Assessment of Spatial Lingual Tactile Sensitivity using a Gratings Orientation Test

This video illustrates a procedure to assess spatial lingual tactile size sensitivity using a grating orientation test. Similar tools have been used to measure tactile acuity at the body level, and particularly on the fingertips of the hands. However, few methodological approaches exist to measure sensitivity at the oral level.

And specifically on the tongue. This procedure can be helpful in the medical feed to study the association between oral tactile sensitivity, speech clarity, and swallowing disorders, as well as in sensory consumer studies to explore individual variation in texture perception, food preferences, and eating behavior. Demonstrating the procedure will be Camilla Cattaneo post doc fellow, Marta Appiani research assistant student and Noemi Sofia Rabitti, PhD student at the university of Milan.

Prior to the test, the experimenter must be trained to standardize the force applied on the subjects tongue. Take the tool and apply a force of 100 grams on a sponge placed on a scale. Display all gratings on a table.

Once the participant sits on a comfortable chair, inform the participant that they can leave the experiment at any time. Inform the participant that they will be blindfolded during the experiment and asked to stick out their tongue in a comfortable and relaxed way. To familiarize the subjects with the procedure.

Use the largest grating of 1.25 millimeter to demonstrate the force applied. Notify the participants that they can take a sip of water whenever deemed appropriate. Apply each grating onto the subject's tongues at the anterior region around the midline.

After each touch ask the subjects to indicate the tools vertical or horizontal orientation and their degree of sureness. Subjects must guess if they do not know. After each touch, record all the answers for each subject on a spreadsheet and repeat each grating as many times as deemed necessary.

Prepare a solution consisting of 20 milliliters of sodium hypochlorite diluted in one liter of water according to the manufacturer's instructions. Manually shake the solution for a few seconds, fill six cups with approximately 20 milliliters of the disinfectant solution to fully immerse each tool in the solution. Place each tool in the corresponding cup and let the tools soak for 15 to 20 minutes.

Rinse the tools with plenty of water and allow the tools to air dry. Create a response matrix for each volunteer and all the tools based on the response frequencies used to calculate the R-index using the R-index equation. This is an example of a data set, for each subject the R-index values in bold are the ones used to calculate the subjects threshold by interpolating the two R indices immediately below and above the cutoff.

In the current study, each grating was repeated six times and the corresponding tabulated cutoff was 0.74. The performance for the six gratings and the derived R-index threshold estimate of one subject is reported in the current study. In this case, the threshold corresponds to 0.99 millimeters.

The subjects with low threshold values were able to recognize a smaller bar size and were sensitive. In comparison, the subjects with high threshold values required more input with a larger bar size to perceive the stimulus cognitively and were less sensitive. In the shown case threshold values ranged from 0.20 to 1.2 millimeters.

The subjects with a threshold less than 0.20 millimeters, were able to recognize the orientation of the squares from the smallest size. Conversely, the subjects with a threshold value greater than 1.25 millimeters could not discriminate any of the grating sizes. An example of a threshold data set is represented.

It is very important that the experimenters are treated and calibrated before conducting the test to ensure that a concept and standardized force is exerted on the subjects tongues. This protocol shows a new innovative way to measure lingual tactile acuity and allows us to study the association between oral tactile sensitivity, food preferences, food choices, and nutrition status.