Flexible allocation of feature-based attention to narrow and broad ranges of colors as assessed by steady-state visual evoked potentials

We can allocate our attentional resources to select a specific visual feature, such as the color red, and prioritize its processing. Can we also tune our attention to multiple feature values at the same time? This would be useful given that objects in the environment are often variable and include ranges of feature values (e.g., apples are not just a singular red, but often a mix of reddish colors). The current study examines how participants select narrow and broad ranges of colors, and how this selection affects early visual-cortical processing using EEG. Participants (N=24) continuously attended a set of target dots among distractor dots to detect a brief interval of coherent motion that occurred in a subset of targets (on 50% of trials) while ignoring distractors. The range of target colors was varied systematically to span narrower or broader parts of a perceptually uniform color wheel (20º vs 60º around a target color center), and the distractor dots were always chosen to be maximally distinct from the targets in that feature space (i.e., 180º away from the target center). To match task difficulty across conditions, motion speed thresholds were obtained separately for each individual and condition. We assessed early visual processing of the color arrays by flickering target and distractor dots at distinct frequencies (7.5 and 8.57 Hz) to elicit separable steady-state-visual evoked potentials (SSVEPs). Our results showed that the SSVEP power measured over the occipital cortex was enhanced for targets relative to distractors across both conditions; interestingly, this enhancement was not modulated by color range, suggesting that attention flexibly and efficiently increased color representations across narrow and broad color ranges at early stages of visual processing. Overall, these results indicate that feature–based attention can be adaptively tuned to varying feature values and enhance their neural processing efficiently.