Does the crossed-limb deficit affect the uncrossed portions of limbs?

Abstract

When locating touch we remap its location from skin-based to external coordinates as a function of body posture. While remapping is thought to occur whenever there is tactile input, research has focused on a special case, the crossed-hands deficit, where tactile localization is impaired when the limbs are crossed, as compared to uncrossed. To date, these studies have always stimulated portions of the limbs that are crossed, such as a finger of each hand. It is therefore unknown whether the deficit induced by arm crossing is specific to the crossed portion of the limb or affects the limb as a whole. In Experiments 1 and 2, we stimulated the shoulders and elbows and found that tactile localization, measured with temporal order judgments, was unaffected by crossing the forearms. In Experiment 3, a crossed-limbs deficit was observed for touches on a single skin location when that location was distal -but not proximal -to the crossing point of the arms. In Experiment 4, we found a similar crossed-limbs deficit irrespective of how far distally to the crossing point touch was applied.Together, these results demonstrate that crossing the limbs affects tactile perception only distal to the point of crossing. The process of remapping tactile events does not take into account the endpoint location of the limb, but an extremely precise metric description of the touch relative to the configuration of both arms.

The standard posture of the hand.

“…Each stimulus consisted of three square-wave pulses with 30-ms on-phases (single pulse) and two interleaved 30-ms off-phases, resulting in a 150-ms vibration with a frequency of 17 Hz. This stimulation is similar to that used in our previous work (Romano et al, 2017), and other experiments involving suprathreshold tactile stimulations (e.g., Azañón, Radulova, Haggard, & Longo, 2016;.…”

The Sensitive Period for Tactile Remapping Does Not Include Early Infancy

“…In Figure , we compared performance of LM in the two postures with that of 343 participants from 12 published studies (Azañón et al., ; Azañón, Mihaljevic, et al., ; Azañón, Radulova, et al., ; Azañón & Soto‐Faraco, ; Badde et al., , ; Ley et al., ; Nishikawa et al., ; Roberts & Humphreys, ; Schicke & Röder, ; Wada et al., ; Yamamoto & Kitazawa, ) and two unpublished studies tested in similar bimanual crossed‐hand TOJ paradigms. LM's performance in the crossed‐hands posture was in the top 2–3% of the population (with a percentile of 98 and 97, for probit slopes and accuracy, respectively).…”

“…Data were taken with permission from 12 published studies and 2 unpublished studies that tested similar bimanual TOJ paradigms with crossed and uncrossed arms (corresponding to 22 experiments). Published data (included in parentheses are the names of the experiments and conditions): first study (Yamamoto & Kitazawa, ; main TOJ task): n = 20; second study (Wada, Yamamoto, & Kitazawa, ; left‐ and right‐handed groups): n = 32; third study (Schicke & Röder, ; hands‐only condition): n = 10; fourth study (Azañón & Soto‐Faraco, ; Experiments 1 and 2 ‐ congruent conditions only): n = 39; fifth study (Roberts & Humphreys, ; Experiments 1 and 2): n = 18; sixth study (Ley et al., ; controls for patient HS in Experiment 1): n = 5; seventh study (Badde et al., ; Experiment 2‐TOJ single task): n = 17; eighth study (Badde et al., ; TOJ task): n = 19; ninth study (Azañón, Stenner, Cardini, & Haggard, ; Experiment 1‐continuous condition): n = 12; 10th study (Nishikawa, Shimo, Wada, Hattori, & Kitazawa, ; young and elderly groups, participants that were tested both in the crossed and uncrossed conditions only): n = 41; 11th study (Azañón, Radulova, Haggard, & Longo, ; Experiments 1 and 4‐finger conditions): n = 29, 12th study (Azañón, Mihaljevic, & Longo, ; Experiments 1 , 2, and 3 ‐ aligned conditions only): n = 48. The unpublished data correspond to data of 39 participants (from currently two unpublished studies from our laboratory) plus the 14 controls for LM in this study.…”

Biases in hand perception are driven by somatosensory computations, not a distorted hand model

“…25,26 Placing the fingers or upper limbs in unusual postures leads to less efficient tactile processing. [27][28][29][30][31][32][33][34] Going beyond these observations, our work is the first to quantitatively define and empirically verify the influence of a postural prior on the perception of the body in space.…”