Enhancing target processing through mere imbalance in visual stimulation: A new, paradoxical phenomenon in experience driven attention

Learning can shape attention in complex and sometimes counterintuitive ways. Here we report a novel form of implicit learning in visual attention that challenges current models of experience-driven attentional control. Across seven experiments, we demonstrate that mere imbalance in visual stimulation across space - independent of task relevance, awareness and even out of the focus of attention - can induce lasting and selective enhancements in target processing. These effects can be paradoxical and stimulus specific: stimuli initially processed as distractors improve subsequent target processing at implicitly learned locations. This happens without changing attentional capture by distractors presented at the same locations. The phenomenon occurs even under passive viewing conditions and is driven solely by the unequal frequency of visual stimulation across space. Crucially, the effect is distinct from typical selection history modulations of attention, generally affecting both targets and distractors in a consistent manner, which is assumed to reflect changes at the level of priority maps of space. These results suggest that the visual system is able to learn spatial contingencies through diverse mechanisms. They show that attentional systems can encode regularities independently of attentional allocation or task relevance and exploit them in a stimulus-selective manner through a previously undocumented implicit learning mechanism. This has implications for models of selective attention, perceptual learning, habituation and statistical learning.