title: Predicting the effect of surface texture on the qualitative form of prehension.
abstract: Reach-to-grasp movements change quantitatively in a lawful (i.e. predictable) manner with changes in object properties. We explored whether altering object texture would produce qualitative changes in the form of the precontact movement patterns. Twelve participants reached to lift objects from a tabletop. Nine objects were produced, each with one of three grip surface textures (high-friction, medium-friction and low-friction) and one of three widths (50 mm, 70 mm and 90 mm). Each object was placed at three distances (100 mm, 300 mm and 500 mm), representing a total of 27 trial conditions. We observed two distinct movement patterns across all trials--participants either: (i) brought their arm to a stop, secured the object and lifted it from the tabletop; or (ii) grasped the object 'on-the-fly', so it was secured in the hand while the arm was moving. A majority of grasps were on-the-fly when the texture was high-friction and none when the object was low-friction, with medium-friction producing an intermediate proportion. Previous research has shown that the probability of on-the-fly behaviour is a function of grasp surface accuracy constraints. A finger friction rig was used to calculate the coefficients of friction for the objects and these calculations showed that the area available for a stable grasp (the 'functional grasp surface size') increased with surface friction coefficient. Thus, knowledge of functional grasp surface size is required to predict the probability of observing a given qualitative form of grasping in human prehensile behaviour.
authors.affiliation: Institute of Psychological Sciences, University of Leeds, Leeds, West Yorkshire, United Kingdom.
authors.forename: Ian John
authors.initials: IJ
authors.lastname: Flatters
authors.forename: Loanne
authors.initials: L
authors.lastname: Otten
authors.forename: Anna
authors.initials: A
authors.lastname: Witvliet
authors.forename: Brian
authors.initials: B
authors.lastname: Henson
authors.forename: Raymond John
authors.initials: RJ
authors.lastname: Holt
authors.forename: Pete
authors.initials: P
authors.lastname: Culmer
authors.forename: Geoffrey Parker
authors.initials: GP
authors.lastname: Bingham
authors.forename: Richard McGilchrist
authors.initials: RM
authors.lastname: Wilkie
authors.forename: Mark
authors.initials: M
authors.lastname: Mon-Williams
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D017276:Friction; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology; D013499:Surface Properties; D055815:Young Adult