Abstract: Three coding systems were designed for a comparative study of the semantic noise which may arise from coding different rates of speed by flash light with different frequencies. It was found that the most effective system is the one in which higher speed was coded by the flash light with higher frequency and lower speed by that with lower frequency. It was suggested that the advantage of this system was due tO its conformity with the subjects habit of thinking which has been established during his daily life.Reaction time and stimulus equivocation Hy(x), which has been taken as a measure of the semantic noise level, have been analyzed, and these two variables were found to be lineally related. The increase of reaction time was explained by the lengthening of decoding processes.

Key words: NULL