Zooming in and out: Selective attention modulates color signals in early visual cortex for narrow and broad ranges of task-relevant features.

Research on feature-based attention has shown that selecting a specific visual feature (e.g., the color red) results in enhanced processing in early visual cortex, providing the neural basis for the efficient identification of relevant features in many everyday tasks. However, many situations require the selection of entire feature ranges instead of just a single feature value, and recent accounts have proposed that broadly tuned attentional templates are often critical for guiding selection in cluttered visual scenes. To assess the neural implementation of such broad tuning of feature-based attention, we here recorded frequency-tagged potentials in human observers (male and female) while participants attended to narrow or broad ranges of colors of spatially intermingled dot fields. Our results show clear increases in the signal strength for the attended colors relative to unattended colors for both narrow and broad color ranges, though this increase was reduced for the broad-range condition, suggesting that limits in the breadth of attentional tuning arise at early processing stages. Overall, the present findings indicate that feature-selective attention can amplify multiple contiguous color values in early visual cortex, shedding light onto the neural mechanisms underlying broad search templates. More generally, they illustrate how feature-based attention can dynamically 'zoom in' and 'zoom out' in feature space, mirroring models of spatial attention.Significance statement Many daily situations require the human brain to focus attention to entire sets of feature values, for example when looking for apples in the supermarket which may range from red to yellow to green. How is such broad selection of perceptually contiguous features accomplished? Using electroencephalography, we directly measured early visual processing while participants attended to different color ranges. Our results demonstrate that processing of entire sets of colors is increased in early visual cortex, though the magnitude of this enhancement is modulated by the selected range. This result is important for our understanding of how attention is allocated in complex visual scenes in which relevant inputs are often variable and not defined by a single feature value.