**The Kinematic Model**- Hard to treat formally

**Cellular Automata**- Produce a Universal Constructor (UC)

**Excitation-Threshold-Fatigue Model**- Replace the finite automata occupying each cell of the
UC by a suitable neuron

**Continuous Model**- Write partial differential equations for this neuron

**Probabilistic Model**- Introduce probabilities to obtain a stochastic or probabilistic
model

These models represent successive stages in a (projected) research sequence. However, von Neumann stopped working on this topic in 1953, and died in 1957, so the work did not progress beyond Cellular Automata.