Figure 8. Influence of respiration on the pupil signal in one example subject.
(a) The pupil size (black trace) and the pressure in the waist cuff (gray trace) were measured concurrently. (b) ARX analysis highlighted a significant influence of the respiration signal on the pupil size. The shaded area indicates the 99% confidence interval of the impulse response. (c) The percentage of variance explained depended on the time horizon - i.e. how far ahead in time was the model prediction – but topped around 3%. (d) The effect of respiration was then removed from the pupil trace, to illustrate the capacity of this approach to clean the signal from unwanted influences.