Do small numbers pull young children's movements to the left?
Preschoolers who had not yet learned formal maths veered further left and moved more efficiently after seeing a small number of dots, suggesting the left-to-right number line exists before schooling.
Source
Kicking the mental number line: a kinematic investigation of numerical processing in childhood
Study at a glance
- Design
- Human experiment — Within-subject kinematic experiment: each child made identical finger 'kicks' toward a goal after a baseline picture or after 2-dot or 8-dot arrays (5 dots = no-go), with movements recorded by 3-D motion capture; preschool and school-age subgroups compared
- N
- N=21 · 21 right-handed children from preschool to late primary-school age, split for exploratory comparison into a small preschool group without formal maths teaching and a larger school-age group
- Population
- Italian preschool and primary-school children
- Outcome
- Finger trajectory kinematics, especially maximum leftward deviation, maximum trajectory height and peak velocity, compared across stimulus conditions and age groups
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What they did
Children wore a tiny soccer shoe on their right index finger and flicked a small ball toward a goal after each picture on a screen. The picture was either a drawing of a goal (baseline), two dots, or eight dots; five dots meant 'do not kick', which forced the children to actually process how many dots they saw. Because the kick was the same in every trial, any change in the finger's path could be attributed to the number seen. A 3-D motion-capture system tracked the finger, and preschoolers without formal maths teaching were compared with school-age children.
What they found
Preschoolers' kicks deviated further to the left after seeing two dots than after the baseline picture, fitting the idea that small numbers are mentally placed on the left. Preschoolers also made lower, more efficient trajectories after two dots, whereas eight dots did not differ from two dots on these measures. School-age children showed no reliable number effects on their trajectories, and within that group maths ability did not moderate the results. Across both groups, peak velocity was slightly lower after two dots than at baseline.
The limits
What it doesn't show
The sample was very small with a gender imbalance, and the preschool subgroup was only a handful of children, so the age comparison is exploratory. The baseline was a picture of a goal rather than a matched non-numerical array, and the dot arrays were not controlled for total area, so the effects might reflect visual properties that go along with numerosity rather than number itself. The study was not designed to tell whether small sets are handled by subitizing or by the approximate number system, and maths ability could only be measured in the older children. Some models fitted the data poorly and explained little variance, so modest effects should be generalised cautiously.
Key terms
- Mental number line
- The idea that people represent numbers along a spatial line, in Western cultures with small numbers on the left and large numbers on the right.
- SNARC effect
- Spatial-Numerical Association of Response Codes: faster left-side responses to small numbers and faster right-side responses to large numbers.
- Kinematics
- The detailed measurement of how a movement unfolds, such as its path, height, speed and timing, rather than just whether or how fast it is completed.
- Non-symbolic numerosity
- Quantity shown as a set of items, such as dots, rather than as a written digit or number word.
- No-go trial
- A trial where the participant must withhold the response, used here to make sure children actually processed the number of dots before moving.
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Quiz yourself
What did children do after each picture appeared?
Common questions
Why use a finger 'kick' instead of a grasp?
Grasping is tied to everyday experience that small objects need a small grip, which could create number effects through learned habits. A novel kick movement reduces that confound and is less affected by motor development.
Why do the results matter for theories of number?
If children who cannot yet count or calculate already show a leftward bias for small quantities, the spatial mapping of number may be an early foundation rather than something learned only through reading, writing and school maths.
Why might older children not show the effect?
The authors suggest that experience with symbolic digits and cultural conventions may reshape or mask the early non-symbolic mapping, which would also fit the mixed results with dot arrays in adults.
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