The use of 'artificial saliva' as a neutral control condition in gustatory research
Distilled water with NaHCO3 and KCl, a solution often referred to as artificial saliva because its chemical composition mimics human saliva, is the control liquid of choice in gustatory research, because it is believed to be entirely affectively neutral. Yet evidence that human research volunteers perceive this liquid as emotionally neutral is lacking. Unpublished data from our lab suggested that this solution might be perceived as aversive. This study set out to systematically test the parameters influencing taste neutrality. We used two different concentrations of distilled water with NaHCO3 and KCl, as well as bottled water as a control taste. Healthy adults rated all tastes on two separate scales to rule out an interpretation based on the specifics of a single scale. Our participants rated artificial saliva as aversive on both scales. The bottled water was rated as neutral on both scales, and as significantly less intense in sensation than both concentrations of the distilled water solution. This is the first study to have directly tested the subjective feelings that accompany the ingestion of these oft-used solutions. We found that these liquids, which were previously assumed to be neutral, may not be perceived as such by research participants. Therefore, future gustatory studies should take care when using this solution as a neutral baseline. It is advised that trial-by-trial ratings are collected. Also, depending on the nature of future studies, bottled water may be considered as a preferable neutral baseline.