Non-human primates can flexibly learn serial sequences and reorder context-dependent object sequences
Fig 1
(A) Each trial presented six objects. Monkeys learned to touch five objects in a pre-determined order A-B-C-D-E and avoid a distractor object. A correct choice led to visual feedback (yellow halo) and incremented the slider position of a progress bar on top of the screen. Monkeys received fluid reward upon completion of the sequence. (B) Each sequence was presented in 15 separate trials on the same ‘context 1’. Then the context changed and the object position 2 (object B) and 4 (object D) swapped (red font). After 5–6 “context 1 – context 2” pairs subjects performed a delayed match-to-sample (DMTS) task for 120 trials. Then, sequence learning was performed again with approximately 3 new and approximately 3 repeat-sequence pairs from earlier in the session. Sequences were presented on rock- or sand- themed contexts. (C) Prop. of correct choices for each ordinal position in context 1 averaged across trials 12–15. Darker dashed line indicates forward-looking chance level, i.e., assuming subjects do not consider reselecting previously correct objects. Lighter dashed line is absolute chance levels (1/6). Error bars are 95% conf. int. (D) Avg. rate of completing the 5-object sequences. Symbols mark the first trial (±SE) at which participants completed a sequence on average in 80% of all trials, with this level of performance sustained for at least three consecutive subsequent trials. (E) Avg. completion rate for the top third of ‘good’ sequences with lowest error rate (<5.33 errors) and for the bottom third of ‘poorer’ performed sequences (>6.6 errors). Red and blue triangles represent the mean trials to reach completion (±95% CI) for good and poor blocks, respectively, considering only blocks that reached completion threshold. The data underlying this figure can be found in the S1 Data file.