Sensorimotor Mechanisms Involved in Object Oriented Behaviour

Abstract

The manipulation of objects is a hallmark skill in the repertoire of human motor behaviour that involves the grasping, lifting and transporting of objects as well as movement decisions about what objects to interact with. These components of manipulation are often the focus of experiments as they offer a window into the sensorimotor mechanisms that support complex and adaptable manipulatory skill. This thesis was designed to extend the scope of object manipulation studies by focusing on functional, object oriented tasks. Three of the four studies in this thesis focus on object transport, involving reaching movements while grasping novel objects. In the first study we examined the role of haptic feedback while participants transported a non-rigid object. We showed first, the importance of haptic feedback during learning, and second, that training without haptic feedback lead to persistent deficits when subsequently performing the task after the re-introduction of haptic feedback. In a second learning study we demonstrated that kinetic errors alone are insufficient to drive the adaption of movement trajectory during learning, even in highly contextualized scenarios where the mapping of load force to motion was made apparent. In the third study, we showed that people incorporate the dynamics of the arm and object to generate grip force responses that are tuned to the change in load force during rapid, automatic arm movement responses to visuomotor perturbations. Object-oriented behaviour may also involve the linking of actions to produce an overall goal, i.e., unloading a bag of groceries is composed of numerous movements linked together. Implicit in this global task are decisions about what objects to move to and in what order. As such, in the final study, we designed a laboratory foraging task and showed that decisions about what targets to reach to were highly driven by motor factors, such as object position and size as well as cognitive factors such as value. Taken together, these studies extend the current understanding of object manipulation and offer insights into how movement factors are incorporated into decisions about what objects to move to.