Allocation of spatial attention in human visual cortex as a function of endogenous cue validity.

Several areas of visual cortex contain retinotopic maps of the visual field, and neuroimaging studies have shown that covert attentional guidance will result in increases of activity within the regions representing attended locations. However, little research has been done to directly compare neural activity for different types of attentional cues. Here, we used fMRI to investigate how retinotopically-specific cortical activity would be modulated depending on whether we provided deterministic or probabilistic spatial information. On each trial, a four-item memory array was presented and participants' memory for one of the items would later be probed. Critically, trials began with a foveally-presented endogenous cue that was either 100% valid (deterministic runs), 70% valid (probabilistic runs), or neutral. By dividing visual cortex into quadrant-specific regions of interest (qROIs), we could examine how attention was spatially distributed across the visual field within each trial, depending on cue type and delay. During the anticipatory period prior to the memory array, we found increased activation at the cued location compared to noncued locations, with surprisingly comparable levels of facilitation for both deterministic and probabilistic cues. However, we found significantly greater facilitation on deterministic relative to probabilistic trials following the onset of the memory array, with only deterministic cue-related facilitation persisting through the presentation of the probe. These findings reveal how cue validity can drive differential allocations of neural resources over time across cued and noncued locations, and that the allocation of attention should not be assumed to invariably scale alongside the validity of a cue.