Visual attention exhibits inherent capacity limits, necessitating selective mechanisms for information prioritization. A longstanding debate concerns regarding whether attention selects spatial locations or integrated objects, and how distractors suppression scales with target proximity. The object-based attention (OBA) literature is divided between theories of automatic spatial diffusion within an object versus a prioritized competition account. Similarly, the distractor distance effect is explained by either increased active suppression (Ambiguity Resolution theory) or passive neural attenuation (Biased Competition theory) at close ranges. This study simultaneously investigated these issues by examining how perceptual grouping and spatial distance interact to influence distractor interference. Thirty-two participants performed a feature search task where they identified a shape-defined target while ignoring a color singleton distractor. Stimuli were grouped using two surrounding arcs, and the distance between the target and distractor was manipulated within or across these groups. Results revealed a significant OBA effect, with faster responses when the target and distractor were within the same group versus different groups. A non-monotonic distance effect was found, with the longest reaction times occurring at the farthest distance, contradicting a simple proximity-based interference model. An interaction trend suggested the spatial distance effect was more pronounced within an object. These findings support an attentional priority account of OBA and are best explained by a suppressive surround mechanism, where attentional enhancement of a target actively inhibits processing in its immediate vicinity, rather than passive neural attenuation. This provides key insights into the spatial distribution of attention within and between objects.

Object-based Attention, Spatial Attention, Distractor Suppression, Visual Search, Distance Effect, Suppressive Surround