Preliminary Analysis
All following analyses were completed by fitting mixed models for repeated measures using SAS Proc Mixed. All
models were specified with a random intercept, which is equivalent to a Repeated Measure ANOVA. Denominator degrees of freedom for within-subject variables were computed as number of observations—number of participants—number of predictors. First we evaluated whether missing eye-tracking data systematically biased our statistical analyses. To evaluate the percentage of time during which participants gazed at the screen, we computed the ‘On-task Percentage’. On-task Percentage was measured by summing all time spent in fixations as well as time looking at the screen in between fixations and dividing by the scene duration. Across participants, the mean On-task Percentage ranged between 90.40 and 100.00 % (M = 98.57, SD = 2.19). For all subsequent analyses, trials with an On-task Percentage smaller than 50 % were considered missing (14 trials). Results from fitting a mixed model using SAS Proc Mixed with On-task Percentage as outcome and experimental condition (i.e., congruent vs. incongruent) as a fixed effect showed that the mean On task Percentage did not differ significantly between the congruent and incongruent condition, F(1, 1,357) = 0.04, p = .83. Likewise, no significant associations were found between the On-task Percentage and participant age or gender, either as a main effect or interaction effects with experimental condition, p[.08.