Figure 1.
Hypothetical mechanisms by which predictability of forthcoming events modulates the decision-making process. a, Left panels illustrate the progressive drifts of decision variables toward their respective decision threshold. They also correspond to the activity predicted by the decision model for neural populations accumulating sensory evidence. A decision is made when a decision variable equates its threshold. Right panels illustrate how the reciprobit analysis of RT distributions reveals distinct regulatory mechanisms of the decision process. Threshold modulation hypothesis: Reciprobit lines swivel toward lower RT when predictability increases (top right panel), reflecting the lowering of the decision threshold (top left panel). Gain control hypothesis: Reciprobit lines shift toward lower RT when predictability increases (bottom right panel), reflecting the faster rise of the decision variable toward the decision threshold (bottom left panel). b, Task design. Participants had to identify a target shape out of three shapes by pressing a response button (red stars, ISI = 1.35 ± 0.76 s SD). Unbeknownst to the subjects, the next shape could be predicted on the basis of recent history. In first-order sequences, only the last trial had a predictive value on the next shape, whereas in second-order sequences, both the last and the penultimate trials had a predictive value on the next shape. c, Example of a set of transition rules from a first-order sequence. Arrows represent transitions from one shape to the next one and transition probabilities are indicated nearby each arrow.