Attention has been widely reported to alter estimates of time in the range of seconds (Hicks et al., 1976; Macar et al., 1994; Brown, 1997; Coull et al., 2004). Internal clock models can account for attention- dependent effects in the second range by assuming a gating mechanism that controls the number of events generated by the oscillator that are counted by the accumulator (Meck, 1984; Zakay and Tsal, 1989). In contrast, on the shorter time scale, divided attention or cognitive load does not appear to specifically alter temporal judgments (Rammsayer and Lima, 1991; Lewis and Miall, 2003). Therefore, the SDN model would be expected to be fairly insensitive to shifts in attention.However, recent studies have revealed that temporal distortions of short intervals can be produced by saccades or stimulus features (Morrone et al., 2005; Johnston et al., 2006). These studies suggest that on short scales, timing is local, and are generally consistent with the SDN model that predicts that temporal processing could occur in a number of different cortical areas on an as-needed basis.

An explanation often used for changes in discriminative sensitivity is that of ``attention’’ , in the specific sense of exposing animals to situations that force them to ``attend to’ ’ (or have their behaviour brought under the control of) a particular stimulus dimension and ignore irrelevant competing dimensions.

However, the word ``attention’’ has another sense in everyday usage, which is perhaps more pertinent here- -the idea of differential allocation of processing resources in different conditions; thus when we pay particular attention’’ , we allocate some sort of psychological resource so that the processing of an event is particularly precise, careful, and error-free (e.g. Kahneman, 1973). So, for example, in the timing tasks discussed above, difficult conditions cause subjects to process durations more carefully than they do in ``easy’ ’ conditions, so time discrimination becomes more sensitive.