Fig. 2: Experimental design.
A On Day 1, participants rated each of 40 common consumer items and snack foods on their subjective drug relatedness and general desirability, among other dimensions. For each participant, these ratings were used to sub-select a 12-item choice set that (1) provided maximal spread in drug relatedness (that was of main interest here), while (2) de-coupling this dimension from general desirability thus minimizing the possibility of a systematic bias in the desirability of the items chosen as drug-related or nondrug-related (see Supplementary Information for details on selection of the initial 40-item fixed set and the choice set personalization procedure). The final selected choice sets only partly overlapped across participants, revealing a high degree of subjectivity in drug relatedness judgements (Fig. S1). B Following screening and choice set selection on Day 1, participants completed two task sessions, one after taking their daily methadone dose and the other ~24 h since the last dose of methadone (Days 2 and 3, randomized crossover order). Each task session was composed of 4 blocks. Each block was composed of 101 trials. Trials were randomly presented and consisted of 48 willingness-to-pay bid trials for each of the 12 items in the personalized choice set presented in 4 different quantities (depicted in blue), 48 desire rating trials for each of the same 12 items × 4 quantities (gray), 3 mood rating trials for each of happiness, stress, and boredom (teal), and 2 craving rating trials for each of heroin and methadone (red). For purposes of analysis, the three mood state ratings were averaged for each block into a composite negative mood measure and the two craving ratings were averaged into a composite opioid craving measure. To incentivize participants to provide their “true” momentary value (i.e., bid) for each item and to report only on their current subjective experience in each block, the task was structured such that it could end with a fixed (2%) probability after each block in a session, ending regardless after the 4th block. At the end of the session, one bid trial from the last completed block was randomly selected and played out to determine a participant’s bonus.
