Attentional deployment to Space and Features: Separate and Together

Top-down visual attention selectively filters sensory input so relevant information receives preferential processing. Feature-based attention (FBA) enhances the representation of attended low-level features, while space-based attention (SBA) enhances information at attended location(s). Both selection mechanisms operate upon common neuronal populations within visual cortex, but how their unique influences combine to facilitate behavior remains a focus point of study. Here, we utilized an arrow precue containing color and spatial information that together predicted a relevant object (unfilled square) 70% of the time (fully valid condition). For the remaining 30% of trials, the relevant square either: occupied the cued location but was depicted in an uncued color (space-valid, feature-invalid; 10%), was in the cued color but an uncued location (feature-valid, space-invalid; 10%), or mismatched the cued location and cued color (fully invalid; 10%). Importantly, the subjects' task— to report the location of a gap on the square—was completely orthogonal to all precued information. Thus, we could investigate whether FBA and SBA are deployed independently or jointly in a discrimination task that does not favor one mechanism over the other. Additionally, we employed a variable target onset time of 500, 1000 or 1500 ms to coarsely explore any temporal differences and/or interplays between mechanisms. Notably, discrimination performance should be maximized if FBA and SBA are simultaneously and independently deployed. Instead, at 500 ms, FBA and SBA were deployed conjointly: Enhancement of the cued feature was restricted to the cued location. By 1500 ms, subjects relied only on the spatial cue. In another study, where subjects viewed only a feature or spatial cue, FBA deployment was similarly early and transient, while SBA was deployed later and sustained longer. The temporal differences between mechanisms when tested separately suggest independence, while the combinatorial deployment indicates limits to this independence, likely due to a common resource.