Reach Trajectories Characterize Tactile Localization for Sensorimotor Decision Making

Abstract

Spatial target information for movement planning appears to be coded in a gaze-centered reference frame. In touch, however, location is initially coded with reference to the skin. Therefore, the tactile spatial location must be derived by integrating skin location and posture. It has been suggested that this recoding is impaired when the limb is placed in the opposite hemispace, for example, by limb crossing. Here, human participants reached toward visual and tactile targets located at uncrossed and crossed feet in a sensorimotor decision task. We characterized stimulus recoding by analyzing the timing and spatial profile of hand reaches. For tactile targets at crossed feet, skin-based information implicates the incorrect side, and only recoded information points to the correct location. Participants initiated straight reaches and redirected the hand toward a target presented in midflight. Trajectories to visual targets were unaffected by foot crossing. In contrast, trajectories to tactile targets were redirected later with crossed than uncrossed feet. Reaches to crossed feet usually continued straight until they were directed toward the correct tactile target and were not biased toward the skin-based target location. Occasional, far deflections toward the incorrect target were most likely when this target was implicated by trial history. These results are inconsistent with the suggestion that spatial transformations in touch are impaired by limb crossing, but are consistent with tactile location being recoded rapidly and efficiently, followed by integration of skin-based and external information to specify the reach target. This process may be implemented in a bounded integrator framework.

Spatially modulated alpha-band activity does not mediate tactile remapping and fast overt orienting behavior

“…This finding replicates our observation in a free-viewing task of natural scenes (Ossandón et al, 2015). While a purely external effect of touch on saccades is in agreement with previous studies (Groh and Sparks, 1996;Blanke and Grüsser, 2001;Overvliet et al, 2011;Buchholz et al, 2012), both saccades and reaches towards tactile locations can exhibit trajectories that initially deviate towards the anatomical side of the tactile event (Groh and Sparks, 1996;Overvliet et al, 2011;Brandes and Heed, 2015). Note that, in those tasks, the tactile stimulus location was the movement goal.…”

“…However, one must bear in mind that our time estimates are averages across many trials, and that the stimulation only affected some saccades at 100 ms, becoming more consistent only at later time points. In a previous study, we compared when participants initiated a turn of a straight hand reach towards a visual or a tactile stimulus, presented in-flight (Brandes and Heed, 2015). Tactually evoked turns were only 20 ms slower after tactile stimulation to uncrossed limbs than to visual stimuli at identical locations, thus suggesting a very short estimate for the computation of an externalspatial location of touch.…”

“…Previous estimates of when external tactile information first guides behavior have been inconsistent, ranging from about 150 to 360 ms (Yamamoto and Kitazawa, 2001;Azañón and Soto-Faraco, 2008;Overvliet et al, 2011;Brandes and Heed, 2015). At 100 ms response time, externally directed saccade responses were considerably faster here, and conflict resulting from crossed limbs was resolved after 200 ms, consistent with our previous report about hand reach corrections to tactile stimuli (Brandes and Heed, 2015). The time from programming a saccade to its execution has been estimated to lie around 100 ms, based on countermanding and saccade inhibition tasks (Hanes and Carpenter, 1999;Reingold and Stampe, 1999).…”

“…Second, if alpha-band modulation played a causal role in tactile remapping, it should precede any externally oriented behavior in response to touch. Yet, whereas estimates for the time requirements of tactile remapping range from 150-300 ms (Yamamoto and Kitazawa, 2001;Azañón and Soto-Faraco, 2008;Overvliet et al, 2011;Brandes and Heed, 2015) alphaband modulation has been demonstrated in tasks that implement long delays of >1s between attentional cue and tactile stimulus, or between tactile stimulus and response. During these delays, alpha-band suppression often develops gradually and is strongest at the end (Buchholz et al, 2011(Buchholz et al, , 2013van Ede et al, 2011van Ede et al, , 2014Bauer et al, 2012;Schubert et al, 2015).…”

Task demands affect spatial reference frame weighting during tactile localization in sighted and congenitally blind adults

“…It has been suggested that a full random effects structure should be 321 used for significance testing in (G)LMM (Barr, Levy, Scheepers, & Tily, 2013). However, it has been shown 322 that conclusions about fixed effect predictors do not diverge between models with maximal and models 323 with parsimonious random effects structure(Bates, Kliegl, Vasishth, & Baayen, 2015), and it is common 324 practice to include the maximum possible number of random factors when a full structure does not 325 result in model convergence (e.g.,Bolker et al, 2009;Brandes & Heed, 2015). In the present study, 326 models reliably converged when we included random intercepts and slopes per participant for each main 327 effect, but not for interactions.…”