Within each condition, there was a within-group variable of model age (adult or child), with each
model demonstrating one of two different methods for reward retrieval (arrow or rake, counterbalanced
and explained further below) sequentially (order of model demonstration was counterbalanced).
There were two between-participant variables: (a) demonstration efficacy shown through
completeness (three levels: complete, near-complete, or partial) and (b) demonstration efficiency
shown through irrelevant actions (two levels: present or absent). Table 1 summarizes the seven six
experimental conditions. There was an additional ‘‘no-demonstration” control condition that offered
no demonstration of any kind; here each model was paired only with a photograph of one of the
two tools