The influence of thermal, tactile and visual modalities on human skin wetness perception

Wetness perception is the ability to sense wet stimuli in the surrounding environment and is a critical skill for species across the animal kingdom. It plays a key role in survival and experience, underpinning a range of homeostatic processes and driving many comfort responses. Experiences can range from small interactions such as touching damp fabrics to full body experiences such as swimming. In each case, the human brain must account for several different senses, including the appearance and sensation of what they are interacting with. The way the brain uses these cues to form a coherent overall picture is called multisensory integration. Across four studies, this thesis builds upon previous work by further investigating the sensory experience behind wetness perception. It focusses on the role of different senses and how they affect wetness perception both individually and together, and to what extent. This has a fundamental relevance as it will aid the understanding of the physical and psychological processes that underpin wetness perception and give insight into the wider multisensory mechanisms that function across the brain. This knowledge will also be used to improve the design of absorbent hygiene products, aiming to improve the experience of both wearer and caregiver.

The first study focussed on finding the minimum amount of wetness that can be sensed by the human index fingerpad, and how a range of different wetness temperatures may impact this. The relative wetness detection threshold was found to be 1.93 x 10-4 ml mm-2 at a neutral skin temperature using absorbent stimuli. Thresholds were lowered by cold temperatures and raised by warmer temperatures, which shows that cold sensations illicit greater wetness perception. However, the volume of liquid still effects wetness perception more than its temperature. The second study focussed on the influence of physical and mechanical properties on wetness perception. Wetness perception was most influenced by coefficient of friction, contact surface area and arithmetic roughness, Ra. The third study investigated visual stimuli in-situ, finding that participants could determine if a stimulus was dry or wet in visual only conditions, but were also able to discriminate between different magnitudes of wetness during visuotactile conditions. Greater stain chroma resulted in increased wetness perception, but stain size did not have an effect. While results show that visual cues influence wetness perception, they indicate that visual dominance does not apply in these sensory integrations. The fourth study was conducted online, also focussed on vision. It showed that ex-situ wetness perception shares a positive relationship with stain chroma and size, and varies with stain hue such that higher wavelengths result in greater wetness perception. These studies collectively advance the knowledge of the importance of three sensory modalities involved in wetness perception, and can be used to inform the design of products with moisture management properties. Further studies should focus on additional sensory modalities, such as the influence of auditory and olfactory cues on wetness perception. This may give insight into associative perceptions and could be used to build the most thorough understanding of multisensory integration of wetness perception to date.