Pupillometry analysis
Pupillary changes were first baseline corrected on a trial-by-trial
basis by subtracting the mean change in pupil diameter 1000ms before the
beginning of tactile stimulations. Next, to control for inter-individual
variability, pupil data were Z-scored for each subject across all
conditions (Basile et al., 2021; Rudebeck et al., 2014). In each trial,
missing samples due to blinks or loss of the eye-tracking signal during
the tactile stimulation period were interpolated via spline
interpolation using the nearest valid adjacent samples. Pupil responses
were then averaged across trials for each condition. Based on visual
inspection of the average response profile, the mean change in pupil
diameter was extracted for the time window ranging from 0-4 seconds
after stimulus onset (Figure 2a ). Data were analyzed via a
2-way repeated-measures ANOVA with Touch type (CT-optimal vs.
CT-suboptimal) and Hand type (Human vs. Artificial) as within subject
factors. Post-hoc analyses following significant main effects and
interactions were performed by running two-tailed pairwise t-tests, and
multiple comparisons were corrected by means of false discovery rate
(FDR; Benjamini & Hochberg, 1995). All p values < 0.05 were
considered significant.
To test the hypothesis that CT-optimal_Human touch alone induced a
larger pupil size than CT-optimal_Artificial plus CT-suboptimal_Human
touch, supralinearity was quantified by contrasting, for each
participant, the average pupil size in the CT-optimal_Human condition
against the sum of the average pupil size in the CT-optimal_Artificial
plus CT-suboptimal_Human conditions. The effect of CT-optimal_Human
condition was then compared with the added CT-optimal_Artificial and
CT-suboptimal_Human condition with a paired-sample t test to determine
significance.