Figure 4.

Choices in variable- and fixed-reward conditions. (A) Extinction phase. Probabilities of the optimal choice were quantified before and during extinction-phase trials, which were introduced in the variable- and fixed-reward conditions. Means and standard errors are shown. Before the extinction phase, reward probabilities of variable- and fixed-reward conditions were identical: ^*p < 0.05; ^**p < 0.01 in a Mann–Whitney U-test. (Bi) Example of a conditional-probability calculation in repeated (a) and interleaved sequences (b). Depending on the action-outcome experience at trial t-1 for (a) and trial t-2 for (b), the conditional probability at trial t was analyzed. In these examples, the conditional probability of variable-reward-condition trial (Var.) was analyzed, based on the action-outcome experience in the last and the next-to-last trial with a variable-reward condition in (a) and (b), respectively. In (b), the experience in the interleaved trial t-1 with the fixed-reward condition was ignored. Action-outcome experiences had 4 types: optimal choice rewarded (Opt. rewarded); optimal choice not rewarded (Opt. not rewarded); non-optimal choice rewarded (Non-Opt. rewarded); non-optimal choice not rewarded (Non-opt. not rewarded). If the choices of variable- and fixed-reward conditions were independently learned, the conditional probabilities of repeated and interleaved sequences became the same. (ii,iii) Comparison of conditional probabilities in variable- (ii) and fixed-reward condition (iii). Conditional probabilities of making a choice to the optimal side of fixed-reward condition were compared between repeated (white bars) and interleaved sequences (black bars). Means and standard errors of probabilities are shown. Dotted line shows the average choice probability. White and black bars indicate significant differences under some action-outcome experiences, meaning that the interleaved trial interferingly affected the choices: ^**p < 0.01 in a Mann–Whitney U-test.