Effects of Preparatory Attention to Nonspatial Features in the Visual Cortex

Selective attention boosts neural responses to visual stimuli at attended locations or with attended features. Studies have also demonstrated attention-related changes in neural activity in regions coding the attended location or feature before the onset of visual stimuli. Several theories propose that these preparatory "baseline shifts" reflect top-down attentional biasing and may themselves modulate stimulus-driven neural responses. While location-specific preparatory activity is observed consistently for spatial attention, the evidence for analogous feature-specific activity during attention to nonspatial features is mixed. In this chapter, we review evidence for feature-specific preparatory attention effects in the sensory cortex and consider the factors that might influence whether they are observed.