Crowding is reduced by onset transients in the target object (but not in the flankers) John A. Greenwood # $ Experimental Psychology, University College London, London, UK Laboratoire Psychologie de la Perception, Universit ´ e Paris Descartes, CNRS UMR 8242, Paris, France Bilge Sayim # $ Laboratoire Psychologie de la Perception, Universit ´ e Paris Descartes, CNRS UMR 8242, Paris, France Laboratory of Experimental Psychology, University of Leuven, Leuven, Belgium Patrick Cavanagh # $ Laboratoire Psychologie de la Perception, Universit ´ e Paris Descartes, CNRS UMR 8242, Paris, France In peripheral vision, objects that are visible in isolation become difficult to identify in clutter. This crowding effect is typically strong when objects are similar in a given dimension (e.g., color) and weak when they differ. Here we examine the selectivity of crowding for temporal differences—namely, the transient signals associated with object onsets and offsets. Observers judged the orientation of a peripheral Gabor target surrounded by four flankers. Midway through each trial, selected elements ‘‘blinked’’ off and on again. Performance was poor (crowding was strong) when all Gabors blinked simultaneously or when only the flankers blinked. In contrast, performance improved dramatically when the target alone blinked despite the continued presence of the flankers. This asymmetric release from crowding occurs across a range of blink durations and target–flanker separations. A similar release was found when the target onset was delayed relative to the flanker onsets, though varying the target offset had little effect. This suggests that blinks (composed of offset and onset events) reduce crowding specifically because they separate target and flanker onsets. Finally, with luminance pedestals added to the Gabors, crowding was reduced by blinks in the target pedestal only when the target Gabor was present; pedestal blinks before/after the stimulus Gabors (as precues/postcues) had no effect. That is, transients do not simply cue the target location. The asymmetry of this effect (reduced crowding with target transients, no effect with flanker transients) also precludes explanations based on similarity or grouping. We attribute our findings to the isolation of the target in transient (vs. sustained) visual channels. Introduction Although objects in our peripheral vision can be scaled to become visible in isolation, these same objects are often difficult to recognize in clutter. We refer to this as crowding (Bouma, 1970; Pelli, Palomares, & Majaj, 2004; Levi, 2008). Crowding is typically stronger in peripheral vision than in the fovea, though it is elevated in foveal vision during development (Atkin- son, Anker, Evans, & McIntyre, 1987; Jeon, Hamid, Maurer, & Lewis, 2010) and particularly so in cases of strabismic amblyopia (Flom, Weymouth, & Kahne- man, 1963; Levi & Klein, 1985). The disruption to visual recognition in these cases provides a clear motivation to understand how to reduce crowding–or avoid it altogether. However, although much is known about the selectivity of crowding with static stimuli, the dynamic properties of crowding are far less understood. Because the visual world is ever-changing, we sought to examine whether crowding is modulated by the transient signals that occur when objects appear and disappear. Citation: Greenwood, J. A., Sayim, B., & Cavanagh, P. (2014). Crowding is reduced by onset transients in the target object (but not in the flankers). Journal of Vision, 14(6):2, 1–21, http://www.journalofvision.org/content/14/6/2, doi:10.1167/14.6.2. Journal of Vision (2014) 14(6):2, 1–21 1 http://www.journalofvision.org/content/14/6/2 doi: 10.1167/14.6.2 ISSN 1534-7362 Ó 2014 ARVO Received October 18, 2013; published August 1, 2014