Two experiments were conducted with 10 subjects for each to test the hypothesis that two systems underlie the time estimation. One is a timer-system (TS) which processes temporal information, and the other, a cognitive-processing-system (CS) which processes non-temporal information. The method of cross modality ratio matching (between time and visual distance) was used for examinating the effects of modality and memory task on TS and CS outputs. The results showed that an additional memory task during stimulus presentation affected time estimation, and interacted with some other factors such as the duration of stimulus (in Experiment I) and the number of intermittent stimuli (in Experiment II). These results suggested that two processing systems, which are differently affected by memory task, underlie the time estimation. It was not found, however, that modalities of stimulus presentation affected the two systems differently. It seems necessary to study time estimation in relation to other human functions on the basis of an interrelationship between TS and CS.
