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Brad Kempster, Claudia Gonzalez; Left hemisphere advantage in the visual processing of graspable objects. Journal of Vision 2011;11(11):830. doi: 10.1167/11.11.830.
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n a series of grasping studies using visual illusions we showed that regardless of handedness, right hand but not left hand grip apertures are accurately scaled to the size of an object. Grip apertures in the left hand, reflected the perceived (illusory) and not the real size of the target (Gonzalez et al., 2006, 2008). We advanced the hypothesis that the left hemisphere is specialized for visually-guided grasping and that this specialization was independent of handedness. Grasping requires the integration of a visual and a motor component, however. Here we investigate if there are hemispheric asymmetries in encoding visual properties of objects that could later explain the left hemisphere/right hand advantages in visually-guided grasping. We presented pictures of graspable objects, defined as objects that could be picked up with one hand (e.g. coin, apple, etc) and non-graspable objects, defined as tangible objects that could not be picked up with one hand (i.e. car, piano, etc) selectively to the right (RVF) or left (LVF) visual fields. Graspable/non-graspable objects and RVF/LVF presentation were randomized over the trials. Right- and left-handed participants quickly pressed a button with the index finger if the object on the screen was of a graspable object and pressed a different button with the middle finger if it was of a non-graspable object. Responding fingers and starting hands were counterbalanced among participants. Overall, reaction times were shorter for graspable objects than for non-graspable objects. Furthermore, there was a RVF (left hemisphere) advantage (shorter reaction times) but only for graspable objects. No visual field difference was detected for non-graspable objects. These findings were the same for right and left-handers. The results strongly suggest that the processing of graspable objects regardless of handedness is more efficient in the left hemisphere and this might help explain asymmetries in visually-guided grasping.
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