Two experiments, one in the visual domain, one in the auditory domain, aimed to investigate the distribution of spatial attention in the radial plane. In both experiments, participants detected infrequent targets at one of four locations, two in near space, two in far space. In one experimental half, participants were instructed to detect infrequent target stimuli on the left or right in near space. In the remaining experimental half, targets detected targets on the same peripheral planes but in far space. The relevant side (left/right) was indicated by a central cue on a trial-by-trial basis. The cue was followed by either a target stimulus or a nontarget stimulus, presented from one of the four stimulus locations (cued or uncued). The ERPs elicited by the cue stimuli and nontarget stimuli were collected, as well as behavioural measures.
In both modalities, behavioural results showed that participants were successful in efficiently selecting stimuli in one depth plane. It was also the case that shifting attention within far space resulted in similar cue-related lateralised effects as in near space. Unexpectedly, in the visual domain the ERPs elicited by nontarget stimuli suggested that initially stimuli from the unattended depth plane attract attention, as reflected by larger N1 amplitudes in comparison to stimuli presented at the relevant depth. This was true for near and far stimuli. In the auditory domain, attentional modulations were stronger if attention was focussed on near space. In both modalities later attention effects (SN) were consistent with behavioural findings and largest for stimuli at the relevant side and at the relevant depth. These results indicate that attention can selectively be employed to a location in depth in both visual and auditory modalities. However, attention may initially be attracted by irrelevant-depth stimuli.