The effect of luminance gradient induced luminosity and darkness in static and dynamic patterns on pupil diameter

Luminance gradients can determine strong brightness illusions, which, depending on how gradients are organized around a target area (T), may result in brightness enhancement (e.g. glare effect) or brightness depression (i.e. ‘darkness enhancement’). The effects of such illusions on the eye pupil’s response were studied in an experiment with static and dynamic patterns (similar to the standard ‘glare effect’ pattern) by employing a remote eye-tracking device. Control stimuli were patterns in which luminance gradients were rotated 180 with respect to T, determining peripheral brightness effects external to T. Factors were thus Luminosity (bright, dark), Effect (central, peripheral) and Pattern (static, dynamic). Results show a main effect of Luminosity and Pattern, and a significant interaction Luminosity x Effect for both static and dynamic patterns. Summarizing, central bright patterns determined smaller pupils whilst central dark patterns determined larger pupils; the effects for dynamic stimuli were twofold those for static stimuli. Results confirm findings from previous studies with static patterns, while showing that the effect of illusory brightness patterns on pupil diameter extends to illusory darkness patterns and is enhanced by dynamic stimuli