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Martin Giesel, Karina Kangur, Julie M. Harris, Constanze Hesse; Investigating the influence of surface properties on reaching movements. Journal of Vision 2019;19(10):252a. doi: 10.1167/19.10.252a.
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We used an obstacle-avoidance paradigm to investigate how surface properties of obstacles affect hand movements in a reaching task. The obstacles’ surfaces were made from five different materials (wood, sandpaper, sugar granules, rock salt, Astro Turf). All obstacles had the same shape, size and colour, but their surface textures differed in granularity, density and height. An auditory cue signalled participants to reach in-between two obstacles either to the upper or lower half of a target area that was located 40 cm away from the start position of the movement. Obstacles were placed midway between start position and target area to the left and right of the movement path. In each trial, one of the obstacles was always the smoothest obstacle (baseline obstacle, i.e., wood) while the other was one of the five obstacle types. Obstacle types, obstacle positions, and cued end location were presented interleaved and in pseudo-randomised order. Vision between trials was occluded using shutter glasses and hand movements were recorded using an electromagnetic motion tracking system. After the reaching task, participants rated the roughness, smoothness and pleasantness-to-touch of each obstacle. We analysed the differences between movement trajectories depending on the position of the baseline obstacle (left or right) using three parameters: the area under the trajectory, the lateral position of the hand between the obstacles and at the end of the movement. All parameters were computed relative to the baseline condition, in which the baseline obstacle was presented on both sides. We found a significant position shift for all three parameters indicating that participants moved their hands closer to the baseline obstacle (i.e., away from other obstacles). The strength of this shift was positively correlated with the roughness ratings of the obstacles. These findings provide proof-of-concept for the use of behavioural measures of material properties.
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