Are three-sample tasks less sensitive than two-sample tasks? Memory effects in the testing of taste discrimination.

In order to provide insights into why discrimination protocols with three stimuli sometimes tend to be less sensitive than protocols with two stimuli, two experiments were conducted. In these experiments, the relative effects of memory decay and memory interference were investigated. Both experiments involved purified water and/or solutions of low NaCl concentration. In Experiment 1, three protocols were compared: the traditional same-different test (Protocol 1), the same protocol with a rinse between the two samples (Protocol 2), and Protocol 2 with an added time delay between the first sample and the intermediate rinse (Protocol 3.) The decrease in measured d' values as time delay increased indicated that memory decay might be a factor for tests with three stimuli, such as the triangle method, rendering it less sensitive than tests with two stimuli, such as the same-different method. In Experiment 2, four protocols were compared: the traditional same-different test, the two-rinse same-different test, the triangle test, and what will be called duo same-different test. The experimental design allowed the individual consideration of memory decay and interference effects. From this last experiment, the substantial effect of memory interference was uncovered. Further experimentation will be necessary to estimate the exact relative effects of memory interference and memory decay.