Selection and Planning of Reach to Grasp Actions in the Presence of Competing Action Targets

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When planning an action there can be many objects in our environment that we can interact with. Consider meeting a friend for lunch, your water glass, your friend's glass, the ketchup bottle, the salt shaker could all be potential targets for your action. Previous research has shown that our reaching movements can veer toward or away from distracting items in our environment and we take longer to react to reach to a target in the presence of distracting items. Most of these studies however, have used pointing movements. Clearly we often need to grasp objects in the environment, but grasping may change how we want to transport our arm to the object. For instance you can point anywhere on an object, but you need to make the palm of your hand available to the object to be able to grasp it. The main goal of the proposed research is to understand how we select and plan grasping actions when there are multiple objects in our environment. The proposed research will use special cameras that record how the participant is moving their arm through space, and special gloves that can record the shape of a person's hand. In all experiments, participants will have to reach to grasp or reach to point to objects when another object is present. In the first series of experiments, participants will know what object they are supposed to reach to before they start the movement. We expect that their arm path will be affected by the non-target objects, and in particular, by non-target objects that are on the same side of the palm. In another series of experiments participants will need to start their movement before they know where the target is. Only once they start their movement will they be cued to which object is the target. This mimics how we plan our actions under uncertain conditions or when information changes in our environment. We expect that participants will plan to start their movement so their palm is available to both potential objects when they are not sure what object they will have to move to. In a final series of experiments, participants will be presented with two differently sized objects. They will have to start their movement without knowing which object will be the target. We will examine how big they open their hand and in what shape. In this series of experiments we will also be building a model that predicts what grasping shape the hand will eventually make early in the movement. The proposed research will provide new knowledge on how our brain controls the use of our arm and our hand. The model that predicts grasping movements can have applications in robotics and gesture based interfaces.