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

Abstract

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.