Numerical cognition
Can seeing a small number nudge your hand to the left?
Open access · cc by · source: Europe PMC
When people were free to flick a ball left or right after seeing a number, the small digit 2 made them choose the left goal more often than chance and also changed the timing of their movement.
Study at a glance
- Design
- Human experiment — Within-subject free-choice task: participants flicked a ball with a finger toward a left or right goal after arrows (forced direction) or numbers (free choice), with 3D motion tracking of the finger
- N
- N=19 · 19 right-handed university students, each completing 100 test trials
- Population
- Right-handed young adult university students in Padova, Italy
- Outcome
- Proportion of left kicks after small vs large numbers; movement kinematics (movement time, timing of maximum trajectory deviation, preparation and finalization phases) compared with arrow baselines
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Key findings
Small numbers led to more left kicks than large numbers, and digits produced more left kicks than dot arrays. Only the digit 2 pushed left-kick choices reliably above chance; the digit 8 and both dot arrays did not. Kinematically, left kicks after the digit 2 and right kicks after the digit 8 both showed a longer preparation phase and a shorter finalization phase than baseline, whereas the dot arrays did not change the movement at all.
Methodology
Nineteen right-handed students wore a tiny soccer shoe on their right index finger and flicked a small ball toward one of two goals, one on the left and one on the right. On most trials an arrow told them which way to kick; on the rest they saw a small or large number (the digit 2 or 8, or an array of 2 or 8 dots) and could kick either way. Motion cameras tracked the finger so the researchers could split each kick into a preparation phase and a finalization phase and compare them with arrow-cued kicks.
Limitations
With only 19 participants and just 10 trials per number type, the study has limited power, and the authors acknowledge the sample could be seen as too small. Large numbers did not produce a clear rightward choice bias, partly because the right index finger's anatomy made left kicks easier overall, so the classic left-small / right-large pattern was only half confirmed in choices. The finding applied to digits but not to dot arrays, so it does not show that non-symbolic quantity biases action in the same way. The task is novel, so it is untested how well these effects generalize to other actions.
How this study connects
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