Figure 1. Object value learning and memory paradigm.

(A) Reward training: Monkeys first fixated centrally and after the instruction (fixation off) made a saccade to a 10°-15° peripheral target (or stayed at center if target shown centrally) and held gaze to receive low or high reward (bad and good objects, respectively). Paired reward was always the same for a given object in all trials (left). Passive viewing test: Monkeys kept central fixation while good and bad objects were shown randomly and sequentially in the neuron’s receptive field (RF) without reward (right). (B) Acute neural recordings were performed during passive viewing (blue block) to test value memory in objects previously trained with reward (black block) and during reward training of new objects (gray block) and previously trained objects (black block >10 days). Reward-based long-term memory was measured hours, days, weeks or months after last object-reward association, during which monkeys were still trained with many other objects (left). Different memory scales within individual neurons could be examined by using objects trained months ago in one block and objects trained days ago in another block. To test the effect of learning, a given neuron could be recorded using novel objects in one block and previously trained objects in another block (example recording session, right). (C) Fractals (>100) used for monkey B in value memory test. Fractals were simultaneously trained and tested in sets of 8 objects. See also Figures S1 and S2