Abstract
This thesis examines the effects of secondary tasks and click trains upon temporal judgement in the context of a Pacemaker-Gate-Counter (PGC) model. All the timing experiments reported employ a paradigm in which subjects are first trained to reliably reproduce a 2.5 s target interval, and are then required to perform time production with a concurrent secondary task. Previous research with digit memory loads has shown that varying memory load had no impact upon concurrent time production (Fortin & Breton, 1995; Fortin & Masse, 1999). Here, it is shown that increasing pitch memory load lengthens time production, but that this is not the case for a colour memory task, or a timbre memory task. The effect obtained with pitch is replicated, and it is demonstrated that the effect is directly due to the processing requirements of retaining pitch information. Furthermore, the pitch effect is not due to a difference in attentional requirements between retaining pitch and retaining digits. Finally, it is shown that the lengthening of time production also occurs when a concurrent duration memory load is increased. In confirmation of previous research (e.g. Fortin, Rousseau, Bourque, & Kirouac 1993), it is shown that when memory-search is performed concurrently with time production, increasing the number of items to be searched causes a lengthening of time production. A novel finding is that the increase in mean time produced is not accompanied by an increase in standard deviation. Furthermore, it is shown that the shortening of mean time production caused by concurrent click trains does not interact with the increase caused by concurrent memory search, and is accompanied by a reduction in standard deviation. These findings are taken to support the separation made in the PGC model between the Pacemaker and Gate components. Overall, the data presented in this thesis provide a number of constraints upon future theorising within the framework of the PGC model and other similar models.