Experiment Author: Leah Suissa-Rocheleau, McGill University
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This experiment is adapted from Treadway et al. 2009's EEfRT task for food rewards.
This task includes both choice and forced trial types. Choice trials require a participant to choose a trial for a chance to have the trials' winnings included in a random draw of 2 trials. 3 probabilities of the trial reward being included in this draw are used to inform participants' choices: low, medium, and high probability.
Easy trials are worth 1 portion of food, whereas hard trials are worth 2-5 portions of food, but require more presses (effort expenditure) relative to the time duration (12 seconds), whereas the easy trials last 4 seconds.
A particularity of our task is that trials are calibrated to each participant's ability.
Based on tasks adapted by Dr. Stephen Benning at UNLV and other papers by Treadway, it seemed like the participants' completion rates of hard trials were low, incurring a floor effect.
Based on a quick literature search and a pilot study, easy trials had sometimes been calibrated to 0.33 of the average presses made during the 3 calibration trials, and 0.90 for hard.
Forced trials include a burst of white noise in order to measure startle eyeblink reflex magnitude and post auricular reflex magnitude. Given that we study eating disorders, we are interested in examining whether effort expenditure for a food reward affects aversive (startle) vs appetitive responding at the physiological level.
Forced trials do not have a probability manipulation and participants were led to believe that all completed forced trials were also included in the draw of food rewards.
Additionally, we measure self-reported hunger and wanting before receipt of reward, and liking afterwards.
A final particularity of this experiment is that it includes a mood induction manipulation- we are interested to see the effects of mood on reward for food in populations with and without disordered eating behaviour. Thus, personalized scripts of neutral vs stressful events are recorded and played to the participant, based Drs. Sinha and Tuit's imagery script development procedure inspired by Lang (1979)'s theory of imagery induction.
Self-reported emotion is logged before and after the mood induction, using randomized likert scales and the affect grid (Russell et al, 1989) to include a more visual measure of emotion.