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

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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.