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Loni Desanghere, Jonathan Marotta; Gaze strategies and grasping: Complex shapes. Journal of Vision 2009;9(8):1108. doi: 10.1167/9.8.1108.
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© ARVO (1962-2015); The Authors (2016-present)
At last year's VSS meeting (journalofvision.org/8/6/299/) we demonstrated that during a natural grasp, gaze fixations cluster towards the top edge of an object. These fixation locations were tightly coupled to index finger grasp position, which fell across the object's center of mass (COM). The tight link between grasp position and fixation locations has also been shown in situations where participants are instructed to grasp an object at a specific location (de Grave et al., 2008; Johansson et al., 2001). However, these studies have explored fixations while grasping symmetrical objects - whose COM also corresponds to the object's midline. While previous studies have highlighted the importance of an object's COM while grasping, showing that people grasp an object across this point regardless of where the midline of the object is (for example Kleinholdermann et al., 2007), it is still not clear whether such dissociations are present in gaze fixation locations.
The purpose of the present study was to explore whether it is an object's midline or an object's COM that is the main focus of fixations while grasping. Participants were presented with complex asymmetrical shapes whose COM was oriented on either the left or right side of the object's midline. In support of previous research, participants grasped the objects across the COM. Likewise, gaze fixations were concentrated towards the top edge of the objects, corresponding to index finger location. Additionally, first fixations were found to be significantly shorter in duration then final fixations, indicating that participants were spending more time looking at the shapes while positioning their fingers on the object. Despite the complexity of the shapes, however, participants did not explore the object area in more detail. This study highlights the importance of an object's COM rather than its midline for the programming of both grasp and gaze fixations.
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