Effects of Visual and Haptic Perception of Material Rigidity on Children’s Reaching and Grasping

• In Event: Poster Session 07
  In Poster Session: PS 07 Topic - Perceptual, Sensory, Motor

Abstract

The effects of material properties on children’s reaching for objects have been rarely investigated. Although there have been studies examining infants' material-dependent object exploration, few have investigated how visual and haptic material information contributes to children’s differentiation and recognition of material rigidity for efficient and functional grasping movements. Therefore, the aim of this study was to examine young children’s unimanual reaching kinematics and grasping frequencies for objects of different material following visual and visual-haptic object exploration.
11-months-old infants, 3-year-old children and, for purposes of comparison, adults were encouraged to lift two objects while their reaching movements were measured using a quantitative motion capture system (Vicon). The objects were heavy and had two handles made out of different soft and rigid materials. In the visual condition, material rigidity was presented only visually by tapping (see Figure 1, upper panels) and pushing the handles down (Figure 1, lower panels) with a stick. In the visual-haptic condition, participants manually explored the objects and therefore gained visual and haptic material information. We expected increased grasping frequencies towards the rigid handle due to its higher functionality for lifting heavy objects.
Results showed that 11-month-olds, after visual object exploration, grasped soft and rigid handles equally often, showing no consideration of material to facilitate grasping. After visual-haptic object exploration, infants showed an unexpected, significant preference for the soft handles—which were more difficult to use to lift the object—at least when grasping the opposite-sided handle (χ²(1) = 3.96, p < .05). In contrast, adults generally grasped the rigid handle, exploiting their knowledge about efficient and functional grasping. 3-year-olds grasped soft and rigid handles equally often and therefore no longer exhibited a preference for grasping soft handles, but still no adult-like preference for rigid handles. Furthermore, reaching trajectories were only slightly affected by object rigidity, but much more substantially by visual versus visual-haptic condition and age. Visual-haptic object information led to significantly shorter reaching durations and significantly straighter hand movements compared to only visual information (p < .05). In addition, with increasing age, the number of movement units and the relative hand aperture decreased significantly, whereas movement velocity and straightness increased significantly (p < .05). In general, 11-month-olds’ trajectories still showed a lot of variability, whereas 3-year-olds’ trajectories already resembled those of adults a lot, with one MU and bell shape (see Figure 2).
Our findings suggest that material rigidity plays a minor role in infants’ grasping behavior when only visual material information is available. This indicates that infants’ reaching behavior is not guided by the functionality of the materials at 11 months. 3-year-olds seem to be on an intermediate step in the development from (1) choosing the pleasant impression of a soft fabric like the 11-month-olds, to (2) constantly choosing the efficient rigid handle like the adults. Moreover, the kinematic patterns were barely affected by rigidity, but rather by visual and haptic condition and age. This emphasizes the importance of haptic material exploration for grasping in young children.

Authors

• Lucie Preißler, Justus-Liebig-Universität Gießen
  Presenting Author

• Bianca Jovanovic, University of Giessen
  Non-Presenting Author

• Jörn Munzert, University of Giessen
  Non-Presenting Author

• Filipp Schmidt, University of Giessen
  Non-Presenting Author

• Roland W. Fleming, University of Giessen
  Non-Presenting Author

• Gudrun Schwarzer, University of Giessen
  Non-Presenting Author