In Daniel Kahneman's "Thinking, Fast and Slow", System 1 refers to the rapid unconscious processes that allow instant reactions, for example, if you start to slip, or you reacxh to catch an approaching ball. It is in contrast to System 2, which is slower more reasoned thinking. System 1 is rapid, but may be hard to explain to others. In AI, neural networks and subsymbolic AI in general correspond closely to human System 1 thinking.
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