Abstract: Field experiments, in which locomotive enginemen and college students served as subjects, were conducted for further study on the semantic noise in coding flash signals. The results confirmed our previous findings that the best coding system is the one in which higher rate of speed was coded by flashes of higher frequency, and lower speed by that of lower frequency, and that the reaction time and the semantic noise level were linearly related.The results also indicated that in different coding systems there exist different logical orders which have some relationship with the subject's habit of thinking, and these are important factors that influence the semantic noise level. Contrary to our expectations, no significant difference has been found between the habit of thinking of the enginemen and that of the college students. It seems probable that daily life experience is a more dominant factor than professional experience in the formation of habit of thinking relevant to our experimental conditions.

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