Taking the rough with the smooth: aging effects on tactile surface texture perception

Over the course of a day most of us handle numerous items, grasping and manipulating them, at the same time running our hands and fingers over their surfaces. Sometimes we touch and handle objects that are fully visible in order to carry out a particular task, for instance, picking up money from a countertop. At other times we may seek to identify an object, or some part of it, by its shape or surface texture when it cannot be seen, for example, when trying to retrieve money in a wallet. The sensations evoked by touching surfaces (e.g. smooth vs. textured, soft vs. hard, sticky vs. slippery) and the effect of products that change the feel of touched objects (e.g. in washing dishes, fabrics, hair) can be key to their usability and commercial success.
Despite the importance of surface feel, only now are we beginning to understand how humans explore surfaces, what is the physics of the interaction between finger and surface, what is the information that receptors in skin and muscles capture about surface texture, and how surface sensations are affected by multisensory signals. Recent neuroscientific studies, including research in our lab, indicate how, not only brain areas that respond to touch are involved in texture perception, but also regions that primarily process visual and auditory information contribute to texture perception, even in the absence of visual and auditory stimuli. These findings help our understanding of previous research showing that the feel of a touched surface can be influenced by concurrent sounds and images.
Surface exploration is an active process that may involve static or dynamic touching with the finger tip pressing (e.g. to determine hardness or temperature) or sliding (e.g. to determine roughness or stickiness) over the surface. In either case, good control of finger tip movement (position and force) is required, along with suitable cognitive resources to define exploration strategies appropriate to the surface possibilities. Given a number of touch components, each liable to variability or 'noise', are involved in active touch for surface perception, this can lead to deterioration in overall performance if, as is likely, the noise increases with age. On the other hand, redundancy may contribute to substitution of one process for another (or a change in their relative weighting), which can reduce the impact of deterioration in one or more of the components. Aging touch is therefore of both theoretical and practical importance in understanding touch.
In this project the Universities of Birmingham and Nottingham have come together with Procter & Gamble to understand how information from touch is actively generated, processed and combined with information from other senses (hearing, vision) and how these processes change later in life. Research into aging effects on perception has largely focused on vision and hearing. However, age-related changes in both peripheral and central aspects of touch have been observed. This project includes behavioural and brain imaging studies of active touch to develop a model of how information is actively sought and combined to sense texture and how these processes are adjusted to compensate for age-related changes. Furthermore the findings and model will be extended to a consumer product-testing environment to examine the effects of cleaning products on tactile surface perception.
In summary, the ways in which we use active touch to perceive surface texture are not fully understood and the effects of aging are relatively unknown. The proposed project addresses these topics by detailing surface perception on a wide scale (ranging from smooth surfaces to relatively coarse surfaces made of gratings with lines spaced hundreds of microns apart and including naturally occurring and manufactured surfaces with various coatings affecting frictional resistance to sliding) using behavioural, brain imaging and modeling approaches in healthy young and aging populations.

The proposed project is a collaboration involving expertise in academia and industry to understand how information from multiple sources and senses is combined to perceive surface texture and how this process changes with age. Different textures, including roughness (ranging over smooth, fine, coarse) and surface friction (ranging from slippery to sticky), are known to be perceived via a combination of tactile and proprioceptive information mediated by receptors in skin and muscle. However, there is no formal model of how movement, tactile and proprioceptive inputs are integrated. Moreover, little is known about how other sensory cues contribute to the final percept, despite recent compelling evidence that touch is a multisensory experience that changes throughout the lifespan. This project combines behavioural and brain imaging experiments to relate changes in tactile surface perception with age to changes in skin biomechanics and to develop a Bayesian model of texture-based perceptual decisions. The model will be extended to a consumer product-testing environment to measure how texture is used to judge cleanliness in dish washing.
Three partners, Universities of Birmingham and Nottingham and Procter & Gamble, will take part in 3 work packages. WP 1 will measure the behavioural effects of varying texture stimuli on older and younger adults' performance on perceptual decisions. This will be the first step towards a model of the factors influencing texture perception. WP 2 will measure neural activity in brain regions selective for touch, auditory and visual stimuli as well as in 'higher' cognitive regions. This will allow us to understand the level of multisensory influence on texture perception, and if this varies as sensory abilities change with age. WP 3, will assess how texture perception is related to concepts of cleanliness and washing in order to evaluate how well our models generalize to everyday situations and product development.

Procter & Gamble (P&G) has a formal collaboration with the University of Birmingham in the area of product formulation and engineering. Formulated products contain a wide range of different active ingredients that can interact with each other in a synergistic or detrimental manner. The products' chemistry, in conjunction with the processing of the product is what ultimately determines the products' chemical and physical properties and the consumer's perception when using a product or interacting with surfaces treated with the product. Understanding the process of how the consumer interacts with the products and the surfaces on which the products act is therefore seen as critical by P&G as they seek to optimize product design for consumer benefit. The proposed research area opens up a novel opportunity for collaboration with psychologists at Birmingham and Nottingham, which can help P&G in correlating how product characteristics are perceived by the product user's senses, especially touch. Thus, a major impact of this project will be commercial, with important additional impact envisaged in health/clinical settings and in public engagement and information.
Industrial/Economic:
Dish washing. We expect a direct contribution to product design and improvement from the understanding of the consumer experience of using washing products, in terms of product design (given improved understanding of touch sensing abilities) in order to supplement the designer's traditional mix of implicit knowledge and inspiration. The chosen target for short and medium term impact is via hand dishwashing liquid. Active touch is used every day to assess dirt or grease (consider running your finger over a shelf, or plates in the washing up). Cleanliness of dishes is important, both for those living independently, but also for those living in supported or cared for environments. As touch declines with age, it may be increasingly difficult to discriminate surface cleanliness with touch and there may be an increased reliance on vision to compensate. Products and strategies can be designed to 'fit' with these changes. The improvement of food preparation surface and eating utensil cleanliness is particularly critical in healthcare or nursing settings but also in the home. Improvements in the ease of cleaning would reduce costs for healthcare and improve well-being.
Coping with aging effects on touch. The effects of aging on active touch are not well understood. The methods for studying active touch developed in the project and the findings about aging effects on skin biomechanics and multisensory integration for surface perception will be explored with stakeholder groups including those working in elderly product design, for example, developing skin creams to help with skin hydration. Increasing the understanding of normal capacity and changes with age will also have implications for assessment in diagnosis and treatment of diseases affecting touch including peripheral vascular problems (eg diabetes), and disorders of the central nervous system (eg stroke). The incidence of many of these diseases increases with age so understanding the typical ranges of performance will aid in identifying the non-typical individual. Furthermore this will also aid in the planning of rehabilitation for those with impairments, for instance by encouraging use of alternate sensory information or different movement patterns in activities of daily living.
Public awareness.
There is general awareness of the decline of vision (at least to the extent of increased spectacle use) or hearing (hearing aids), but there is little knowledge of the typical decline of touch. Many older people will experience declines in tactile sensitivity so it may be helpful and reassuring, both to them and their carers, to understand normal changes that occur with aging and it may be useful to understand the role of the other senses in reducing the impact of the changes in touch.