In every trial, they view one of the study stimuli (3000 ms, choice period) and subsequently indicate with a button press (1500 ms, button press period) whether they want to eat a portion of the snack or not. During the button press period the words “yes” and “no” are shown left/right (randomized) on the screen. After indicating their choice, a yellow box appears around the yes or no. Participants are instructed to make their choice already during the period that the image was shown. To ensure that choices are made in direct response to the food pictures, the button press period was so short that it only allows them to locate whether they have to push the left or right button. The choice trials are interspersed with a random interval (between 2000 and 5000 ms). At the beginning, halfway (after 50 trials) and at the end an additional baseline period of 30 s is included in the task (fixation cross).
The visual stimuli consist of 100 pictures of regularly available snack foods on plates with a grey background: 50 high energy (HE) foods (energy content in kcal/100gram: M = 419, SD = 103) and 50 low energy (LE) foods (M = 56, SD = 37). Examples of HE snacks were crisps, cookies, cakes and candies. Examples of LE snacks were grapes, apples, bananas and mixed snack salads. The standardized image set can be downloaded from: http://nutritionalneuroscience.isi.uu.nl/index.php/32
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Experimental conditions are the subsets of an experiment that define the relevant experimental manipulation.
In the Cognitive Atlas, we define a contrast as any function over experimental conditions. The simplest contrast is the indicator value for a specific condition; more complex contrasts include linear or nonlinear functions of the indicator across different experimental conditions.
An indicator is a specific quantitative or qualitative variable that is recorded for analysis. These may include behavioral variables (such as response time, accuracy, or other measures of performance) or physiological variables (including genetics, psychophysiology, or brain imaging data).
van der Laan LN, de Ridder DT, Viergever MA, Smeets PA
Frontiers in neuroscience (Front Neurosci)
Citation added by Lvan der Laan about two years ago