A third noteworthy feature of SA patterning, seen in Fig. 1, is that on both R and N trials responding progressively increased over the 90-s intertrial interval. If SR and SN were fading stimulus traces, as some suggest, an opposite pattern of responding should have been obtained, i.e., a progressive decline in responding over the 90-s interval. Also to be noted is that a trace view suggests that discrimination between R and N trials should have decreased over the 90-s interval, and, as Fig. 1 shows, it did not. When the CS was presented, SA patterning was maintained and responding increased both on R and N trials, indicating that the CS was excitatory.