A functional role for trans-saccadic luminance differences

Abstract

In typical natural environments, the visual system receives different inputs in quick succession as gaze moves around. We examined whether local trans-saccadic differences in luminance, contrast, and orientation influenced perception and target selection in the eye movement system. Observers initially fixated a peripheral position in a preview display that consisted of four patterns. They subsequently made a saccade to the center of the configuration. During the movement, two of the preview patterns were eliminated, and a small change in the luminance contrast of the remaining patterns was introduced. Observers had to make a second saccade to the test patch with the greater luminance contrast relative to the background. During the second fixation, test patterns could be in the same retinotopic location as one of the preview patterns during the initial fixation (a retinotopic match) or at a retinotopic location that was empty during the preview epoch (a retinotopic onset). We consistently found a preference to fixate retinotopic onsets over retinotopically matched patterns, but only when the patterns were defined by a luminance difference. Direct measurement of perceived luminance showed that the visual response to retinotopically matched inputs was attenuated, possibly because of retinotopic adaptation. As a consequence, the visual system responds more strongly to trans-saccadic differences in local luminance. We argue that a trans-saccadic comparison of the local luminance at the same retinotopic location is a simple way of finding high spatial frequency edge information in the visual scene. This information is important for image segmentation and interpretation.