Methodological Approach III
Creators: name: Veling, Harm
name: Tjepkema, Wim
name: Holland, Rob
Publisher: name: OSF Registries
Year: 2016

description: Participants
This study will be comprised of 25 participants (based on previous work in this domain[1,2]). We obtained an effect size of d = .77 of cue-approach training on choices for go items versus no-go items using similar stimulus materials in a previous study in our lab. The sample size (25) is more than sufficient to detect an effect of the training on choices for go versus no-go items using a one-sample t-test according to a power analysis[3]. However, we will use a repeated-measures logistic regression as our main analysis instead of a t-test in line with previous work. Recruitment will take place via the Radboud Research Participation System. Exclusion criteria are that participants should have no food restrictions/allergies, and have not participated in similar studies. Participants who bid less than €0.25 on auction items over 40 times will be excluded. Participants are asked not to consume any food items for at least three hours before the experiment commences. Sessions will last approximately one hour in total and will be conducted for either a €10 reimbursement or course credits.

Procedure and Measures
 Auction I and Item Ordering. In the study, participants are shown to a pantry where fruits and vegetables are stalled, receive €2, and are asked to give their informed consent. Then, they will practice and bid on 30 fruit and 30 vegetable items (one can be bought later) in a random-ordered Becker-DeGroot-Marschak auction (which measures their Willingness To Pay: WTP, indicating subjective value[4,5]) using a slider that ranges from €0 to €2. After this phase, all items are separated per category (fruit/vegetable) and are ordered from high (5-12) to low (19-26) value. 
 Cue-Avoidance Training. Then, participants receive cue-avoidance training toward 8 high-value (4 fruit, 4 vegetable) and 8 low-value (4 fruit, 4 vegetable) items. Item presentation (1 second) will be randomized within 8 blocks of 60 trials (~25% are cued items), including random jitter of 1.5 to 2.5 seconds between trials. Cue-presentation is delayed using a staircase procedure. In the task, participants have to continually press a keyboard button, and are instructed to release it when they hear the cue. This will be framed in terms of them ‘mimicking a natural reflex of humans to avoid rotten food’, where the cue signifies that a food item is rotten.
 Binary-Choice Task. Next, there will be a food-choice task in which participants get 1.5 seconds to choose between two same-category (fruit/vegetable), same-value items: one trained versus one untrained, for real consumption (32 unique pairs, presented four times across four blocks, with ~50% filler pairs, and random jitter of 1 to 2 seconds between trials). It is important to note here that participants will be extensively instructed that none of the foods will be rotten, as only fresh versions of them will be handed out after the experiment.
 Memory Recall Task and Auction II. Afterwards, participants will perform a memory recall task in which they are asked to indicate for all 60 food items whether they were paired with the cue or not. This is followed by a repetition of the first auction. 
 Questions. The experiment concludes with questions that measure the extent to which participants viewed the cued response they performed as being avoidant and approaching, followed by an open-ended question that asks them to indicate what they thought it was that the cue represented during the training.

Materials
 PsychoPy. Study 3 will be entirely programmed and conducted using PsychoPy[6]. The scripts and stimuli that will be used are included in this pre-registration. It is important to note here that, although a detailed description of the procedure is given above, the script is always leading. 
 Fruits and Vegetables. In total, 30 fruit and 30 vegetable (fresh) stimuli will be used in this study. These are all photographed in front of a black background, featuring the respective food item in its unaltered form, with a slice or piece of it next to it. All pictures have a resolution of 3008x2000 pixels and are matched in height and width. 

Analyses
To test whether the training has an effect on food choice, first a repeated-measures logistic regression analysis will be performed on choices for go versus no-go stimuli. Next, we will also explore whether the effects will differ for high and low value items and for fruits and vegetables. To test the effects on WTP, a 2 (time: pre/post) x 2 (item value: high/low) x 2 (condition: trained/untrained) repeated-measures ANOVA will be performed.