Pupil size is sensitive to dynamic change in scene layout properties

Abstract

Previously we observed that pupil size is modulated by scene layout properties: smaller when viewing far or open scenes. Here we investigate whether changing direction of these properties, in addition to their static value, will also affect pupil size, by comparing pupillary response to otherwise identical scenes after exposure to scenes of different depths. 10 naive volunteers were instructed to free-view a series of 479 color video clips (mean duration ~8.57 s) in random order, while binocular pupil size was recorded using Eyelink 1000 eyetracker. All clips were extracted from documentary movies depicting natural or man-made sceneries, and were preprocessed to have roughly matched mean luminance and RMS contrast in each frame. Dominant depth of the scene in the clips was continuously rated by another group of 10 observers in separate sessions. Trials were sorted according to whether depth rating of preceding clip (adaptor) was farther, similar (served as baseline), or nearer compared with current clip (probe). Event-related pupil response time-locked to video onset was constructed for clips with at least one trial in all three conditions, and averaged across clips. When adaptor was farther, pupil size was significantly larger than baseline condition starting from as early as 280 ms, as if the probe was perceived nearer. The opposite was true when adapted to nearer scenes. Notably, larger difference in depth between adaptor and probe was significantly correlated with greater change in pupil size. Near reflex couldn't explain the result because it would predict opposite trend. In conclusion, the result suggests that pupil response is not only modulated by static value of scene layout properties, but also sensitive to their dynamic changes, probably due to high-level aftereffect in scene perception. Meeting abstract presented at VSS 2017