Psychophysical Tracking Method to Assess Taste Detection Thresholds in Children, Adolescents, and Adults: The Taste Detection Threshold (TDT) Test

This protocol describes a method that measures the sensitivity of the taste system. This is an important dimension of taste that is independent of taste hedonics. The TDT test can be used in old and young.

It's very easy to understand. It requires less than 15 minutes to complete and uses a very strict set of criteria ensuring a stable outcome measure. Participants should be comfortable and well-informed, and if they don't know which of the pair tests different from water, they just can guess.

There are not really right or wrong answers. To make a tastant stock solution, in this case, the stock solution for sucrose, weigh 684.6 grams of sucrose in a disposable weigh boat using a balance that is accurate to 0.01 grams. Then transfer the weighted tastant to a two-liter beaker.

Add water to the beaker to dissolve the sample and rinse the weigh boat with distilled water. Then, pour this distilled water wash into the two-liter beaker. Use a funnel to transfer the tastant solution to a two-liter volumetric flask.

Then rinse the beaker and funnel with more water, pooling the wash in the flask. Fill the flask with water to the two-liter mark. Place a stopper onto the flask and invert to mix until the tastant is completely dissolved.

To prepare the intermediate tastant solutions add 560, 320, 180 and 100 milliliters of the tastant stock solution to each of four flasks labeled one to four, respectively. Then fill each flask to a final volume of one liter with distilled water. Close the flasks with their stoppers and mix by inversion.

Pour the contents of each flask into an appropriately labeled one-liter glass bottle and pour any remaining tastant stock solution into a glass bottle labeled with the tastant name. Store all bottles at four degrees Celsius. To prepare the remaining working tastant solutions, arrange 12 bottles labeled five to 16 in a four-by-four grid with the intermediate tastant solution bottles one to four placed in the front row.

Always starting with the most dilute solution in a row, transfer 50 milliliters of the tastant solution from bottles four to one into bottles eight to five, respectively. Then add 450 milliliters of distilled water to each bottle from five to eight. After inverting the bottles to mix, repeat the dilution between bottles eight to five and 12 to nine, and then bottles 12 to nine and 16 to 13 until all 16 working tastant solutions have been prepared.

Remove bottles containing the tastant solutions and distilled water from the refrigerator and transfer about 120 milliliters of solution for each step into appropriately labeled sterilized glass bottles two hours before testing. Before performing a taste detection threshold test, determine the random order sequence of the tastant and record it in the tracking grid. If water is presented in position one, enter W.And if the tastant is presented in position one, enter T.Before performing a taste detection threshold test, show the medicine cups to the participant and say-We're going to play a game with things to taste.

Here, you see two cups:Number one and number two. I will first give you enough to taste for this in cup number one. Swish it around your mouth, but don't swallow.

I tell you when to spit it out, okay? Mm-hmm.You will then rinse with water and taste what's in cup number two. I will tell you when to spit it out.

Then I want you to point to the cup which has the taste. If you're not sure, just guess.Okay. You will then rinse your mouth with water two times and we're gonna do this again.

There are no right or wrong answers. All we wanna know is which one you think has a taste.Okay. To perform a taste detection threshold test, add approximately 10 milliliters of the appropriate starting concentration of tastant to one medicine cup, and about 10 milliliters of distilled water to the second medicine cup, and place both cups in positions one and two in front of the participant.

Instruct the participant to taste the solution in position one by swishing. After five seconds, instruct the participant to expectorate, and then rinse their mouth with water without swallowing. Next, instruct the participant to taste and expectorate the solution in position two in the same manner.

After rinsing, ask the participant to point to the solution that has a taste or that tastes different than water. After every response, thank the participant for doing a good job, and have the participant rinse their mouth again. Place a plus sign on the grid if the participant picked the cup with the tastant to indicate a correct response, and write a minus sign if they picked the cup with water to indicate an incorrect response.

For the second pair of tastant, if the participant was incorrect for the first pair, proceed up on the grid, noting that the tastant in the second pair will be the next higher concentration. If the participant was correct, the tastant in the second pair will be the same step tastant. Refer to the grid for the order of tastant presentation.

Place the appropriate tastant in front of the participant as indicated by the grid, and have the participant repeat the taste test as just demonstrated. Continue the tasting process moving up the grid to the next higher concentration with each incorrect answer or down the grid to the next lower concentration after two correct answers in a row. Circle any steps on the grid for which a change in direction in the accuracy of the participant's response is observed, referred to as a reversal.

Continue with the taste testing until four reversals are achieved or until the participant reaches the end of the grid in either direction and list the step numbers of these four reversals. To determine the participant's detection threshold use this formula to calculate the arithmetic mean of the log values of the molarity of the four reversals. In this representative taste analysis, the participant's responses met the criteria within the first four reversals, because there were no more than two steps between any two successive reversals, and there were two sets of pairs in which the participant correctly identified the tastant twice at the same step.

In this taste test, the participant demonstrated a relatively high sucrose detection threshold, but the responses for the first four reversals did not meet the criteria, because there were no two sets of pairs in which the participant correctly identified the tastant twice at the same step. The next set of reversals did meet the criteria, because there were no more than two steps between any two successive reversals, and two sets of two correct answers in a row were obtained at the same step. For this participant with a relatively low sucrose detection threshold, the first four reversals also did not meet the criteria, although in two pairs, the participant correctly identified the tastant twice at the same step.

There were more than two steps between reversals three and four. The last four reversals in this analysis met the criteria, because there were no more than two steps between any two successive reversals, and the participant correctly identified the same concentration for two pairs. This same method is used to calculate thresholds for other taste modalities such as salty and MSG.

It is of utmost importance that the tastants and distilled water that will be tasted or used during testing are at the same temperature before initiating the test. Otherwise, participant may choose a solution based on temperature. Thresholds for more than one basic taste can be measured on the same testing day in adults, but because children have shorter attention spans, determining more than one threshold per day could be problematic.