Representative examples of temporal relationships between the conditional stimulus (CS) and the unconditional stimulus (US). A. Short-delay conditioning to a continuous tone CS. The CS duration is 15.6 s, the interstimulus interval (ISI) is 14.6 s, and the US duration is 1 s. Note that the CS and US overlap temporally. B. Short-delay conditioning to a discontinuous tone (termed "Pips"). The only difference from A is that the CS is discontinuous. C. Long-delay conditioning to a continuous tone. The CS duration is 27 s, the ISI is 26 s, and the US duration is 1 s. Again, the CS and US overlap temporally. D. Trace conditioning to a continuous tone. The CS duration is 10 s, the ISI is 26 s, and the US duration is 1 s. The CS and US do not overlap temporally. Instead, a 16 s "trace interval" separates the CS offset from the US onset. Note that the ISI is the same in parts C and D. Modified from Bang and Brown (2009b).