Assessment of Spatial Lingual Tactile Sensitivity using a Gratings Orientation Test

Summary

This work illustrates a standard procedure and threshold determination by the R-index to assess spatial lingual tactile sensitivity using a gratings orientation test.

Abstract

Individual thresholds by R-index estimates are calculated using a gratings orientation test (6 different tools of increasing grating size from 0.20-1.25 mm) to assess spatial lingual tactile sensitivity. During the experiment, the subjects are blindfolded and asked to specify the orientation of the grating (either horizontal or vertical) placed on the tongue. R-index is based on Signal Detection Theory (SDT), and it is an estimated probability of correctly identifying a target stimulus (the signal, e.g., the correct orientation) compared to an alternative stimulus (the noise, e.g., the incorrect orientation). Once the R-index values for each subject and each tool dimension are calculated, it is possible to derive the individual threshold by interpolating the two R-indices immediately below and above the established cut-off (typically 75%) based on one-sided R-index critical values. This procedure can be helpful in the medical field to study the association between oral tactile sensitivity, speech clarity, and swallowing disorders, as well as in sensory and consumer studies to explore individual variation in texture perception, food preferences, and eating behavior.

Introduction

The texture and mouthfeel of food play an important role in liking^1,2,3,4, and while research has found differences in texture perception due to factors such as chewing behavior^2,5, saliva flow, and composition^6,7, there are limited methods available to assess variation in oral tactile receptors (mechanoreceptors). The oral cavity houses different types of mechanoreceptors found in the mouth: Merkel receptors,....

Protocol

An informed, written consent has been signed by all participants. This study was approved by the Ethics Committee of the University of Milan (n. 48/19) and conducted in accordance with the Declaration of Helsinki.

1. Training of experimenters

1. Take the grating tool and apply a force of 100 g on a sponge placed on a scale.
   NOTE: Refer to Figure 1 for the schematic of the grating tool used in this study
2. Repeat this procedure at least 10 times to reduce variation in the force applied by the grating on the subjects' tongues during testing, both within and across experimenters.

<....

Results

A total of 70 healthy adults (age range = 19-33 years; mean age = 22.0; 52.9% women) were involved in the study, as shown in Appiani et al. (2020)²¹.

As an example, the R-index distribution by age for square 0.75 mm is reported in Figure 4. Each point represents a different subject. Subjects above the dotted line (cut-off value: 0.7426) are those who correctly identify the orientation of the grating (more sensitive).

Discussion

Few valid instruments are available for measuring tactile acuity^10,11,13,22. Von Frey filaments have been shown to be an adequate method for measuring both skin and oral tactile acuity^10,21,22. However, these instruments measure a different dimension of lingual tactile acuity than the gratings orientat.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Custom-made squares	University of Reading; University of Copenhagen		Squares of 1 cm2 from polytetrafluoroethylene (PTFE)
Disinfenctant solution (20% sodium hypochlorite)	Amuchina, Angelini S.p.A., Roma, Italy
Eye masks	Various
Gloves	Various
Lab coat	Various
Plastic cup for drinking water	Various
Excel	Microsoft