Knowing what went wrong – how do we detect motor perturbations?

• Applicant: Dr. Karl Kopiske
• Subject Area: General, Cognitive and Mathematical Psychology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 466287772

To interact successfully with a dynamic environment, we need to constantly recalibrate our actions. Even well-practiced actions are associated with error and continuously adjusted, in a process referred to as sensorimotor adaptation. Experimental research in this field frequently uses paradigms involving perturbations – that is, errors induced externally, for example through a mismatch between sensory modalities. Such paradigms have revealed that sensorimotor adaptation is often well described by simple trial-wise error correction and occurs even when we are not aware of our own errors. However, they have also shown many cases that are not as simple. For example, the relative magnitude of correction may differ by error size, or separate explicitly controlled adjustments may be made. The latter raises the question of how we become aware that we need to adjust our actions – what makes us notice perturbations or motor errors? Surprisingly, a lot remains unknown about these issues. The proposed project aims to fill this gap and investigate how inherent properties of a perturbation – specifically, its size and the sensory error signal it provides to the actor – allow humans to detect that perturbation. Grasping and walking are chosen to represent typical human actions in the experimental investigations. First, the relation between the visual and haptic size of a graspable object will be varied and the magnitude and the functional form of this variation manipulated. Second, analogous variations will be applied to the speed of two belts of a split-belt treadmill during walking. Grasp and gait parameters will be measured to quantify sensorimotor adaption – of grasping and gait, respectively – and simultaneously perceptual judgements about the perturbation will be recorded. This will allow us to quantify the relative contributions of perturbation size and sensory error signal to perturbation detection and to sensorimotor adaption. During the described measurements, participants’ pupillary size will be continuously recorded. Pupil size constitutes a potential no-report marker of perturbation detection, having been shown to correlate with unexpected events and with cognitive load in motor tasks. If pupil dilation varies systematically with the perturbation and its detection, it may become useful as a physiological marker to validate psychophysical responses. Thus, this project aims to fill the gap of psychophysical data on perturbation detection and work towards an objective physiological marker of it. The insights gained from the project will provide an important step towards understanding the role of awareness of perturbations in sensorimotor adaptation. On a larger scale, they will help us understand the mechanisms of how humans so readily adapt to the complex motor demands of everyday activities.

• DFG Programme: Research Grants