A review on oral tactile acuity: measurement, influencing factors and its relation to food perception and preference

Relationship between texture perception and oral function: A preliminary study in young, healthy adults

BACKGROUND

Oral frailty, characterised by reduced oral function, is associated with systemic health issues in older adults. Although the criteria for diminished oral function often focus on motor and secretory abilities, texture perception also plays a crucial role in health due to its impact on food intake and palatability.

OBJECTIVE

This study aimed to explore the relationship between thickness discrimination ability (TDA) and oral motor and secretory functions in healthy young individuals.

METHODS

Twenty-eight adults were assessed for texture perception using eight concentrations of aqueous xanthan gum solutions to determine TDA scores. Measurements of occlusal force, masticatory performance, tongue pressure, stimulated salivary flow rate and tongue-lip motor function were conducted. Spearman's correlation analysis was used to evaluate the relationship between TDA scores and oral functions. Participants were divided into high-sensitivity and low-sensitivity groups based on their TDA scores to compare oral function test results.

RESULTS

The TDA scores varied among the participants, with higher scores correlating with higher masticatory performance (r = 0.41, p < .05). Masticatory performance in the high-sensitivity group was significantly higher than in the low-sensitivity group (211.9 ± 59.2 mg/dL vs. 157.9 ± 43.0 mg/dL, p = .013), with no significant differences in other oral functions.

CONCLUSION

Masticatory performance was correlated with TDA, suggesting a link between the selection function of mastication and thickness discrimination. These findings highlight the potential relevance of texture perception in oral function and indicate the need for further exploration, particularly in older adults with declining oral health.

The Feel of Speech: Multisystem and Polymodal Somatosensation in Speech Production

PURPOSE

The oral structures such as the tongue and lips have remarkable somatosensory capacities, but understanding the roles of somatosensation in speech production requires a more comprehensive knowledge of somatosensation in the speech production system in its entirety, including the respiratory, laryngeal, and supralaryngeal subsystems. This review was conducted to summarize the system-wide somatosensory information available for speech production.

METHOD

The search was conducted with PubMed/Medline and Google Scholar for articles published until November 2023. Numerous search terms were used in conducting the review, which covered the topics of psychophysics, basic and clinical behavioral research, neuroanatomy, and neuroscience.

RESULTS AND CONCLUSIONS

The current understanding of speech somatosensation rests primarily on the two pillars of psychophysics and neuroscience. The confluence of polymodal afferent streams supports the development, maintenance, and refinement of speech production. Receptors are both canonical and noncanonical, with the latter occurring especially in the muscles innervated by the facial nerve. Somatosensory representation in the cortex is disproportionately large and provides for sensory interactions. Speech somatosensory function is robust over the lifespan, with possible declines in advanced aging. The understanding of somatosensation in speech disorders is largely disconnected from research and theory on speech production. A speech somatoscape is proposed as the generalized, system-wide sensation of speech production, with implications for speech development, speech motor control, and speech disorders.

The impact of temperature and a chemesthetic cooling agent on lingual roughness sensitivity

Oral tactile sensitivity underpins food texture perception, but few studies have investigated mechanoreception in oral tissues. During food consumption, oral tissues are exposed to a wide range of temperatures and chemical entities. The objective of the present study was to assess the influence of thermal sensations on lingual roughness sensitivity. Just-noticeable difference thresholds (JNDs) were determined using the staircase method for surface roughness from stainless steel coupons (Ra; 0.177-0.465 µm). Thresholds were assessed when cooling or heating the metal stimuli (n = 32 subjects). Compared to the JND threshold obtained at an ambient stimulus temperature (21 °C: 0.055 ± 0.010 μm), a cold (8 °C) temperature significantly (P = 0.019) reduced tongue sensitivity (i.e. increased JND) to surface roughness (0.109 ± 0.016 μm, respectively) whereas warm and hot temperatures had no significant effect (35 °C: 0.084 ± 0.012 μm; 45 °C: 0.081 ± 0.011 μm). To assess whether the effect of cooling on roughness thresholds is TRPM8-dependent, we collected roughness thresholds in a second cohort of subjects (n = 27) following the lingual application of the cooling compound Evercool 190 (24.3 µM). Interestingly, when Evercool 190 was used to elicit the cold sensation, lingual roughness JNDs were unaffected compared to the control application of water (EC: 0.112 ± 0.016 μm; water: 0.102 ± 0.017 μm; P = 0.604). That lingual roughness sensitivity is decreased by cold temperature, but not chemicals evoking cold sensations, suggests the mechanism underpinning thermal modulation is not TRPM8 dependent.

Effect of texture preference on food texture perception: Exploring the role of matching food texture and preference

This study aimed to investigate the influence of smooth texture preference on smoothness perception. An online questionnaire (Study 1, n = 464) and a sensory evaluation test (Study 2, n = 65) were administered to Japanese elderly participants (65-74 years), with common Japanese confectionery (Daifuku) as test foods. Through the online questionnaire, four distinct texture preference groups were formed based on the factors of preference for smoothness and firmness of the inner bean paste layer. Analysis of the food preference scale for imbalanced diet (FPSID) revealed that smooth-texture likers were more likely to be picky eaters than firm-texture likers. Furthermore, high (HiSm) and low smoothness preference groups (LoSm) were selected for the food sensory evaluation test to compare perceived textures (smoothness and firmness). Only the HiSm group exhibited a positive association between perceived smoothness and overall texture liking, perceiving smoothness significantly more intense than the LoSm group in situations where overall texture liking was high. This finding indicates that smooth texture preference does not act independently but rather interacts with food texture matching to affect perception. Our findings suggest that when food texture aligns with individuals' preferences, it elicits hedonic emotions and dynamically enhances food texture perception. This preference-involved perceptual process may contribute to the development of more explicit texture preferences.

Methodological approaches to assess tactile sensitivity in the food context-A scoping review

In contrast to taste sensitivity, the assessment of texture or tactile sensitivity has received relatively little attention in the food context. Texture plays an important role in food preferences and food intake, and individual differences make it important to understand physiological drivers of perception as tactile sensitivity. The multi-dimensional and dynamic aspects of texture perception suggest there is not one single method that can explain individual differences. This scoping review aims to systematically map methods assessing tactile sensitivity, in the context of food, highlighting differences in approach and implementation. Eligibility criteria included papers describing methods to assess individual differences in tactile sensitivity, that involved human participants and the context was relevant to food behavior. Sources are peer-reviewed publications of original research in English. In mapping the methods, we assessed how they relate to food texture parameters (mechanical, geometrical, and surface) and the dynamics of breaking down (touch with hand, first bite/sip, oral processing, residual or after-swallowing sensations). We also review other parameters associated (oral processing, preference, diet and food intake behavior). The literature in this relatively young area is still very fragmented and it is difficult to have a clear picture regarding best practices or recommendations for the measurement of tactile sensitivity in the food context. Future studies should aim to methodological harmonization for application in the food behavior area, with a design of experiment combining different aspects of tactile sensitivity to food, focusing on the thresholds and perceived intensity of textural parameters as well as affective and behavioral responses, and covering the whole spectrum of tactile texture perception (mechanical, geometrics, and surface), including the dynamics of perception.

A review on children's oral texture perception and preferences in foods

Texture properties of foods are particular drivers for food acceptance and rejection in children. The texture preferences follow the developmental progression of the child and these changes modulate the present and future food habits. This paper reviews the development and factors influencing texture preferences in children and the methods in food texture research with children. The child's acceptance of more complex food textures is age-dependent. The progression is indorsed by the development of oral processing skills at an early age and bolstered by repeated exposures to foods with varying textures. Children generally reject foods containing pieces or bits (i.e., geometrical textural properties); however, the impact of mechanical textural properties on food acceptance is less clear. Child characteristics such as food neophobia, picky eating, and tactile over-responsivity, negatively affect the acceptance of more diverse food textures. Depending on the child's age, the prevailing methods of characterizing food texture preferences in children include observational techniques and self-reported questionnaires. Despite knowledge of children's development of masticatory skills, learning, and cognitive abilities, the relationships of these changes to food texture acceptance and the recommended test methodology for evaluating product texture acceptance in this period of life are still limited.