Can a low-cost eye-tracker assess the impact of a valent stimulus? A study replicating the visual backward masking paradigm

Capturing affective response to valent stimuli using eye-tracking is not only of interest to academic research, but also to commercial equipment developers (e.g., car dashboards). In order to investigate whether a low-cost eye-tracker can effectively detect participants’ physiological response to negatively valent stimuli, forty-four participants aged 19-24 (mean = 24.7, SD = 5.8) were recruited to complete the visual backward masking paradigm in a repeated-measures experimental design. Saccadic duration and pupil sizes were recorded using a lower-end 60-hz tracker. Data was analysed using a mix of parametric and non-parametric tests. Our results suggest that valence in the form of fearful vs neutral faces has a significant main effect on both saccadic duration [V = 931, p < 0.001, d = 0.96] and pupil size [t(43) = 29.81, p < 0.001, d = 3.91)]. Our findings were further supported by Bayes Factor analysis, which showed that saccadic duration data was 24 times more likely to occur, and pupil size measurement data was 89 times more likely, under the alternative hypothesis, showing that differences in valence had a main effect. The combined evidence produced by our Bayesian analysis, the large effect sizes of our frequentist analysis, and the significant effect on two separate measurements lead us to suggest that, under the right conditions, low-cost eye trackers can successfully detect changes in saccadic duration and pupil sizes as a result of physiological responses to threat-relevant visual stimuli