The main objective of the present study was to determine whether event-related potentials (ERPs) predominant in prefrontal cortex (PFC) respond in a similar fashion to ERPs predominant in posterior parietal cortex (PPC) in duration and size discrimination tasks. The results indicate that contingent negative variation (CNV) and P300 components changed according to task demands. In the time-related task, amplitudes and duration of both components increased as a function of stimulus duration and easier discriminability. This was not the case in the size discrimination task. These results are in accordance with the hypothesis of a functional link between PFC and PPC in timing behavior. The later-appearing LPCt component was observed in both tasks, but its amplitude increased only as a function of stimulus duration.