Amelia H. Harrison¹, Thomas C. Sprague¹; ¹University of California, Santa Barbara

Typically, when spatial attention is directed to multiple locations simultaneously, perceptual sensitivity to stimuli at those locations is reduced relative to attending only a single location (e.g., Ling & Carrasco, 2006; Popovkina et al., 2021). Additionally, neural responses to visual stimuli are generally attenuated under distributed attention compared to focal attention conditions (e.g., McMains & Somers, 2005; Toffanin et al., 2009). However, fMRI data from a previous study in our lab show a different pattern: focal spatial attention enhances the neural representation of a stimulus compared to when the stimulus is ignored, but the degree of enhancement does not decrease as an additional stimulus is attended (Harrison et al., VSS 2024). To resolve the discrepancies between this finding and prior literature, we conducted an EEG experiment in which participants performed a selective attention task modeled after our previous fMRI experiment. fMRI and EEG have been suggested to assay complementary attentional modulations arising from distinct physiological processes (e.g., Itthipuripat et al., 2019), motivating its use for better understanding the neural mechanisms surrounding distributed spatial attention. Participants were cued on each trial to attend to the fixation point, to one cued peripheral location, or to two cued peripheral locations where flickering stimuli (20 and 24 Hz) appeared on every trial. In our pilot dataset, we compared steady-state evoked potential (SSVEP) amplitudes for each stimulus across attentional conditions and found that while attending to a single stimulus increases evoked power, the effects of distributed attention, compared to focal attention, are variable. In line with our prior fMRI results, there is no clear evidence that distributed attention reduces attentional enhancement compared to focal attention. This is consistent with a model where attentional feedback signals enhance sensory responses to a similar degree when attention is focused as when it is distributed.

Acknowledgements: Research supported by a University of California, Santa Barbara Academic Senate Research Grant and an Alfred P Sloan Research Fellowship.