4. It is a well-known physiological phenomenon that if a cold stimulus is applied to a person’s skin for a very short period of time, the person will perceive heat. However, if the same stimulus is applied for a longer period, the person will perceive cold. The use of discrete time steps enables the McCulloch-Pitts network drawn below to model this phenomenon. Neurons x1 and x2 represent receptors for heat and cold, respectively, and neurons y1 and y2 are the counterpart perceptors. Neurons z1, z2 are auxiliary neurons. As shown, each neuron has a threshold of 2. Input to the system will be (1, 0)

if heat is applied and (0, 1) if cold is applied. Verify that this network correctly models this phenomenon—in other words, if a cold stimulus is applied for only one time step, heat will be perceived. However, if the cold is applied for two time steps, then cold will indeed be perceived. Notice, we allow this network to possess weights.