Summary of pairs and their performance on the spontaneous stone passing task (Test 1a & 2a).

Note: Eight subjects were naïve to stone passing as they had not performed the role of ‘dropper’ before their test. Six of the pairs were likely to be related (subjects were caught together), and six were likely to be unrelated (caught at different sites, at different times). Criterion: 3 out of 4 stones passed in one block.
Summary of pairs and their performance on the spontaneous stone passing task (Test 1a & 2a).