with the actual implications of each line of research when we read about a new 'big breakthrough' every week...


Friday, 23 May 2014

Nobody Likes Serious Research, People Like Easy Rules

I read this article on The Guardian these days:

A big, juicy burger to anyone who knows what healthy eating is any more

The article is about how there are many contradictory recommendations about what constitutes a healthy diet. The article is not very good and does not have many useful information. It is another of those thousands of articles trying to sound smart and sarcastic and achieving very little. Too bad too many people love this kind of article.

Anyway, what bothered me more was one of the comments of some readers saying that more 'serious research' on the subject was needed. Let me state something concerning this: the general public don't like serious research. The one thing that people want is someone to tell them rules like 'you have to eat six tomatoes per day' or 'never eat sugar'.

Serious research will not give you those rules because they simply do not exist. It is not difficult to understand that the amount of nutrients one should or should not eat depends heavily on a huge number of variables. It depends on genetics, health conditions, on how much exercise you do and even on the weather features of the place you live. All of that can affect the way your body metabolizes food and how much of each nutrient is needed.

All those articles that you see in the news about correlations between a certain amount of food and healthy problems are interesting, but their limitations should be considered. Usually they only represent correlations, not cause and effect. They are also difficult to analyse because many variables, which are themselves hard to control, might be affecting the results. Also, samples are usually small, which does not help in the statistical analysis, especially when they rely on wrong techniques.

The reason we have lots of this kind of articles with great repercussion is because that's exactly what people want. If there is one thing that I've learned in my academic career is that people do not want to support serious research, they want to support research that have a 'clear conclusion', that is fast and that will give them a rule they can follow and then blame others if it doesn't work. That is, surely, not serious research.

That's, unfortunately, how most research today works. It's not the scientist's fault. A scientist has to survive and has to do whatever there is money to do. We live in a world in which people don't mind lending their money for free to bankers and at the same time think that scientists are robbing society's money when they try to understand something deeply.

If you really want to understand what constitutes 'healthy eating' you should be prepared to support research that will probably take decades and will not result in a recipe book. For most things in life there are no simple rules.

Stating the Obvious Again

Good to find that I am not the only one to see that. By the way, before you smile and nod your head agreeing with the words, take a moment to reflect if that is not the way you actually see education.