Spatial interference among moving targets.

Abstract

Peripheral vision for static form is limited both by reduced spatial acuity and by interference among adjacent features ('crowding'). However, the visibility of acuity-corrected image motion is relatively constant across the visual field. We measured whether spatial interference among nearby moving elements is similarly invariant of retinal eccentricity and assessed if motion integration could account for any observed sensitivity loss. We report that sensitivity to the direction of motion of a central target-highly visible in isolation-was strongly impaired by four drifting flanking elements. The extent of spatial interference increased with eccentricity. Random-direction flanks and flanks whose directions formed global patterns of rotation or expansion were more disruptive than flanks forming global patterns of translation, regardless of the relative direction of the target element. Spatial interference was low-pass tuned for spatial frequency and broadly tuned for temporal frequency. We show that these results challenge the generality of models of spatial interference that are based on retinal image quality, masking, confusions between target and flanks, attentional resolution limits or (simple) "averaging" of element parameters. Instead, the results suggest that spatial interference is a consequence of the integration of meaningful image structure within large receptive fields. The underlying connectivity of this integration favours low spatial frequency structure but is broadly tuned for speed.