Spatial visual attention prioritizes specific locations while disregarding others. The location of spatial attention can be deployed without overt movements (covertly). Spatial dynamics of covert attention is exceptionally difficult to measure due to its hidden nature. One way to implicitly index the location of covert attention is via pupillary light responses (PLR), as the strength of PLR is modulated by where attention is allocated. However, this method has so-far necessitated simplistic stimuli. Here we report on a novel pupillometric method that allows to track covert attention even with highly complex stimuli. Participants (n = 36) watched movie clips while they either passively viewed the movie, or they top-down shifted covert attention to targets in the left, right, or both sides of the visual field. Using a recent toolbox (Open-DPSM), we evaluated whether luminance changes in regions presumably receiving more attention contribute more strongly to the pupillary responses – and thereby reveal covert attention. Three independent and established effects of covert attention on pupil responses were found: (1) a bottom-up effect suggesting more attention drawn to more dynamic regions in the movie, (2) a top-down effect suggesting more attention towards the instructed direction, and (3) an overall tendency to attend the left side (i.e., pseudoneglect). These findings show that pupil responses can physiologically index covert attention with our approach, even in highly dynamic and complex environments. We see considerable potential in measuring covert attention with our method in many real-life scenarios that were impossible to study before.

Touch is important for many aspects of our daily activities. One of the most important tactile characteristics is its perceived intensity. However, quantifying the intensity of perceived tactile stimulation beyond subjective self-reports remains challenging. Here, we show that pupil responses can objectively index the intensity of tactile stimulation in the absence of overt participant responses. In Experiment 1 (n=32), we stimulated three reportedly differentially sensitive body locations (finger, forearm, calf) with a single tap of a tactor while tracking pupil responses. Tactile stimulation resulted in greater pupil dilation than a baseline without stimulation. Furthermore, pupils dilated more for the more sensitive location (finger) than for the less sensitive locations (forearm, calf). In Experiment 2 (n=20) we extended these findings by manipulating the intensity of the stimulation with three different intensities, here a short vibration, always at the little finger. Again, pupils dilated more when being stimulated at higher intensities as compared to lower intensities. In summary, pupils dilated more for more sensitive parts of the body at constant stimulation intensity and for more intense stimulation at constant location. Taken together, the results show that the intensity of perceived tactile stimulation can be objectively measured with pupil responses – and that such responses are a versatile marker for touch research. Our findings may pave the way for previously impossible objective tests of tactile sensitivity, for example in minimally conscious state patients.