Right-hand preference facilitated by rightward turning biases during infancy

Area of Science:

• Developmental neuroscience
• Human motor development
• Infant reflexes

Background:

• Early human asymmetry, specifically a rightward turning bias, is observed in infants.
• This turning bias is hypothesized to be a precursor to established handedness.
• The Asymmetric Tonic Neck Reflex (ATNR) influences arm position during head turns.

Purpose of the Study:

• To investigate the coordinated influence of head-turning biases and the ATNR on the development of handedness.
• To measure reflex behavior during preferred versus non-preferred head-turning directions in infants.

Main Methods:

• Twenty infants were filmed during spontaneous movements.
• A factorial design was employed, varying head turn direction (left vs. right), volition (voluntary vs. passive), and angle (30° vs. 70°).
• The incidence, strength, and duration of the ATNR were systematically measured.

Main Results:

• The ATNR was least prevalent (in incidence, strength, and duration) when infants turned their heads towards their preferred side.
• For infants with a rightward preference, the occurrence of ATNR during rightward head turns was not statistically significant.
• This suggests minimal ATNR interference when orienting towards the right.

Conclusions:

• Head-turning biases and the ATNR interact to potentially promote handedness.
• Turning towards a preferred side minimizes ATNR intrusion on limb positioning.
• This mechanism may facilitate the development and establishment of right-handedness in infants.