Attentional guidance by relative features: Behavioral and electrophysiological evidence.

Our ability to select task-relevant information from cluttered visual environments is widely believed to be due to our ability to tune attention to the particular elementary feature values of a sought-after target (e.g., red, orange, yellow). By contrast, recent findings showed that attention is often tuned to feature relationships, that is, features that the target has relative to irrelevant features in the context (e.g., redder, yellower). However, the evidence for such a relational account is so far exclusively based on behavioral measures that do not allow a safe inference about early perceptual processes. The present study provides a critical test of the relational account, by measuring an electrophysiological marker in the EEG of participants (N2pc) in response to briefly presented distractors (cues) that could either match the physical features of the target or its relative features. In a first experiment, the target color and nontarget color were kept constant across trials. In line with a relational account, we found that only cues with the same relative color as the target were attended, regardless of whether the cues had the same physical color as the target. In a second experiment, we demonstrate that attention is biased to the exact target feature value when the target is embedded in a randomly varying context. Taken together, these results provide the first electrophysiological evidence that attention can modulate early perceptual processes differently; in a context-dependent manner versus a context-independent manner, resulting in marked differences in the range of colors that can attract attention.