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Fig. 2.9. Solving the superposition catastrophe through temporal coding. If firing rates of neurons alone are used to represent objects, multiple objects in the scene can result in confusion. (a) A square and a triangle are presented in the retina. In the cortex plot, the neurons responding to the square are colored gray, and those responding to the triangle white. When both populations of neurons are active at once, it is impossible to know which neuron is representing which object. This problem is known as the superposition catastrophe (von der Malsburg 1981, 1986a, b). One solution is temporal coding, where temporal information is used to separate the two populations. Neurons representing one object activate at one time step, and neurons representing the other object activate at the next time step, as shown in (b).