The overall goal of this psychophysical method is to determine an individual's most preferred level of sweetness from childhood to adulthood. This method can help answer key questions on taste to determine what factors are related to taste preferences, including dietary intake, age, ethnicity and various measures of health. The main advantage of this technique is that it can be used in young children to directly determine if and how their preferences for taste are different from each other as well as older individuals.

Demonstrating this procedure will be Dr.Nuala Bobowski, a post-doctoral fellow of my laboratory. Begin by obtaining one liter volumetric flasks, one liter amber glass bottles and 100 milliliter amber glass bottles for the preparation, storage and dispensing of five solutions. For testing, obtain the following materials:30 milliliter disposable medicine cups for solutions, drinking cups containing water for rinsing in between trials, a stopwatch to monitor inter-pair and inter-series intervals, distilled water for solution preparation and rinsing, and a cup for expectoration if a sink is not available.

Then obtain a sheet of paper labeled with the numbers one and two, representing the order of tasting, and a tracking grid for recording data. Next, clean and sterilize all bottles in an autoclave. Label each bottle with the date and stimulus label A, B, C, D and E.According to this table, weigh the appropriate amount of sucrose to make solutions A through E.Make one solution at a time by placing the appropriate grams of sucrose in a one liter volumetric flask and fill to the line on the flask with distilled water.

Mix to dissolve the sucrose. Then, once the sucrose is dissolved, transfer the solution to the appropriately labeled one liter amber glass bottle. Store each bottle with solution in the refrigerator at four degrees Celsius for a maximum of one week.

Finally, construct a tracking grid to record subject data. Label each grid with a series number, either one or two, and the concentrations of the sucrose solutions. Include space to record the start and end times of each series as well as a column on each grid to record notes during the test.

Prior to the testing day, instruct the subject to not eat or drink for at least one hour before testing. Two hours before testing, remove the solutions from the refrigerator, and transfer approximately 100 milliliters of each to the appropriately labeled 100 milliliter amber glass bottles. Then allow the solutions to equilibrate to room temperature.

Next, seat the subject at a table in front of the sheet or paper labeled with the numbers one and two, and allow him or her to acclimate to the testing room and the tester for at least 10 minutes. Inform the subject that he or she is going to play a game with things to taste from two different cups. Inform the subject that he or she will have to taste what is inside the first cup, swish it around in his or her mouth without swallowing and spit out the solution when told to do so in the sink or cup.

Then tell the subject that he or she will rinse his or her mouth with water, taste what is in the second cup in the same manner and ultimately point to which cup he or she liked better. Tell the subject that there are no right or wrong answers and that we simply want to know which of the pair tastes better. For series one, begin by placing two cups respectively containing five milliliters of solution B and five milliliters of solution D on a sheet of paper labeled with the numbers one and two in front of the subject.

Place solution B directly on number one and present it to be tasted first. Then place solution D directly on number two and have the subject taste it second. Using the tracking grid, underline the concentration that is presented first, which is solution B.Next, instruct the subject to taste the solution in position one by swishing.

After five seconds, instruct the subject to expectorate, rinse his or her mouth out with water and to expectorate again. Then instruct the subject to taste the solution in position two by swishing and to expectorate after five seconds. Ask the subject to point to the solution that he or she liked better.

Circle the X on the tracking grid that corresponds to the subject's preferred concentration. Next, have the subject rinse his or her mouth twice with water and expectorate. Wait one minute before presenting the next pair of solutions.

For the second comparison of solutions in series one, pair the preferred concentration from comparison one with the next-lowest concentration. For example, if the subject preferred solution D in the first pair, present the second pair consisting of solution D and the next-lowest concentration, solution C.Place solution C in position one and solution D in position two. Indicate which solutions are being presented by marking Xs on the grid and underline the X that corresponds to the solution presented in position one.

Repeat this process until the subject chooses the same concentration twice consecutively when presented with both a lower and higher adjacent concentration or when the subject chooses either the lowest or highest concentration twice consecutively. Record each subject's preferred concentration from series one on the grid and wait three minutes before beginning series two. For series two, pour five milliliters of each of solutions B and D into disposable cups.

Place solution D on number one and solution B on number two in front of the subject. Underline the concentration that is presented first on the grid, which is solution D.Instruct the subject to taste and expectorate the solutions in the same manner as done for series one. For the second comparison of solutions in series two, pair the preferred concentration from the first comparison with the next-highest concentration.

For example, if the subject prefers solution D in the first pair, present the second pair consisting of solution D and the next-highest concentration, solution E.Place solution E in position one. Finally, record the subject's preferred concentration from series two by circling it on the grid. The determination of the participant's preferred level of sucrose was estimated by calculating the geometric mean of the final concentration chosen in each series.

Here the geometric means from both series one and two are shown for data collected from 930 children, adolescents and adults. This figure illustrates that the most-preferred level of sucrose is significantly higher for children and adolescents than it is for adults. After watching this video, you should have a good understanding of how to conduct the Monell two-series forced-choice pair-comparison tracking method for determining sweet taste preferences throughout the lifespan.

Thanks for watching, and good luck with your experiments.