The role of differential delays in integrating transient visual and proprioceptive information

Abstract

Many actions involve limb movements toward a target. Visual and proprioceptive estimates are available online, and by optimally combining (Ernst and Banks, 2002) both modalities during the movement, the system can increase the precision of the hand estimate. The notion that both sensory modalities are integrated is also motivated by the intuition that we do not consciously perceive any discrepancy between the felt and seen hand's positions. This coherence as a result of integration does not necessarily imply realignment between the two modalities (Smeets et al., 2006). For example, the two estimates (visual and proprioceptive) might be different without either of them (e.g., proprioception) ever being adjusted after recovering the other (e.g., vision). The implication that the felt and seen positions might be different has a temporal analog. Because the actual feedback from the hand at a given instantaneous position reaches brain areas at different times for proprioception and vision (shorter for proprioception), the corresponding instantaneous unisensory position estimates will be different, with the proprioceptive one being ahead of the visual one. Based on the assumption that the system integrates optimally and online the available evidence from both senses, we introduce a temporal mechanism that explains the reported overestimation of hand positions when vision is occluded for active and passive movements (Gritsenko et al., 2007) without the need to resort to initial feedforward estimates (Wolpert et al., 1995). We set up hypotheses to test the validity of the model, and we contrast simulation-based predictions with empirical data.

Cerebellar patients have intact feedback control that can be leveraged to improve reaching

“…The model merges the cascade of the subject’s internal controller and mechanical plant (arm and robot dynamics); the combined plant and controller is treated as a classic McRuer gain-crossover model—a scaled integrator—a model based on the assumption that the subject is responding to an unpredictable stimulus (McRuer and Krendel 1974). Our hypothesis is that all model parameters would be equivalent between patients and age-matched controls, except that patients would have a feedback delay commensurate with their visual processing time (∼140-250 ms) and controls would have a lower-latency feedback delay commensurate with their proprioceptive feedback processing time (∼110-150 ms) (Cameron, de la Malla, and López-Moliner 2014; N. H. Bhanpuri, Okamura, and Bastian 2013). This is because we expect that patients would rely more on (slower) visual feedback to compensate for their deficient estimation of limb state.…”

Target modality affects visually guided online control of reaching

“…During movement, velocity changes are considerably larger in the amplitude dimension of the reach than in the direction dimension. It is possible that proprioception, with a shorter processing time than vision, provides a more up-to-date estimate of hand position than vision does (Cameron, de la Malla, & López-Moliner, 2014). Accordingly, proprioception may be more heavily weighted in the dimension of the reach that is associated with the highest velocities.…”

Supplemental vibrotactile feedback of real-time limb position enhances precision of goal-directed reaching

“…These sensation deficits contribute to impaired control of reaching and stabilization behaviors that are vital to an independent life style (Blennerhassett et al, 2007;Scheidt and Stoeckmann, 2007;Tyson et al, 2008;Zackowski et al, 2004). Although such individuals often rely on visual feedback to guide movement, lengthy delays of visual processing (100-200 ms; (Cameron et al, 2014) yield slow, poorlycoordinated actions that require focused attention Sainburg et al, 1993); visually guided corrections come too late and result in jerky, unstable movements (Sarlegna et al, 2006). Several research groups have proposed technological solutions to problems caused by somatosensory deficits,…”