Optimal difference test sequence and power for discriminating soups of varying sodium content: DTFM version of dual-reference duo-trio with unspecified tetrad tests.

As sodium reduction has become very important in the food industry, various types of unspecified duo-trio tests have been studied to improve its efficiency for studying samples with high sodium content, and a constant-saltier-reference duo-trio test with dual reference, one reference in the first position and the second reference in the middle between the two test stimuli (DTFM), has been recommended. For the duo-trio test, a 'comparison of distance' (COD) strategy has been generally assumed. Yet, theoretically for DTFM, the 2-AFC reminder (2-AFCR) τ-strategy is also possible, which would make DTFM more efficient than the unspecified tetrad test. In this study, the hypothesis was that when subjects are pre-exposed to two types of samples, the 2-AFCR τ-strategy can be adopted in a constant-reference DTFM using a fixed design experiment. In order to test this hypothesis, unspecified tetrad tests involving categorization tasks were used as a means of pre-exposure to the two types of samples for DTFM, and a performance comparison was conducted. Two groups of 39 untrained/naive subjects performed both the unspecified tetrad and DTFM tests in varying orders for the purpose of discriminating two different soup samples of varying sodium content. A comparison of the d' estimate across different methods supported the hypothesis that the more efficient 2-AFCR τ-strategy was appropriate when the tetrad test preceded DTFM, while when DTFM was performed first without pre-categorization of samples, the conventional duo-trio COD strategy was appropriate for the constant-reference DTFM.