Sensoaesthetic Properties of Materials

Our current area of research is around the area of the touch of materials. The central question in our research into the touch of materials is how the perception of materials relates to their physical properties. Our research methods contain strong elements of both psychophysics and materials science, which we use to probe both the psychological and physical aspects of touch perception.  The sense of touch is a hugely important part of our interaction with the world around us. Through touch, we can very quickly discern a lot of details about a material. The mind is like a database of sensory experiences, and as it pieces together sensory information it builds up our sensorial perceptions. This process is governed by the neurophysical make-up of your body and brain on a physical level, but your emotions and aesthetic tastes play a big part as well. In our work, we make measurements of people’s sensoaesthetic perception of a range of different materials through their sense of touch, and the results back to the core physical properties of the materials as described by materials science.

Sounds and their cultural resonances are built upon material relationships that produce specific acoustic effects and connotations. The aesthetic qualities and scientific properties of sounds and our perception of them, is key to our understanding of the world around us, and the relationships we build with materials.

To test the comparative acoustic properties of different materials we made a set of tuning forks of identical shape from varying materials. The three principle factors that influence the production of sound by a tuning fork are the shape, the density and the elastic modulus of the material from which the fork is made. The qualities of the sound produced by a tuning fork are experienced as a note of a specific pitch (frequency), with a particular brightness (a combinatory factor of duration and  amplitude). Ashby and Johnson plotted the theoretical relationship between the acoustic pitch and the acoustic brightness of a wide range of materials in their multidimensional scaling (MDS) map of acoustic properties [1].  We used the tuning forks to investigate the effects of materiality on sound, with exact frequency produced by each fork measured and the shift in pitch attributed to the change in materials. The tuning forks were also played and assessed by musicians whose perceptions of pitch and brightness were judged against those of the MDS.

In terms of the frequencies produced by the tuning forks, we found broad agreement with the theoretical predictions, apart from a few anomalies. We also found that judgements of pitch made by musicians were also in agreement with the frequency measurements. The greatest surprise was that the pitch of disparate materials could be very similar, whilst the brightness of the note varies dramatically, due to variations in materials coefficient of loss.

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[1] M. Ashby and K. Johnson, Materials and Design: The Art and Science of Material Selection in Product Design. Elsevier, 2002.

Research on the taste of materials was conducted to address the question of what physical properties of materials can be correlated with the senso-aesthetic properties that define our experience of taste.

Tastes are received through our taste buds, which are located on the upper surface of the tongue. There are five basic tastes: bitter, salty, sour, sweet, and umami, although ‘fat’ is also now becoming a candidate for distinct taste sensation. These tastes are not the only component of the sensations associated with the mouth; other important factors include smell, detected by the nose, texture detected by mechanoreceptors, and temperature, detected by thermoreceptors [1] . The chemical aspects of taste of inedible materials, such as those we considered in our experiment, are often discussed in terms of their reduction potential, in other words their susceptibility to being oxided in the mouth. These potentials have been measured for most materials, and confirm broad trends of taste, which is that metals like copper and aluminum taste strong, whereas metals gold and silver are almost tasteless (hence the high status of silverware cutlery). There are plenty of exceptions (such as titanium) and there had been no previous systematic investigation of the relation between perceived taste, and physical or chemical properties. 

With this is mind we conducted experiments in which we asked volunteers to take spoons which had been coated with seven different types of metal: zinc, copper, stainless steel, gold, tin, chrome, silver.

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 [1] B. Lindemann. Receptors and transduction in taste. Nature, 413:219–225, 2001.