# A pupillary index of susceptibility to decision biases The demonstration that human decision making can systematically violate the laws of rationality has had wide ranging impact on the fields of economics and psychology. However, the cognitive processes that give rise to irrational biases are still poorly understood. In this study, we use a pupillary index to adjudicate between two predominant existing hypotheses – the hypothesis that biases result from fast effortless processing and the hypothesis that biases result from more extensive integration. While effortless processing is associated with smaller pupillary responses, more extensive integration has been shown to be associated with larger pupillary responses. Thus, we tested the relationship between pupil responses and choice behavior on six different foundational decision-making tasks classically used to demonstrate irrational biases. Participants’ decisions demonstrated the systematic biases reported in the literature, and their pupillary measurements satisfied pre-specified quality checks. Planned analyses, however, retuned inconclusive results. Further exploratory examination of the data revealed an association of high pupillary responses with biased decisions. We conclude that the findings are inconsistent with an effort-based explanation of susceptibility to biases, and provide preliminary support for the hypothesis that biases arise from gradual information integration, potentially due to low levels of neural gain. ## File Structure ``` +-- experiment_code/ <-- Contains all code to run the experiment. See the README in the folder for more information. +-- analysis_code/ | +-- AnalysisAllMain.m <-- Main pre-registered analysis | +-- AnalysisAllRT.m <-- Supplementary analysis using the reaction times in the oddball task | +-- AnalysisAllOddball.m <-- Supplementary analysis using the pupillary reasponses in the oddball task | +-- Analysis.m <-- Analyze one participant's data | +-- clearBlinksAndArtifacts.m <-- Function to identify artifacts and interpolat | +-- EyeTracking.m <-- Processes eye-tracking data and outputs the processed eye-tracking data files | +-- OddballQCs.m <-- Run QCs on Oddball task | +-- seeExcluded.m <-- Finds number of subjects per task (for each analysis) with missing data | +-- BayesianModeling.R <-- Runs the Bayesian model using RStan | +-- BayesianModel.STAN <-- Specifies the Bayesian model | +-- BayesianModelingFigure.R. <-- Creates Figure 4a | +-- LMMs.R <-- Runs the mixed effects linear models | +-- data/ | | +-- results_phas_task.mat <-- Results from running AnalysisAllMain.m | | +-- results_phas_task.csv | | +-- results_rt_oddball.mat <-- Results from running AnalysisAllRT.m | | +-- results_rt_oddball.csv | | +-- results_phas_oddball.mat <-- Results from running AnalysisAllOddball.m | | +-- results_phas_oddball.csv | | +-- oddball_data.mat <-- Results from running OddballQC.m | | +-- modeling_pupil_all.RData <-- Results of modelling in R | +-- plots/ | | +-- phas_task.fig <-- Terciles for each task, corresponding to the analysis in AnalysisAllMain.m | | +-- rt_oddball.fig <-- Terciles for each task, corresponding to the analysis in AnalysisAllRT.m | | +-- phas_oddball.fig <-- Terciles for each task, corresponding to the analysis in AnalysisAllOddball.m | | +-- timecourse_tasks.fig <-- Time course of pupil response in the decision making tasks | | +-- timecourse_oddball.fig. <-- Time course of pupil response in the oddball task +-- data/ | +-- SubjectLog.xlsx <-- Subject log | +-- main_data/ <-- Data for all subjects used in the main analysis | | +-- Subject XXX | | | +-- EyeTracking.mat <-- Processed eye-tracking data | | | +-- SXXX_YYYYMMDD_HHMMSS Samples.txt <-- Raw eye-tracking data | | | +-- SXXX_YYYYMMDD_HHMMSS.mat <-- Behavioral data | | +-- ... | +-- excluded_data/ <-- Excluded data, contains raw data (when available), in similar subject subdirectories as the main data folder | | +-- ... | +-- broken_data/ <-- Raw data for two (included) subjects whose data was saved in two parts; the combined data files are also in the main data folder | | +-- ... ``` ## Requirements Analysis code is written using both Matlab and R, with RStan. The experiment code requires both Matlab and Psychtoolbox.