The utility of artificial neural network models lies in the fact that they can be used to infer a function from observations. This is particularly useful in applications where the complexity of the data or task makes the design of such a function by hand impractical.
The tasks artificial neural networks are applied to tend to fall within the following broad categories:
- Function approximation, or regression analysis, including time series prediction, fitness approximation and modeling.
- Classification, including pattern and sequence recognition, novelty detection and sequential decision making.
- Data processing, including filtering, clustering, blind source separation and compression.
- Robotics, including directing manipulators, Computer numerical control.
Application areas include system identification and control (vehicle control, process control, natural resources management), quantum chemistry, game-playing and decision making (backgammon, chess, poker), pattern recognition (radar systems, face identification, object recognition and more), sequence recognition (gesture, speech, handwritten text recognition), medical diagnosis, financial applications (automated trading systems), data mining (or knowledge discovery in databases, "KDD"), visualization and e-mail spam filtering.
Artificial neural networks have also been used to diagnose several cancers. An ANN based hybrid lung cancer detection system named HLND improves the accuracy of diagnosis and the speed of lung cancer radiology. These networks have also been used to diagnose prostate cancer. The diagnoses can be used to make specific models taken from a large group of patients compared to information of one given patient. The models do not depend on assumptions about correlations of different variables. Colorectal cancer has also been predicted using the neural networks. Neural networks could predict the outcome for a patient with colorectal cancer with a lot more accuracy than the current clinical methods. After training, the networks could predict multiple patient outcomes from unrelated institutions.
Neural networks and neuroscience
Theoretical and computational neuroscience is the field concerned with the theoretical analysis and computational modeling of biological neural systems. Since neural systems are intimately related to cognitive processes and behavior, the field is closely related to cognitive and behavioral modeling.
The aim of the field is to create models of biological neural systems in order to understand how biological systems work. To gain this understanding, neuroscientists strive to make a link between observed biological processes (data), biologically plausible mechanisms for neural processing and learning (biological neural network models) and theory (statistical learning theory and information theory).
Neural networks are being used:
in investment analysis:
to attempt to predict the movement of stocks currencies etc., from previous data. There, they are replacing earlier simpler linear models.
in signature analysis:
as a mechanism for comparing signatures made (e.g. in a bank) with those stored. This is one of the first large-scale applications of neural networks in the USA, and is also one of the first to use a neural network chip.
in process control:
there are clearly applications to be made here: most processes cannot be determined as computable algorithms. Newcastle University Chemical Engineering Department is working with industrial partners (such as Zeneca and BP) in this area.
networks have been used to monitor
the state of aircraft engines. By monitoring vibration levels and sound, early warning of engine problems can be given.
British Rail have also been testing a similar application monitoring diesel engines.
networks have been used to improve marketing mailshots. One technique is to run a test mailshot, and look at the pattern of returns from this. The idea is to find a predictive mapping from the data known about the clients to how they have responded. This mapping is then used to direct further mailshots.
Successes and Failures
It's fine in theory to talk about neural nets that tell males from females, but if that was all they were useful for, they would be a sad project indeed. In fact, neural nets have been enjoying growing success in a number of fields, and significantly: their successes tend to be in fields that posed large difficulties for symbolic AI. Neural networks are, by design, pattern processors - they can identify trends and important features, even in relatively complex information. What's more, they can work with less-than-perfect information, such as blurry or static-filled pictures, which has been an insurmountable difficulty for symbolic AI systems. Discerning patterns allows neural nets to read handwriting, detect potential sites for new mining and oil extraction, predict the stock market, and even learn to drive.
Interestingly, neural nets seem to be good at the same things we are, and struggle with the same things we struggle with. Symbolic AI is very good at producing machines that play grandmaster-level chess, that deduce logic theorems, and that compute complex mathematical functions. But Symbolic AI has enormous difficulty with things like processing a visual scene (discussed in a later chapter), dealing with noisy or imperfect data, and adapting to change. Neural nets are almost the exact reverse - their strength lies in the complex, fault-tolerant, parallel processing involved in vision, and their weaknesses are in formal reasoning and rule-following. Although humans are capable of both forms of intellectual functioning, it is generally thought that humans possess exceptional pattern recognition ability. In contrast, the limited capacity of human information processing systems often makes us less-than-perfect in tasks requiring abstract reasoning and logic.
Critics charge that a neural net's inability to learn something like logic, which has distinct and unbreakable rules, proves that neural nets cannot be an explanation of how the mind works. Neural net advocates have countered that a large part of the problem is that abstract rule-following ability requires many more nodes than current artificial neural nets implement. Some attempts are now being made at producing larger networks, but the computational load increases dramatically as nodes are added, making larger networks very difficult. Another set of critics charge that neural nets are too simplistic to be considered accurate models of human brain function. While artificial neural networks do contain some neuron-like attributes (connection strengths, inhibition/excitation, etc.) they overlook many other factors which may be significant to the brain's functioning. The nervous system uses many different neurotransmitters, for instance, and artificial neural nets do not account for those differences. Different neurons have different conduction velocities, different energy supplies, even different spatial locations, which may be significant. Moreover, brains do not start as a jumbled, randomised set of connection strengths, there is a great deal of organization present even during fetal development. Any or all of these can be seen as absolutely essential to the functioning of the brain, and without their inclusion in the artificial neural network models, it is possible that the models end up oversimplified.
One of the fundamental objections that has been raised towards back-propogation style networks like the ones discussed here is that humans seem to learn even in the absence of an explicit 'teacher' which corrects our outputs and models the response. For neural networks to succeed as a model of cognition, it is imperative that they produce a more biologically (or psychologically) plausible simulation of learning. In fact, research is being conducted with a new type of neural net, known as an 'Unsupervised Neural Net', which appears to successfully learn in the absence of an external teacher.
One drawback to using artificial neural networks, particularly in robotics, is that they require a large diversity of training for real-world operation. A. K. Dewdney, a former Scientific American columnist, wrote in 1997, "Although neural nets do solve a few toy problems, their powers of computation are so limited that I am surprised anyone takes them seriously as a general problem-solving tool." (Dewdney, p. 82)
Arguments for Dewdney's position are that to implement large and effective software neural networks, much processing and storage resources need to be committed. While the brain has hardware tailored to the task of processing signals through a graph of neurons, simulating even a most simplified form on Von Neumann technology may compel a NN designer to fill many millions of database rows for its connections - which can lead to excessive RAM and HD necessities. Furthermore, the designer of NN systems will often need to simulate the transmission of signals through many of these connections and their associated neurons - which must often be matched with incredible amounts of CPU processing power and time. While neural networks often yield effective programs, they too often do so at the cost of time and monetary efficiency.
Arguments against Dewdney's position are that neural nets have been successfully used to solve many complex and diverse tasks, ranging from autonomously flying aircraft to detecting credit card fraud. Technology writer Roger Bridgman commented on Dewdney's statements about neural nets:
Neural networks, for instance, are in the dock not only because they have been hyped to high heaven, (what hasn't?) but also because you could create a successful net without understanding how it worked: the bunch of numbers that captures its behaviour would in all probability be "an opaque, unreadable table...valueless as a scientific resource". In spite of his emphatic declaration that science is not technology, Dewdney seems here to pillory neural nets as bad science when most of those devising them are just trying to be good engineers. An unreadable table that a useful machine could read would still be well worth having.
Some other criticisms came from believers of hybrid models (combining neural networks and symbolic approaches). They advocate the intermix of these two approaches and believe that hybrid models can better capture the mechanisms of the human mind (Sun and Bookman 1994).