Large differences in target-flanker depth increase crowding-evidence from a multi-depth plane display

Crowding occurs when the presence of nearby features causes highly visible objects to become unrecognizable. Although crowding has implications for many everyday tasks and the tremendous amounts of research reflect its importance, surprisingly little is known about how depth affects crowding. Most available studies show that stereoscopic disparity reduces crowding, indicating that crowding may be relatively unimportant in three-dimensional environments. However, most previous studies tested only small stereoscopic differences in depth in which disparity, defocus blur, and accommodation are inconsistent with the real world. Using a novel multi-depth plane display, this study investigated how large (0.54 - 2.25 diopters), real differences in target-flanker depth, representative of those experienced between many objects in the real world, affect crowding. Contrary to previous work showing small differences in target-flanker depth reduce crowding, the larger depth differences tested in our study instead increased crowding. While this is likely due to increased clutter in areas outside the limits of binocular fusion, analysis of the stimuli’s perceived appearance indicates the increase in crowding occurs even in the absence of reported diplopia. These findings suggest that crowding has a more significant impact on our perception of natural three-dimensional environments than previously estimated with 2D displays.