Sensitivity to viscosity changes and subsequent estimates of satiety across different senses.

While it is widely accepted that texture is a multimodal in nature, little research has been published regarding how we use senses other than touch to assess texture. In beverages, humans use texture (i.e. viscosity) information to estimate calories and expected satiety. This study was designed to compare and contrast the sensitivity of humans to changes in viscosity and their ability to estimate satiety through different sensory modalities. Milk samples of varying viscosities were constructed, and 49 participants were asked to perform a series of 2-alternative forced choice tests and identify which sample was thicker. Sensitivity to viscosity changes across different sensory modalities was determined by having each participant consume the samples, listen to the samples pouring, and observe clear vials of the samples. Using vision, participants were notably less sensitive to changes in viscosity when compared to hearing or oral tactile sensations. Interestingly, oral tactile sensations and hearing were almost identical in their viscosity difference thresholds (0.346 cP and 0.360 cP, respectively). Similar patterns were observed when the participants were asked to estimate how full they expected to be after consuming beverage stimuli varying in viscosity. Expected caloric values and satiation were found to change with thickness level when participants were assessing the stimuli through the auditory or tactile modalities. However, these measures of expected caloric value and satiation did not change as a function of viscosity for visual assessment, suggesting the assessment of caloric density and satiation are linked to specific sensory modalities' ability to detect viscosity. This study highlights the relative importance of vision, auditory, and touch to forming our sensory judgements regarding viscosity and subsequent satiety estimations.