Table 1.

Methods used to assess detection and recognition thresholds and intensity perception.

	Psychophysical Task	Stimulus Presentation	Stimulus
Detection and recognition threshold	Constant stimuli: In which taste stimuli are presented randomly and performance is assessed allowing for the derivation of a psychometric function. A “hit” is defined as when the participant correctly reported that the stimulus was different from water when stimulus was presented. A “false alarm” is defined as when the participant incorrectly reported that the stimulus was different from water when water was presented [50]. 2-Alternative Forced Choice (2-AFC): Participants are asked to differentiate the tastant from water, in multiple trials. The test begins at a concentration at which the tastant can be detected/recognised. After two correct trials, the test moves to a lower concentration, while a single incorrect trial leads to a higher concentration. The threshold is calculated based on the reversal concentrations. This type of test is sometimes referred to as a staircase [61]. 3-Alternative Forced Choice (3-AFC): Two samples of water and a sample of tastant are tasted at separate times for each trial. The detection threshold is the lowest concentration to receive two successive correct responses by the subjects just above the immediate lower concentration at which two successive incorrect responses are given or simply as the lowest concentration, the difference between the three drops can be detected. The recognition threshold refers to the concentration at which the subject can identify the taste quality [62]. Burghart taste strip test: The technique is based on strips made from filter paper which were impregnated with different taste solutions (four concentrations each for sweet, sour, salty and bitter). These strips are placed on the tongue and subjects are asked to identify the taste quality [63].	Method of limits: Target tastants are offered in increasing (ascending) or decreasing (descending) concentrations. The threshold refers to the minimum concentration for taste detection. Method of constant stimuli: Stimuli of variable concentrations are presented in a random order to participants. Concentrations range from those which are known to be subthreshold and supra-threshold. The threshold is the concentration of the stimulus, perceived in more than half of the presentations. Adaptive method: The initial stimulus is a known supra-threshold stimulus, and is followed by stimuli of concentrations that decrease in predefined steps. The series is stopped when the stimulus strength becomes subthreshold. Then, the step is halved and increasing concentrations are given until the subject perceives the taste again. This process is repeated several times, reversing each time, until the step size reaches the preset minimal value. With this method, the threshold value can be delineated very accurately.	Solutions Model foods/beverages Filter papers
Intensity	Category scales: These are numeric scales and generally comprise descriptors equally spaced across a line (e.g., ranging from “1 = no taste” to “9 = extreme taste”). Common examples are the 9-point scale or visual analogue scale (VAS). General labelled magnitude scale (gLMS): This comprises a top anchor (‘strongest imaginable sensation of any kind’), an opposite anchor (‘barely detectable’) and intermediate labels.	Random order: stimuli are presented in a random order of intensity. Increasing concentrations: stimuli are presented in an order of increasing intensity	Solutions Model foods/beverages Filter papers