The data consisting of some indices of short-term memory, of school results, and of retrospective estimates of stimulation unintentionally perceived either while performing a mental task (memorization and comparison of stimuli) or without it - was collected on IX-X form schoolchildren. It has been shown that perception of stimulation in presence of a mnemic load results in more adequate retrospective estimation of its temporal, quantitative and qualitative parameters. More than that, only under conditions of mnemic load there is a significant correlation between indices of retrospective estimation of time, as well as correlation between stimulation estimates and the capacity of children's short-term memory and their school results.