Results
Figure 4A shows the changes in pupil size relative to baseline over
time, Figure 4B shows the pupil size derivatives (see Supplementary
Figure 5 for plots per participant). First, we found that tactile
stimulation at each of the three stimulation intensities resulted in
larger pupil size derivatives as compared to the no-stimulation
condition (see Supplementary Figure 6 for the statistical comparisons),
replicating the stimulation effect reported in Experiment 1.
We found faster increases in pupil size following high versus low
intensity tactile stimulation, and medium versus low intensity tactile
stimulation. No difference was found between high and medium intensity
stimulation. In Figure 4C, the results of the linear mixed effects model
are plotted, showing the t -values for comparisons between
stimulus intensities over time. The results remained conceptually
unchanged when simple functional t -tests were performed on the
mean traces per condition and participant (Supplementary Figure 7).
Thus, tactile stimulation at higher stimulus intensities resulted in
larger pupil responses as compared to lower stimulus intensities.
The time to maximum pupil response (Figure 4D) did not differ between
the three stimulus intensities, χ2(1998) = 0.58,p = 0.748, indicating that differences in pupil response after
tactile stimulation were not driven by differences in pupil response
latency.