Relating microsaccades and EEG-alpha activity during covert spatial attention in visual working memory

Abstract

Covert spatial attention is associated with spatially specific modulation of 8-12 Hz EEG-alpha activity as well as with directional biases in fixational eye-movements known as microsaccades. However, how these two well-established ‘fingerprints’ of covert spatial attention are related remains largely unaddressed. We investigated the link between microsaccades and spatial modulations in alpha activity in humans in a context with no incentive for overt gaze behaviour: when attention is directed internally within the spatial layout of visual working memory. We show that the two signatures are functionally correlated. The spatial modulation of alpha activity is stronger in trials with microsaccades toward vs. away from the to-be-attended visual memory item. Moreover, the alpha modulation occurs earlier in trials with earlier microsaccades toward the memorised location of the cued memory item. At the same time, however, in trials in which we did not detect any attention-driven microsaccade, we nevertheless observed clear spatial modulation of alpha activity. Taken together, these results suggest that directional biases in microsaccades are functionally correlated to alpha signatures of internally directed spatial attention, but they are not necessary for alpha modulations by covert spatial attention to occur.