The existence of an internal clock and its involvement in information processing has been investigated in humans using the experimental protocol of Treisman et al. (1990) [Treisman et al., 1990. Perception, 19, 705 – 743]. In this protocol, a periodical stimulation, which is assumed to drive an internal clock, is delivered during a reaction time (RT) task. The accelerating or slowing down effects of the periodical stimulation, according to its frequency, allowed an estimate to be made of a simple harmonic of the frequency of the internal clock. The estimate was close to 21 Hz. In the framework of the serial model of information processing, the present work investigates the involvement of the internal clock in the transmission of information between processing stages during RT. The data tend to support the idea that the internal clock allows the transfer of information from one stage to the next one at definite moments only, periodically distributed in time. According to our results, and recent data from the literature on electric cortical oscillations, we propose a model of an internal clock sending periodic inhibition, which would permit an increased signal/noise ratio in the processing and the transmission of information in the central nervous system.