Figure 1
Full face stimuli with different pupil sizes were presented in the first block of trials (a). Example of eye regions before and after luminance/contrast equalization (b). The eyes’ pixel values were equalized for luminance and contrast (c) such that eyes with large pupils got brighter with less contrast while small pupils got darker with more contrast (b). Slits of the eye region of the faces were shown in the second and third block of trials (d). Schematic overview of the procedure of luminance equalization for the video stimuli in experiment 2 (e). Snapshots of a happy, European, female face with dilated pupils (left) and an angry, Japanese, male face with constricted pupils (right) in which the brightness of the pupil was corrected to ensure equal luminance across video frames as a function of pupil size (f). These images were adapted with permission from Kret et al. (2015).
Table 1
Confusion matrix with the average and standard error of percentages of the observed emotional expressions in experiment 1 across participants (subjective; columns) per shown emotional expression (objective ground truth; rows).
| Confusion matrix % | Happy | Neutral | Angry | Sad |
|---|---|---|---|---|
| Happy | 97% ± 1 | 1% ± 0 | 1% ± 1 | 1% ± 1 |
| Neutral | 2% ± 1 | 98% ± 1 | 0% ± 0 | 0% ± 1 |
| Angry | 0% ± 0 | 4% ± 1 | 94% ± 1 | 2% ± 1 |
| Sad | 0% ± 0 | 4% ± 2 | 4% ± 2 | 92% ± 2 |
Figure 2
The left plot shows the average change in pupil size across observers as a function of time from slit onset (solid lines) per observed pupil-size condition (small pupil: blue; original pupil: red; large pupil: black) in experiment 1. The displayed eye regions in the slits were not equalized in luminance and contrast. The dotted lines around the solid lines indicate standard errors of the mean. The right plot shows the average and standard error of the change in pupil size across observers, after averaging between 1 and 3 seconds from slit onset, per observed pupil-size condition (small: S; original: O; large: L; n.s.: not significant).
Table 2
Means, confidence intervals, and post-hoc t-test comparisons across pupil size conditions per block in experiment 1 (Blo.).
| Blo. | Compared conditions | Mean difference | Confidence interval | t-value | p-value | Cohen’s D | BF | |
|---|---|---|---|---|---|---|---|---|
| 1 | Small | Original | 0.01 | –0.08/0.10 | 0.22 | 0.823 | 0.233 | 0.145 |
| Original | Large | 0.02 | –0.08/0.09 | 0.13 | 0.894 | 0.235 | 0.142 | |
| Small | Large | 0.01 | –0.08/0.11 | 0.33 | 0.745 | 0.188 | 0.149 | |
| 2 | Small | Original | –0.10 | –0.17/–0.01 | 2.35 | 0.022 | 0.438 | 1.778 |
| Original | Large | 0.06 | –0.02/0.15 | 1.46 | 0.149 | 0.132 | 0.386 | |
| Small | Large | –0.03 | –0.13/0.06 | 0.70 | 0.490 | 0.195 | 0.178 | |
| 3 | Small | Original | 0.02 | –0.02/0.06 | 0.96 | 0.339 | 0.068 | 0.220 |
| Original | Large | –0.02 | –0.06/0.02 | 1.08 | 0.287 | 0.079 | 0.244 | |
| Small | Large | –0.00 | –0.04/0.03 | 0.15 | 0.882 | 0.010 | 0.143 | |
Figure 3
The left plots shows the average change in pupil size across observers as a function of time from slit onset per observed pupil size condition in experiment 1. The eye regions presented in the slits were equalized in luminance and contrast. The right plot shows the average and standard error of the change in pupil size across observers, after averaging between 1 and 3 seconds from slit onset, per observed pupil-size condition (small: S; original: O; large: L; n.s.: not significant; * < 0.05).
Figure 4
The top row shows the average change in pupil size across observers as a function of time from face onset per emotional expression condition in experiment 1. The dotted lines around the solid lines indicate standard errors of the mean. The bottom row shows the average and standard error of the change in pupil size across observers, after averaging between 1 and 3 seconds from face onset, per observed pupil-size condition (small: S; original: O; large: L; n.s.: not significant).
Figure 5
Top row shows average change in pupil size across observers as a function of time from observed pupil change onset per pupil condition in experiment 2. Bottom row shows average and standard error of change in pupil size across observers, after averaging between 1.0 and 2.5s from observed pupil change onset, per observed pupil-size condition (decreasing: D; static: S; increasing: I; n.s.: not significant; ** < 0.01, *** < 0.001). Data were split per luminance-not-equalized (1st and 2nd columns) and luminance-equalized (3rd and 4th columns) pupils, and in-group (1st and 3rd) and out-group faces (2nd and 4th).
Table 3
Four-way ANOVA on observer’s average pupil size with all main-effects and relevant interactions between the factors group, luminance correction, emotion, and pupil size condition in experiment 2.
| Factor | F-value | p-value | BF |
|---|---|---|---|
| Pupil size | 0.97 | 0.383 | 0.012 |
| Group | 12.68 | <0.001 | >100 |
| Luminance eq. | 0.01 | 0.921 | 0.056 |
| Emotion | 7.99 | 0.006 | 2.114 |
| Pupil size * Luminance eq. | 21.58 | <0.001 | 14.004 |
Table 4
Means, confidence intervals, and post-hoc t-test comparisons across pupil size conditions per equalization and group condition in experiment 2.
| Condition | Compared conditions | Mean difference | Confidence interval | t-value | p-value | Cohen’s D | BF | |
|---|---|---|---|---|---|---|---|---|
| Not eq./In-group | Sma. | Ori. | –0.15 | –0.25/–0.05 | 2.89 | 0.005 | 0.402 | 665 |
| Ori. | Lar. | –0.04 | –0.14/–0.06 | 0.76 | 0.453 | 0.098 | ||
| Sma. | Lar. | –0.18 | –0.26/–0.10 | 4.50 | <0.001 | 0.554 | ||
| Equalized/In-group | Sma. | Ori. | 0.05 | –0.05/0.15 | 1.05 | 0.297 | 0.141 | 0.197 |
| Ori. | Lar. | –0.01 | –0.12/0.10 | 0.16 | 0.872 | 0.024 | ||
| Sma. | Lar. | 0.04 | –0.05/0.14 | 0.89 | 0.379 | 0.109 | ||
| Not eq./Out-group | Sma. | Ori. | –0.04 | –0.14/0.05 | 0.94 | 0.352 | 0.128 | 0.259 |
| Ori. | Lar. | –0.01 | –0.12/0.10 | 0.24 | 0.812 | 0.036 | ||
| Sma. | Lar. | –0.06 | –0.16/0.04 | 1.17 | 0.247 | 0.144 | ||
| Equalized/Out-group | Sma. | Ori. | 0.04 | –0.05/0.15 | 0.89 | 0.378 | 0.124 | 0.717 |
| Ori. | Lar. | 0.05 | –0.05/0.15 | 1.02 | 0.309 | 0.137 | ||
| Sma. | Lar. | 0.10 | –0.01/0.20 | 1.89 | 0.063 | 0.232 | ||