How Shape and Material Properties Affect Touch Patterns During Complex Shape Perception

Shape perception through touch allows object recognition without visual input. While humans can reliably perceive and discriminate geometric features like curvature, less is known about how perceivers explore and integrate these features to form coherent shape representations when perceiving complex shapes through touch. Here, we investigated whether individuals prioritise certain shape features when gathering information about complex shapes. We compared touch patterns for convex, concave and flat regions, when exploring shapes varying in material properties (rigid-plastic vs. deformable-silicone) and shape features (convex, concave and flat). Participants explored one reference and two test objects using a finger and selected the test object that was most similar in shape to the reference. We assessed dwell time, distance travelled, velocity, and force of touch. Across the two materials, exploration parameters were generally consistent, except that participants applied less force to deformable shapes. For both materials, participants showed a clear preference for exploring concave over convex or flat regions indicated by all parameters, suggesting that these regions were considered as more informative and formed an important basis of their shape judgments.