Abstract: The tactile sensitivity of forearm to summate the length of plexiglass rectangles was tested. A single rectangle and a complex formed from 2 to 5 rectangles were used as the variable stimuli, which were compared with the single standard stimulus. The main result of the experiment was that there was no significant difference in the mean thresholds between discriminations of lengths in the experiments using single and complex variable stimuli. This result is consistent with the experiment using complex standard stimuli. It has been suggested that the subjective measurement with a mental ruler seems to be a general scheme of performance of subjects in tactile length perception and that the length summation requires more intensive and effective use of strategy than discrimination of single length.

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