Emotional and sensory characterization of thermoplastic surfaces with different roughness

Abstract Design of products involves functional and sensory aspects, where surfaces play an important role. This study uses (i) sensory attributes to show that tactile sensation is highly dependent on surface roughness, and (ii) variation in pupil diameter to suggest that roughness close to fingerprint geometry causes less arousal. A panel of over 30 participants explored six plexiglass surfaces with different roughness generated by variations in milling speed and depth. The pattern obtained on the samples is periodic in one direction, with an average wavelength between 113 μm to 600 μm and an average height between 13 μm and 123 μm. During a blind touch, the sensory attributes of smoothness, grip and quality of each sample were evaluated by the panellists, as well as the emotional attributes of valence and arousal. The evolution of pupil diameter over time was also recorded, and its average value during the first two seconds of touch was considered as a new emotional attribute. These attributes made it possible to calculate six centred indicators, ranging between −1 and 1, for each panellist and each sample. Statistical analysis of these indicators showed that the declared valence is correlated with smoothness, grip, and quality, all gradually decreasing as roughness increases. These results will allow product designers to improve the hedonic experience of future users. To more precisely analyse arousal, valence, and the evolution of pupil diameter, three of the six samples, manufactured with the same cutting tool, were considered. Valence and arousal appeared relatively difficult to verbalised, but the pupil diameter allowed the samples to be discriminated. The sample with a roughness close to the geometry of the fingerprint appeared to be the least emotional.