EXPLORING REFERENCE FRAME INTEGRATION USING THE CROSSED-HANDS DEFICIT

Abstract

You can only perceive the location of a touch when you know where your hands are in space. Locating a touch to the body requires the integration of internal (somatotopic) and external (spatial) reference frames. In order to explore the relative contribution of internal versus external information, this thesis employed a crossed-hands tactile temporal order judgment (TOJ) task. This task requires participants to indicate which of two vibrations, one to each hand, occurred first. The magnitude of the deficit observed when the hands are crossed over the midline provides an index into how internal and external reference frames are integrated. This thesis first showed that the crossed-hands tactile TOJ task is a reliable measure, supporting its use as a measure of reference frame integration. Next, this thesis applied a probabilistic model to theoretically estimate the weights placed on the internal and external reference frames. We showed that a bias towards external information results in a larger external weight and vice versa for internal information. Finally, using the model we showed that the crossed-hands deficit is reduced while lying down, supporting an influence of vestibular information on the external reference frame. Taken together, this thesis highlights that we are able to flexibly adapt the weighting of different spatial representations of touch.