The sensible senseless person: a theoretical framework for clinical assessment of proprioception

Position-matching is a common task used to assess the sense of position, a sub-modality of proprioception. The 'sensible senseless person' (SSP), a theoretical construct that lacks sensory perception but is capable of logical inference, was developed to critically evaluate common outcome measures in such tasks. This framework reveals that traditional measures are influenced by task structure, strategic responses and the prior beliefs of the SSP. To address these limitations, we propose the Guess Index (GI), an outcome measure designed to ensure that the SSP receives the same score regardless of task or personal parameters. To demonstrate the GI's utility, we applied a simplified, clinically oriented position-matching task to healthy individuals and persons with stroke. Participants' performance often followed the SSP-predicted pattern. The GI correlated with traditional outcome measures, but was more sensitive to group differences and the only metric that classified persons with stroke above chance level in this dataset. Future studies should extend this framework to other proprioceptive sub-modalities and larger, more diverse populations before the GI can be considered a general index of proprioceptive adequacy with robust clinical cutoffs.