Not quite…This research article is not in disagreement that visual reference can provide a compensatory mechanism, in fact in the discussion it explicitly states that “visual information might help reduce FOG”. However, We think the reader may be missing the most important finding, that is, in visually IDENTICAL conditions FRAME (Dark) and NO FRAME (Dark), there is a drastic increase in the number of FOG episodes experienced – this is in fact the most interesting finding. In the comment above, it was mentioned that vision may be a compensatory mechanism, and we agree… BUT the question should be for what? Compensation for other sensory deficits? Attentional deficits? Cognitive decline?

Based on our results we might argue that PD-FOG are compensating for an impairment in utilization of proprioception and hence the ability to make sense of one’s self-motion. Thus, when patients have to rely on only proprioception (because vision isn’t available) to navigate towards a potentially threatening obstacle, the system may “freeze” because the sensory feedback may not suffice. IF FOG is a result of poor processing or integration of sensory feedback (primarily proprioception), we should start to re-evaluate why certain situations provoke FOG (ex. passing through doorways), and whether updating self-motion information is critical in these different situations?

Additionally, when vision is available, do PD-FOG use vision and down-weight proprioception in order to minimize (or compensating for) this deficit? We would argue that this is the case, when patients are required to navigate into open space in the dark -- accurate self-motion information might not be essential -- thus less FOG episodes are provoked. Although there are many hypotheses surrounding FOG, it is critical to consider how sensory processing or integration might be the underlying factor that explains all of these other theories?