The autonomic-based Concealed Information Test (CIT) relies on differential physiological responses to a specific item. We examined the impact of categorization rules on physiological responses in the CIT. The stimuli were numbers presented in various colors and participants randomly selected one to memorize. The CIT items comprised a number-congruent item, color-congruent item, and incongruent items; none were the same as the memorized item. In Experiment 1, these items were presented under different categorization rules. In the "unworkable" condition, participants were asked about the stimulus they had memorized, whereas in the "workable" condition, they were asked the color of the memorized stimulus. Notably, the number-congruent item in the "unworkable" condition elicited differential responses in electrodermal activity. In the "workable" condition, the color-congruent item prompted differential responses across all electrodermal, cardiovascular, and respiratory measures. No measure indicated a differential response to the number-congruent item. The findings from Experiment 1 were replicated in Experiment 2, where combinations of color and number varied across each repetition under the "workable" condition. This consistent pattern suggests the differential responses in the CIT is rule-based.
