Integration of anatomical and external response mappings explains crossing effects in tactile localization: A probabilistic modeling approach

Abstract

To act upon a tactile stimulus its original skinbased, anatomical spatial code has to be transformed into an external, posture-dependent reference frame, a process known as tactile remapping. When the limbs are crossed, anatomical and external location codes are in conflict, leading to a decline in tactile localization accuracy. It is unknown whether this impairment originates from the integration of the resulting external localization response with the original, anatomical one or from a failure of tactile remapping in crossed postures. We fitted probabilistic models based on these diverging accounts to the data from three tactile localization experiments. Hand crossing disturbed tactile left-right location choices in all experiments. Furthermore, the size of these crossing effects was modulated by stimulus configuration and task instructions. The best model accounted for these results by integration of the external response mapping with the original, anatomical one, while applying identical integration weights for uncrossed and crossed postures. Thus, the model explained the data without assuming failures of remapping. Moreover, performance differences across tasks were accounted for by non-individual parameter adjustments, indicating that individual participants' task adaptation results from one common functional mechanism. These results suggest that remapping is an automatic and accurate process, and that the observed localization impairments in touch result from a cognitively controlled integration process that combines anatomically and externally coded responses.

A three-dimensional spatial characterization of the crossed-hands deficit

“…A well-known consequence of this conflicting information is the impairment in the ability to report the order of two stimuli, one applied to each hand, when hands are crossed (Heed & Azañón, 2014;Shore et al, 2002;Yamamoto & Kitazawa, 2001). In such instances, the order of two stimuli might be correctly computed, but it is inaccurately reported because of the incorrect localization of the stimuli in space (Badde, Heed, & Röder, 2016;Overvliet, Azañón, & Soto-Faraco, 2011;Roberts & Humphreys, 2008). This result has been interpreted as evidence that posture is taken into account automatically, even if it impairs task performance (Azañón, Camacho, & Soto-Faraco, 2010;Kitazawa, 2002;Yamamoto & Kitazawa, 2001).…”

“…The hand crossing effect has been suggested to result, amongst other models, from either an impairment of coordinate transformation (Yamamoto & Kitazawa, 2001) or a conflict in the integration of disparate spatial information (Badde et al, 2016;Badde, Röder, & Heed, 2015;Heed et al, 2015). Regardless of the interpretation of the origin of the effect, all these studies assume that the deficit indexes an automatic triggering of spatial transformations during tactile processing.…”

Reach Trajectories Characterize Tactile Localization for Sensorimotor Decision Making

“…However, reference frame transformations are abundant in sensorimotor processing and concurrent representation of information in different reference frames appears to be a common coding principle of the brain that usually does not lead to noticeable processing deficits (Andersen et al, 1993;Snyder, 2000;Pouget et al, 2002;Schlack et al, 2005;Pesaran et al, 2006;Chen et al, 2013;Makin et al, 2013). An alternative explanation of crossing effects is, therefore, that tactile localization comprises two distinct stages (Badde et al, 2014b(Badde et al, , 2015aHeed et al, 2015): (1) touch location is remapped from the anatomical into an external reference frame and (2) information from the two reference frames is integrated to derive an optimal touch location estimate. In this framework, coordinate transformation is fast and efficient for all postures and performance impairments in crossed postures are due to the integration of conflicting information available in different reference frames.…”

Gaze-centered coding of proprioceptive reach targets after effector movement: Testing the impact of online information, time of movement, and target distance

“…This demonstrates that participants, on average, used a gaze-centered reference frame for reaching to a proprioceptive target when they moved the hand that felt the target before the reach. This is likely caused by changes in the weighting of multiple spatial reference frames that are used in parallel ([19]; [8]) and are flexibly adapted to the sensory ([20]), motor ([21]; [10]; [19]), and cognitive context ([22]). In particular, our results indicate that the effector movement increased the weighting of a gaze-centered target representation.…”

“…However, this seems to be more variable depending on various factors (for a review see [7]), e.g. task demands ([8]) or effector movement ([9]; [10]; [11]).…”