Study title

United Kingdom

Individual

Aside from the variations noted below, the experiments proceeded as follows. Participants were recruited from the University of Warwick participation pool and were paid for their participation. To limit movement, participants used a chin rest placed approximately 70cm away from the screen. Monocular eye movements were recorded at 500Hz with an EyeLink 1000 Plus (SR Research, Osgoode, ON, Canada) eye-tracker. Fixations were identified by the eye-tracker software using velocity algorithms. Participants initially underwent a 13 point calibration and validation cycle of the eye-tracker, which was repeated throughout the experiments. Stimulus presentation was controlled by MATLAB using Psychtoolbox extensions. Trials were excluded if their reaction times were greater than 1.5 times the interquartile range above the mean reaction time across all trials within the experiment or less than 200ms. FoodUseable data was collected from 41 participants. Data was excluded for 4 additional subjects because of poor eye tracking data quality (as indicated by the proportion of time during trials where eye gaze was detected by the tracker being outside of the normal distribution across all participants). The stimuli were pictures of 50 different snack items. These were comprised of five types of snack: crisps, fruit candy, sweet carbonated drinks, health and sports drinks, and chocolate. This experiment was split into two parts. In the first, the participant rated the desirability of 50 snack items on a 1-9 scale. In the second, the 50 stimuli were paired to create 100 binary choice trials. Choice pairs were created such that the rating difference between the two items was 3 or less, and so that an individual snack item was not present in more than 5 trials. At the end of the experiment one trial was randomly selected and the subject was given the item they chose.PostersUseable data was collected from 53 participants. The experiment was displayed on a widescreen monitor (1920 x 1080 resolution, 60Hz refresh). Additional data was collected from 13 participants but 12 were excluded due to a programming error and one because their gaze location could be measured for less than 70% of the time across all trials. The stimuli were chosen from the International Affective Picture System. The pictures were all positive in affect (average ratings between 5=neutral and 7=mildly positive for both males and females) and had differences in value ratings of no more than 1.5 between male and female raters. After visual inspection, a further 7 images were removed for containing sexual images and 32 images were removed because they had a portrait aspect ratio. The 200 stimuli for each participant were randomly sampled without replacement from the 253 pictures that met these criteria.All participants completed binary choice and strength-of-preference tasks in a counterbalanced order. Here, we only analyse the binary choice data. Two landscape pictures (each 514 x 384px) were displayed side by side following a fixation cross. The response scale was presented horizontally centered, below the stimuli. For the binary choice task, two labels (``Option A'' and ``Option B'') were shown underneath the appropriate stimuli. The current choice was signified by a red, square marker (30 x 30px) above the label. The marker was initially centered equidistant between the two images. To respond, the participants had to press the left mouse button. Reaction times were measured from the start of the trial to the mouse click onset. A blank, black screen was displayed for 500ms between each trial. Finally, participants had to rate their overall liking for each picture on a Likert scale, vertically displayed to the left of each image. The eye-tracker was recalibrated at the beginning of each condition and then after every 25 trials.LotteryUseable data was collected from 54 participants. The data of an additional 5 subjects was excluded: 1 because they failed to complete the task within a reasonable time frame and withdrew, and 4 because of poor quality eye tracking data. The stimuli were gambles with three equally likely outcomes. Because the outcomes were equally likely, no probabilities or likelihoods were displayed during the trials themselves. For each trial, two gambles were presented, one on the top and one on the bottom of the screen. The three payouts of a single gamble were presented in horizontal alignment and were displayed as white text within a solid grey circle. This was done to reduce the discriminability of the numbers in peripheral vision, so that subjects had to directly fixate the number to determine its value. Each gamble consisted of three possible outcomes which were always one low value (10-30), one medium value (40-60), and one high value (70-90). The specific values were randomly drawn on each trial. The main task consisted of 100 trials. Trials were presented in a random order, with trials from the different conditions intermixed. Each trial began with a fixation cross displayed in the centre of the screen, and the trial only began once the subject was looking at the fixation cross. Trials were split into 3 different conditions: no change, low to high, and high to low. There were 34 trials in the no change condition, and 33 in each of the other two. Here, we only analyse the no change condition. The eye-tracker was recalibrated at the beginning of the main block and then after every 20 trials.CurrencyUsable data was collected from 46 participants from the California Institute of Technology participation pool. Additional data had been collected from 14 participants but four were excluded due to incomplete data (they ran over the experiment slot) and 10 because of poor eye tracking accuracy (their gaze location could be measured for less than 68% of the time averaged across all trials). The stimuli were two gambles with three equally likely outcomes, presented at the top and bottom of the screen. The three payouts of each option were presented side-by-side as white text within a solid grey circle. There were two within-subject conditions, counterbalanced for order. In the commensurate condition, there were 42 trials, in a third of trials all attributes were displayed in pounds, yen and ``Q'' respectively. In the incommensurate condition, on every trial, the three attributes of each option were presented in the three difference currencies. Here, we only analyse the commensurate condition. Participants were told the exchange rates for pounds, yen and Q to dollars. Here we analysed the equivalent dollar values. The eye-tracker was calibrated at the beginning and every 21 trials. Participants pressed the up key if they preferred the top lottery, and the down key if they preferred the bottom lottery. Areas of interested were defined horizontal distance of 320 pixels, and a vertical distance of 340 pixels apart on the screen.