Numerical cognition
Do more colours make a crowd of dots look bigger?
Open access · cc by · source: Europe PMC
Arrays made of many different colours looked more numerous than one-colour arrays, while colour helped counting only when same-coloured items were grouped together.
Study at a glance
- Design
- Human experiment — Two within-subject psychophysics experiments manipulating colour variety (1, 4 or 8 colours), spatial arrangement (clustered vs random) and numerosity (13-41 dots).
- N
- N=60 · 30 undergraduates in Experiment 1 (estimation) and a new group of 30 in Experiment 2 (counting).
- Population
- Chinese university students aged 18-23 with normal colour vision.
- Outcome
- Experiment 1: estimation error (estimate minus true number) after a brief display; Experiment 2: counting response time and error rate.
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Key findings
In the estimation task, eight-colour arrays were judged more numerous than single-colour arrays (estimates up by roughly 0.77-4.12%), regardless of whether colours were clustered or mixed; four colours did not differ reliably from one colour. In the counting task, clustered colours made counting of the largest arrays faster (about 7.05% faster with eight colours) and more accurate, whereas randomly mixed colours slowed counting without changing accuracy. The authors interpret this as colour variety acting as a cue for quantity under distributed attention, and colour clusters helping to guide focused attention during counting.
Methodology
In Experiment 1, 30 students saw arrays of coloured circles for just 300 ms and said aloud how many there were; arrays had one, four or eight colours, arranged either in same-colour clusters or randomly mixed. In Experiment 2, a new group of 30 students counted similar arrays as quickly and accurately as possible, with the display staying on until they finished. Both experiments used five target quantities between 13 and 41 plus filler quantities to stop people guessing.
Limitations
Each experiment had only 30 students from one university, and the gender balance differed sharply between the two groups. The size of the estimation bias was small, and the study does not pin down where it starts (four colours had no reliable effect) or whether it reflects numerosity itself versus perceived density. The attention-based explanation is inferred from behaviour rather than measured directly, and the arrays were simple dots in fixed grid positions, so the effect may differ with overlapping or real-world objects.
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