Functional but not obligatory link between microsaccades and neural modulation by covert spatial attention

Covert visual spatial attention modulates neural activity and biases the direction of small eye movements, known as microsaccades. Here, the authors show that these two markers co-vary, but that microsaccades are not necessary for neural modulation by attention to occur. Covert spatial attention is associated with spatial modulation of neural activity as well as with directional biases in fixational eye movements known as microsaccades. We studied how these two 'fingerprints' of attention are interrelated in humans. We investigated spatial modulation of 8-12 Hz EEG alpha activity and microsaccades when attention is directed internally within the spatial layout of visual working memory. Consistent with a common origin, spatial modulations of alpha activity and microsaccades co-vary: alpha lateralisation is stronger in trials with microsaccades toward versus away from the memorised location of the to-be-attended item and occurs earlier in trials with earlier microsaccades toward this item. Critically, however, trials without attention-driven microsaccades nevertheless show clear spatial modulation of alpha activity - comparable to trials with attention-driven microsaccades. Thus, directional biases in microsaccades correlate with neural signatures of spatial attention, but they are not necessary for neural modulation by spatial attention to be manifest.

Automated summary

The study found that covert visual spatial attention can modulate neural activity and bias the direction of microsaccades. These two markers co-vary but microsaccades are not necessary for neural modulation by attention to occur.