Head Roll Influences on Multi-Sensory Integration for Perception and Action

Abstract

The representation of ourselves and our environment is based on the combination of information from multiple sensory systems. Each sensory modality is represented within a different frame of reference, in other words each sensory system uses a different code to represent the same properties of the environment (ex. visual stimuli in an eye-centered frame of reference; hand position would be shoulder-centered). Combing this information into a singular coordinate frame is complex. For instance, the eye and shoulder have different centers of rotation, therefore any changes in eye position or body posture will affect the relationship between them. What is still unknown is how the brain integrates these different sources of information into an internal representation, and what effect extra-retinal signals can have on this process. This thesis was designed to investigate the effect of head roll on action and perception. In Experiment 1, we wanted to determine how the integration of vision and proprioception for action was affected by changes in head roll. To investigate this question subjects performed a reaching task at three different head roll positions, where they would experience conflicts between their viewed and actual hand position. In Experiment 2, we examined the influence of head roll on sensory perception. To explore this idea subjects performed a task where they needed to judge the position of their unseen index fingertip relative to a visual target. Our findings reveal that eccentric head roll conditions influence both action and perception – revealed by an increase in movement variability and a decreased ability to discriminate the position of the unseen fingertip relative to visual targets. In summary, we have discovered that introducing eccentric head roll positions affects the perception of ourselves within the environment and the way that we integrate sensory information.