The Proprioceptive Origins of Infant Reaching

• In Event: The Role of Proprioception in the Development of Reaching and Knowledge About the Self

Abstract

In recent decades, the role of vision in the emergence of infant reaching has been downplayed. Infants can reach in the dark and control their arm trajectory by modulating the dynamic forces of the movement without using vision. Recently, it has even been suggested that at reach onset, infants calibrate their vision to their reaching movement and not the reverse as thought before. Thus, it appears that learning to reach in infancy depends greatly on the proprioceptive experience of the arm movements acquired during the weeks preceding the emergence of reaching.

Learning how to move our arms, knowing where to direct them in space, and knowing how far they can extend in our peripersonal space are all fundamental prerequisites to the formation of goal-directed actions and they rely heavily on proprioceptive information. Such movement prerequisites must be grounded in the self-generated movements that infants perform spontaneously from birth and in the absence of visual control. The aim of this study was to study these early arm movements to gain a better understanding of the proprioceptive origins of infant reaching.

Five newborns were followed weekly from the age of 3 weeks until they gained head control (between 10-13 weeks old). They were observed while alert and in supine for five 5-minute conditions (baseline, toys-in-view, sounding toy, mother speaking, & overhead mobile) to a total of 25 minutes. The kinematics of both arm movements were recorded continuously using a motion analysis system sampling at 120Hz. Two video cameras, synched with the motion tracker, recorded a view of the infant from above. The video recordings were used to detect all the hand touches the infants performed on their body or the supporting surface. These moments of touch were then reported on the kinematic time series to extract all individual movement trajectories each hand performed from one point of contact to the next.

Preliminary analyses revealed that infants performed hundreds of hand touches on the body and supporting surface per 5-minute time window, yielding to a large number of movement segments where the hands traveled from one point of contact to the next. Fifty percent of the time, the hands were in motion, in the air, and not in contact with the body or surface. Furthermore, contacts to the body/surface covered all the areas the infants’ hands could reach. Analyses of the movement kinematics revealed that hand trajectories in the air were extremely variable and covering a broad space area. Finally, analyses on the speed of hands at times of contact with the body or surface revealed differential responses. The face and shoulder areas were touched with lower speed than the body or surface.

These data indicate that during wake times, young infants are actively moving their arms, exploring their body and their peripersonal space. These self-generated movement experiences provide a wide range of proprioceptive feedback that can help infants calibrate their peripersonal space. This early experience is essential to the formation of goal-directed movements.

Author

• Daniela Corbetta, University of Tennessee - Knoxville
  Presenting Author