Spatial attention shapes stimulus-evoked neural activity, boosting response amplitudes of neurons and shifting the size and position of their visual receptive fields. However, relatively little is known about how attention shapes sensory population codes, even though perception ultimately depends on population activity. Here, we measured the electroencephalogram (EEG) in human observers, and isolated stimulus-evoked activity that was phase-locked to the onset of attended and ignored visual stimuli. Using a spatial encoding model, we reconstructed population tuning functions from the topography of evoked activity across the scalp. We found that spatial attention boosted the amplitude of spatially tuned population responses within 100 ms of stimulus onset. Moreover, parametric variation of stimulus contrast revealed that this effect of attention increased with stimulus contrast, suggesting that attention increases the response gain of spatial population codes during the first wave of visual processing.
bioRxiv Subject Collection: Neuroscience