RL 1: Biological foundations and the "Law of Effect" (1898– 1949)
Before GPUs. Before neural networks. Before transistors were even a rumor. There was a hungry cat in a wooden crate, trying to get to a piece of fish. The main character of this era isn't an engineer. It's a loose group of psychologists — some of whom actively disliked each other's ideas — poking at animals to answer one question: why do living things do the things they do? They never wrote a…
1904 — Pavlov's Dogs and the Problem of Prediction
Ivan Pavlov's work on digestion led him to an unexpected discovery about animal behavior. He trained dogs to salivate when presented with food, but noticed they began salivating at the sight of the lab assistant who brought the food or even at the sound of footsteps approaching. This phenomenon became known as Pavlovian conditioning or the conditioned reflex.
Unlike Thorndike's cats, who learned through trial and error, Pavlov's dogs learned through the association of a neutral signal with a consequence. The neutral signal (the metronome, buzzer, light, or tone) became a conditioned stimulus that evoked a conditioned response (salivation) without the presence of the food itself. In reinforcement learning terms, Pavlov's dogs acquired a predictive model of the environment.
The neutral signal served as a cue, predicting the arrival of the food reward. The dogs learned to associate the conditioned stimulus with the unconditioned stimulus (food) and adjusted their behavior accordingly, demonstrating the ability to predict future outcomes based on sensory inputs.
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