Difference test sensitivity: Comparison of three versions of the duo-trio method requiring different memory schemes and taste sequences

The duo-trio test is a simple non-directional difference test method suitable for discriminating subtle differences between confusable stimuli. It is suitable for consumers as well as trained panelists. In the present study, the influence of memory and tasting sequence in the duo-trio was investigated, using various low concentrations of NaCl in a roving discrimination design. Three versions of duo-trio protocols were considered. The first protocol was the traditional duo-trio with the reference tasted first (DTF). The second protocol was the duo-trio with the reference tasted in the middle, between the two test samples (DTM). The third protocol was the duo-trio with the reference tasted twice, first and last as a reminder (DTFR). In some conditions, the higher concentration of NaCl solution was the reference (W-odd); in others, the lower concentration was the reference stimulus (S-odd). Calculated d′ values indicated a superior performance for the DTFR over the DTF and DTM. In the DTF, S-odd yielded a lower d′ than W-odd, probably due to NaCl taste adaptation. In the DTFR, the effects of adaptation were counterbalanced for all the stimuli including the reference, resulting in no significant sequence effect. In the DTM, the sequence of the first two stimuli in the test had a significant effect on the performance, probably due to the decision strategy used for the protocol. Manipulation of the reference in the duo-trio test introduces issues such as attention as well as memory and adaptation.