Methodological Approach II
Creators: name: Tjepkema, Wim
Publisher: name: OSF Registries
Year: 2016

description: Participants
The sample size will be 25 participants per sub-study, 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
In both sub-studies, 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. Then, participants receive motor movement training toward 8 high-value (4 fruit, 4 vegetable) and 8 low-value (4 fruit, 4 vegetable) items in response to an auditory cue. 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 first study, participants have to continually press a keyboard button, and are instructed to release it when they hear the cue. In the second study, participants will either do this reversed (identical to the original cue-approach paradigm), or will receive more detailed instructions on how to perceive their performed motor movements. 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). The experiment ends with a memory recall task, followed by a repetition of the first auction, after which participants are thanked, reimbursed and receive/buy their two pseudo-randomly selected fruits/vegetables. 

Materials
 PsychoPy. Study 2 will be entirely programmed and conducted using PsychoPy[6]. The scripts and stimuli that will be used in Study 2 are included in this pre-registration. It is important to note here that, although a detailed description of the procedure is given, the script is always leading. 
 Fruits and Vegetables. In total, 30 fruit and 30 vegetable stimuli will be used in Study 2. 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 respective type of 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.