Roughness or sliminess: What makes a haptic material unpleasant

The current study aims to identify materials that most people experience as being unpleasant to touch and to uncover the perceptual attributes that link to unpleasantness. We sampled 79 everyday materials covering a wide range of sensory properties such as fluidity, granularity, roughness, and softness, e.g., cooking oil, sand, coconut, and silk. We asked participants to freely explore these materials with their dominant hand and subsequently rate their unpleasantness and 23 sensory attributes (e.g., elasticity, stickiness) in the absence of visual and auditory feedback. We collected data on material unpleasantness from two populations: Germany and the UK. Our wide array of materials showed different unpleasantness levels that correlated with specific perceptual material attributes. In general, viscous and deformable materials (e.g., hair gel, play-doh) felt more unpleasant to touch than surface-soft and smooth materials. Results were comparable for the German and UK samples. Overall, our results revealed a relationship between specific sensory attributes of materials and their unpleasantness, which seems to be consistent across German and UK samples. Our findings contribute to the understanding of how various sensory attributes are related to haptic unpleasantness. These insights advance our understanding of haptic perception with various implications, such as product design and affective computing systems, as both seek to integrate touch for detecting and modulating human affective states.