Proportion of correct responses by monkeys for stimulus pairs over successive trials.

Proportion of correct responses by monkeys for stimulus pairs over successive trials. Shaded areas represent 99% credible intervals. Top Row. Performance on stimulus pairs that included F and/or G for distances 1 through 5. Performance on all such pairs exceeded chance levels, and performance on xG pairs consistently exceeded that of xF pairs. Despite rapidly climbing to nearly 89.0% accuracy, the pair FG dropped immediately to 69.6% accuracy at the start of Phase 2. Bottom Row. Performance on pairs composed of items A through E. Performance on adjacent pairs generally remained low during Phase 2, but improved somewhat in Phase 3. Additionally, the six novel pairs in Phase 3 showed enhanced performance, consistent with a symbolic distance effect