A mental number line in human newborns

Area of Science:

• Cognitive Neuroscience
• Developmental Psychology
• Comparative Psychology

Background:

• Humans typically map smaller numbers to the left and larger numbers to the right on a mental number line.
• Spatial-numerical association (SNA) is observed in animals and infants, but its origin (innate vs. learned) is debated.

Purpose of the Study:

• To investigate whether spatial-numerical association (SNA) is present at birth in human neonates.
• To determine if SNA is based on the absolute or relative magnitude of numerousness.

Main Methods:

• Experiment 1: Tested 55-hour-old newborns' spontaneous association of numbers (4, 12, 36) with spatial locations after habituation.
• Experiment 2: Assessed if SNA depends on relative numerousness by varying the comparison number.
• Controlled for continuous physical variables to ensure effects were specific to discrete magnitudes.

Main Results:

• Newborns spontaneously associated smaller numbers (4) with the left and larger numbers (36) with the right, demonstrating SNA at birth.
• SNA in neonates was relative: the same number (12) was associated with the left when preceded by a larger number (36) and the right when preceded by a smaller number (4).
• The observed effects were specific to discrete numerical magnitudes, not continuous physical variables.

Conclusions:

• Spatial-numerical association in humans originates from pre-linguistic and biological brain precursors.
• Neonatal SNA is relative, not absolute, suggesting an innate, evolutionarily conserved mechanism for number representation.