There is now a growing body of evidence that the visual system can, under some conditions, make ultra-rapid image classification judgements within around 100-150ms of stimulus onset (e.g., Thorpe et al., 1996, Nature). However, there have been relatively few studies investigating the temporal dynamics of three-dimensional (3D) object recognition, and shape recovery during visual perception – and most previous work has been restricted to studies based on two-dimensional (2D) stimulus displays ignoring potential effects of stereo disparity on the time course of shape processing. We investigated this issue using high-density (256-channel) EEG to record the temporal dynamics of object recognition to novel, multi-part, objects under conditions of mono- and stereo visual presentation. On each trial participants made shape equivalence ('Same'/'Different') judgements to two briefly presented images of novel objects. There were two blocks each of mono- and stereo trials. There were no differences between conditions on the P1 component, but differences between 2D and 3D stimuli arose at the N1, exhibiting a greater negativity over posterior occipito-temporal leads and a stronger positivity over anterior electrodes at around 170ms for 3D views. The same vs. different shape contrast produced ERP modulations during the N2, between 250ms-330ms. A topographic segmentation analysis suggested that 2D and 3D views differed in the intensity of the N1 map, while same vs. different shape stimuli produced distinct N2 map configurations that emerged independently of depth. These results show that stereo disparity modulates the time course of recognition early in the course of visual processing by enhancing the response at around 170ms. The increase in N1 could reflect the accumulation of visual information that allows shape integration to occur more efficiently during the N2 without necessarily modulating the timing of shape recognition per se.
Meeting abstract presented at VSS 2014