Numerical cognition
Can the link between numbers and space be split between two people?
Open access · cc by · source: Europe PMC
People judged numbers slightly faster when a human partner's arrow rule matched the small-left, large-right number line, but a computer partner produced no such effect.
Study at a glance
- Design
- Human experiment — Social go/no-go task: the participant responded only to digits smaller or larger than 5 on a single central key, while a partner (a confederate or a computer) was assigned left- or right-facing arrows; rule pairings were congruent or incongruent with the mental number line; partner type varied between subjects
- N
- N=48 · 48 University of Bologna students, 24 paired with a human confederate and 24 paired with a computer
- Population
- Italian university students with normal or corrected vision, naive to the purpose of the study
- Outcome
- Reaction time to go trials for digits under rule pairings that were congruent (small/left, large/right) versus incongruent (small/right, large/left) with typical spatial-numerical associations
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Key findings
With a human partner, participants responded about 11 ms faster in congruent than incongruent blocks, a small but reliable effect supported moderately by a Bayesian analysis. With a computer partner there was no congruency benefit (a non-significant difference of about -5 ms in the opposite direction). The difference between the two partner conditions was significant, while overall speed did not differ between conditions or between small and large numbers.
Methodology
Each participant sat facing a partner across a table and pressed one central key only for digits smaller (or larger) than 5, while the partner was supposedly responding to left- or right-pointing arrows on another laptop. Across four blocks the pairing of the participant's number rule with the partner's arrow rule was either congruent with the mental number line (small with left, large with right) or incongruent. For half the participants the partner was a same-sex confederate; for the other half the partner was simply a computer. Because the participant's own task had no spatial component at all, any congruency effect had to come from representing the partner's rule.
Limitations
The human-partner effect is small (Cohen's d of 0.27) and comes from only 24 people per condition, so it needs replication; the authors note it was smaller than in earlier single-person versions. Partner type was manipulated between subjects rather than within, and there was no manipulation check of whether participants believed the partner was acting or saw the computer as an agent. The confederate never actually pressed a key, so the study cannot say which features of a real co-actor (visibility, humanness, believed agency) are critical. Error rates were too low to analyse, so conclusions rest on reaction times alone.
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