The processing of sequences, as opposed to a single interval or duration, also imposes another constraint on the potential mechanisms underlying temporal processing. Let us consider how a spectral model will perform in response to the sequences shown in Figure 10. In a model based on a slow conductance such as an IPSP, the first tone will activate an IPSP of a different duration in each cell. If the second pulse arrives at 50 ms, the 50-ms detector will fire (owing to the interaction between IPSP offset and arrival of the second stimulus). However, the second pulse is also the first pulse of the second interval, and thus to detect the subsequent 150-ms interval, the second pulse would essentially have to reset the inhibitory conductance. We refer to this as the reset problem. When stimulus elements arrive on the same timescale as the intervals being processed, discrimination requires that the event that marks the end of one interval engage the initiation of the timing of the next interval.