Early automatic and late lateralised top-down mechanisms for 3D perception

Three-dimensional (3D) perception is a fundamental aspect of human vision, yet it is not entirely understood how the visual system uses monocular cues to create 3D objects from two-dimensional (2D) retinal input. Recent evidence suggests that early neural activity for depth perception occurs pre-attentively, whilst later 3D shape processing relies on the deployment of top-down attention. However, whether this later processing shows hemispheric lateralisation has received little attention. We utilised the N2pc component, a well-established marker of visual attention, to measure the neural correlates of attention to 3D shape. We hypothesised that greater attentional resources would be allocated to processing 3D compared to 2D shape, and that this activity would be lateralised to the right hemisphere, consistent with previous notions. As predicted, we found that 3D targets elicited a greater N2pc amplitude than 2D targets, but unexpectedly, this effect was only present over the left hemisphere. We suggest that this left lateralised attentional effect is consistent with suggestions that the left ventral visual pathway is dominant in processing 3D shape. Exploratory analysis also revealed a significant polarity reversal between 2D and 3D targets within the time-window of an early lateralised potential (N1pc), consistent with automatic attentional capture by depth information, even when it was task irrelevant. Taken together, these findings suggest that depth information first captures attention automatically, and that subsequent processing of 3D shape engages left lateralised top-down attentional mechanisms.