The lower body becomes mapped as a sensorimotor reaching space during the first year

• In Event: Poster Session 05
  In Poster Session: PS 05 Topic - Perceptual, Sensory, Motor

Abstract

Individuals routinely localize and reach to targets positioned on the skin. This ability has great adaptive value. It enables individuals to feed themselves, remove aversive stimuli, and may also advance a sense of self (Amsterdam, 1972). Little is known, however, about the origins of this self-localization ability. Previously, researchers found that localizing and reaching to targets on the face develops gradually across the first year (Chinn, et al., 2020). Here we longitudinally examined how this ability develops across the lower body, beginning near four months.

Method. Infants were placed on their backs on folded blankets and were moved to a reclined seat if they became fussy or rolled over during testing trials. During each session, we adhered small vibrating discs, one at a time on individual trials in random order to nine abdomen/leg/foot locations. Locations included the left/center/right abdomen, left/right thigh, left/right shin, and left/right foot (See Figure 1). Infants (N=18, 10 males) participated in approximately biweekly sessions from four months until successful localization of all discs or up to 15-months. Due to the COVID-19 pandemic, nine infants did not complete the study, and we used generalized linear mixed effects models (GLMM) analyses that could adjust for missing data.

Videos were coded for target location (inter-rater reliability: ƙ=0.99), vibrating disc contact (no contact/removal vs. contact/removal; inter-rater reliability: ƙ=0.89), and contact effector/strategy (e.g., hand, arm, shook buzzer off, leg, etc.; inter-rater reliability: ƙ=0.84).

Results
For 34 trials, infants rolled over before the trial could be completed. For the remaining trials, infants contacted and/or removed the target (hereafter termed localization) on 355 out of 630 trials. Infants were similarly likely to localize left and right lateralized targets (154/276 left; 157/282 right), and most localizations (274/355) were made with the hand. A number of other target removal or reaching strategies were observed, with the most common being contacting the target with the lower arm (N=37), contacting with the leg (N=28), contacting with the foot (N=18), or shaking the target off (N=12). Success at localizing the targets significantly increased with increasing age (Wald χ21=41.01, p<.001; See Figure 2).

Conclusions. We found that infants’ functional maps of the lower body developed gradually across the first year. Infants became more likely to contact and/or remove targets with increasing age. As with previous work on face and arm body-reaching (Chinn et al., 2020; Leed, Chinn, & Lockman, 2019), the most common tactile localization strategy was to use the hand. However, we found that infants use alternative strategies for lower body targets approximately 22.8% of the time. Data collection will continue when safe, and we will further analyze reaching strategies, ipsilateral versus contralateral reaching, and the hypothesis that localization ability progresses in a cephalocaudal direction with increasing age. Mechanisms for the emergence of lower body maps based on self-touch experience will also be considered in future work.

Authors

• Lisa K. Chinn, University of Houston
  Non-Presenting Author

• Katarina S. Patton, Tulane University
  Non-Presenting Author

• Caroline Mayberry, Tulane University
  Non-Presenting Author

• Claire Elise Dame, Tulane University
  Non-Presenting Author

• Jeffrey J Lockman, Tulane University
  Presenting Author