Learning
Do we learn less about someone who always shows up with a friend?
Open access · cc by · source: Europe PMC
People learned less about whether a partner was trustworthy when that partner always appeared alongside someone else, mirroring the 'overshadowing' effect seen in classic animal conditioning.
Study at a glance
- Design
- Human experiment — Within-subject Trust Game learning phase in which face partners were shown alone or in a pair and were always cooperative or always non-cooperative; cooperation ratings before and after learning; Experiment 2 added mixed-gender pairs, Experiment 3 added a between-subjects instruction manipulation (pair decisions ambiguous vs explicitly joint).
- N
- Separate samples per experiment: 48 in Experiment 1, 48 recruited in Experiment 2 with 46 analysed after exclusions, and 96 in Experiment 3; no single pooled N is reported.
- Population
- UK-born adults recruited online via Prolific, half women
- Outcome
- Change in rated likelihood of cooperating with each partner (test minus baseline), comparing partners learned alone versus in pairs
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Key findings
In all three experiments, ratings shifted more for partners learned alone than for partners learned in a pair, both upward for cooperative partners and downward for uncooperative ones, which is the signature of overshadowing. The effect was large and was not changed by the partners' gender, by the participant's gender, or by whether participants were told pair members decided jointly, which argues against a reasoning explanation. At baseline, before any learning, participants were more willing to cooperate with women than with men, but this gender bias did not alter the overshadowing effect.
Methodology
Online participants played a repeated Trust Game: on each trial they saw a face (or a pair of faces) and chose whether to invest £1, which the partner could repay or keep. Some partners appeared alone and others always appeared in a fixed pair, and each partner was either always cooperative or always uncooperative; participants saw what the partner did even when they chose not to invest. Before and after this learning phase they rated how likely they were to cooperate with each individual face shown alone. Experiment 2 added mixed-gender pairs and Experiment 3 told half the participants that pair decisions were always made jointly.
Limitations
Participants received feedback about partners even on trials where they did not invest, which real life rarely provides, so learning may have been unusually accurate; the authors note that more realistic one-sided feedback might weaken the effect. Partners were photographs with fully scripted, perfectly consistent behaviour, so it is unclear how the effect holds with real, variable people. The absence of gender effects is a null result that does not rule out stereotypes mattering with more salient categories or harder tasks. The samples were UK-only online volunteers.
How this study connects
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