Abstract
Personally-meaningful visual objects, like our partner’s face, are recognized faster (Ramon et al., 2011; Ramon & Gobbini, 2018) and evoke stronger activity in the brain (Herzmann, et al., 2004, Barense et al., 2011, Taylor et al., 2009; Trinkler et al., 2009, Castello et al. 2017). Activity patterns elicited by personally-meaningful objects also better predict semantic judgements about these objects (Charest et al., 2014). Despite evidence for larger brain activity, the impact of familiarity on the spatio-temporal dynamics of object recognition remains poorly understood. Here we set out to track neural representations of familiar and unfamiliar objects in the human brain as they evolve in space and time. Participants (n=20), saw personally-meaningful and unfamiliar objects matched in category (72 images, including faces, bodies, places, objects and pets) while we recorded electroencephalography (EEG) and functional Magnetic Resonance Imaging (fMRI) (in separate sessions). We constructed representational dissimilarity matrices (RDMs) for each EEG time-point, and for each fMRI voxel independently. We computed the RDMs’ spatio-temporal similarity, combining the precise temporal resolution of EEG with the precise spatial resolution of fMRI (see also Cichy et al., 2014, 2016). We thereby mapped the spatio-temporal trajectories of personally-meaningful and unfamiliar object representations. These followed the typical cascade of visual processes bilaterally from primary visual cortex (V1; ~90ms) through to the ventral and dorsal streams (~130ms). Interestingly, unfamiliar representations reached V1 around 20ms later (~110ms). The cascade of neural representations for personally-meaningful objects rapidly involved additional regions in the MTL (~130ms), and dorsomedial and ventromedial prefrontal cortex (~165ms). Together, these results demonstrate for the first time, when and where prior experience and personal familiarity influence object recognition in the brain. Critically, our results strengthen our understanding of the interactions between the visual sensory system, the medial temporal lobes, and the prefrontal cortex in recognising visual objects.
Acknowledgement: European Research Council - START (759432)