Too sharp to handle: Unpleasantness from spiky object geometry in vision and touch

Humans tend to favor curved objects over sharp counterparts, yet little is known about how fine-grained geometric properties of angular surfaces influence affective evaluation across sensory modalities. We investigated how spike density, height, and thickness shape unpleasantness using 12 systematically varied 3D-printed spiky surfaces. Participants evaluated the unpleasantness under haptic, visual, and visuohaptic conditions. Linear mixed models showed that sparser, higher, and thinner spikes felt more unpleasant, with stronger effects when touch was involved. These findings demonstrate that local geometric features systematically shape feelings of the surfaces and inform the design of tactile cues and expressive haptic interfaces.