Upon arrival at the laboratory, participants were endowed with $3 and
told that they would take part in an auction (Figure 1A). The auction procedure
followed the procedure of a Becker-Degroot-Marschak (BDM) auction 20. Single pictures of food items
appeared on the screen one at a time and participants placed their bid for each
individual item by selecting a value on a visual analog scale at the bottom of
the screen using a mouse. Participants were explicitly told that their best
strategy for the auction was to bid exactly what the item was worth to them to
buy from the experimenter at the end of the session. At the end of the session
a single trial was selected at random and played out such that the computer
generated a counter bid, which was a random number between 0 and 3 in 25 cent
increments. This number was compared to the participant’s bid on the randomly
selected trial and if the computer bid was higher than the participant’s, the
participant could not buy that item. If, however, the computer bid was lower
than the participant’s, then the latter was offered that item at the computer’s
bid lower price. This auction provided us a measure of willingness-to-pay (WTP)
for all 60 food items per participant. We used WTP to rank order the foods for
each participant from most preferred (highest WTP) to least preferred (lowest
WTP, Figure 2A). Items were split into high-value and low-value items. Items
were then placed into one of two training conditions; Go items required a
button press during training and NoGo items required no response from the
participant in adaptations of the cue-approach task 3. Item assignment to Go and NoGo
conditions based on their rank order was counterbalanced across participants.

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