Abstract
Visual crowding is the difficulty experienced in identifying a target flanked by other objects within the peripheral visual field. Despite extensive research conducted on this topic, the precise relationship between attention and crowding is still debatable. One perspective suggests that crowding is a bottom-up and pre-attentive process, while another suggests that crowding is top-down and attentional. A third perspective proposes that crowding is a combination of bottom-up and top-down processes. To address this debate, the current study manipulated the attention and distance between targets and flankers, while simultaneously measuring event-related potentials, in human participants. Results indicated that, compared to uncrowded targets, crowded targets elicited more negative frontal N1 and P2 activity and a less negative occipital N1 activity, regardless of whether targets were attended or unattended, and a more positive occipital P2 activity when they were attended. Furthermore, the crowded minus uncrowded difference amplitude was more negative over the frontal region and more positive over the occipital region when the targets were attended, compared to when they were unattended during the N1 and P2 stages. This suggests that crowding, a concept that originates from Gestalt grouping, occurs automatically and can be modulated by attention.
Highlights
The crowding effect is a visual phenomenon in which objects are identified in isolation, but become more difficult to identify when surrounded by other objects in the peripheral visual field (Pelli and Tillman, 2008)
Crowding persists even when people are completely unaware of the flankers, which suggests that conscious awareness and attention are not prerequisites for crowding (Ho and Cheung, 2011)
The present study focused on the temporal dynamic relationship between crowding and attention
Summary
The crowding effect is a visual phenomenon in which objects are identified in isolation, but become more difficult to identify when surrounded by other objects in the peripheral visual field (Pelli and Tillman, 2008). Yong et al (2014) examined the question of why individuals with posterior cortical atrophy (PCA) show excessive crowding in central vision and suggested that crowding in PCA can be regarded as a pre-attentive process that uses averaging to regularize the pathologically noisy representation of letter feature positions. A third perspective suggests that crowding is a combination of bottom-up and top-down processes (i.e., crowding occurs automatically and can be modulated by attention). This perspective comes from the Gestalt grouping hypothesis of crowding. The presentation of an attended visual stimulus (e.g., a crowded or uncrowded target) is followed by zero, one, or two unattended auditory stimuli (e.g., a tone) and a response signal. A significant difference in P2 amplitude between crowded and uncrowded targets, both in the attended and unattended conditions, will be observed, and the crowded minus uncrowded difference amplitude will be modulated by attention
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