Exploring Attention in Depth: Event-Related and Steady-State Visual Evoked Potentials During Attentional Shifts Between Depth Planes in a Novel Stimulation Setup.

Visuo-spatial attention acts as a filter for the flood of visual information. Until recently, experimental research in this area focused on neural dynamics of shifting attention in 2D space, leaving attentional shifts in depth less explored. In this study, twenty-three participants were cued to attend to one of two overlapping random-dot kinematograms (RDKs) in different stereoscopic depths in a novel experimental setup. These RDKs flickered at two different frequencies to evoke Steady-State Visual Evoked Potentials (SSVEPs), a neural signature of early visual stimulus processing. Subjects were instructed to detect coherent motion events in the to-be-attended-to plane/RDK. Behavioral data showed that subjects were able to perform the task and selectively respond to events at the cued depth. Event-Related Potentials (ERPs) elicited by these events-namely the Selection Negativity (SN) and the P3b-showed greater amplitudes for coherent motion events in the to-be-attended-to compared to the to-be-ignored plane/RDK, indicating that attention was shifted accordingly. Although our new experimental setting reliably evoked SSVEPs, SSVEP amplitude time courses did not differ between the to-be-attended-to and to-be-ignored stimuli. These results suggest that early visual areas may not optimally represent depth-selective attention, which might rely more on higher processing stages, as suggested by the ERP results.