Neural Networks
Neural networks are computing systems loosely inspired by biological brains. They learn patterns from data by adjusting internal parameters — no explicit programming required. This section covers the biological analogy, how artificial neurons work, and why neural networks are so powerful.
A neuron has:
Information flows from dendrites to axon via the cell body. Axon connects to dendrites via synapses:
In the 1980s, the Pentagon allegedly trained a neural network to detect tanks in photos. They split their photos into training and test sets, and the network learned to identify every test photo correctly.
Then they tested on new photos. The results were completely random.
After investigation, they discovered: all tank photos were taken on sunny days, while tree-only photos were taken on cloudy days. The military was the proud owner of a computer that could tell you if it was sunny.
Note: This story is likely apocryphal, but it’s a perfect illustration of data bias — and why representative, diverse training data matters more than a clever model.