Abstract
Face identity recognition in humans is supported by specialized neural processes whose function is substantially impaired when simply turning a face upside-down: the Face Inversion Effect (FIE) (Yin, 1969, https://doi.org/10.1037/h0027474). Inverted faces provide a strong test for whether experience in adulthood can influence face-specific processes because they contain the same visual information as upright faces for which we already have saturated experience, and inverted faces disrupt the biological constraints present at birth for preferential looking (i.e., fewer features in the bottom part than the top part of the stimulus). However, currently, little is known about the plasticity of the neural processes involved in this FIE at adulthood. Here we investigate if extensive training (2 weeks,~15 hr) in young adults discriminating a large set of unfamiliar inverted faces can reduce the FIE for a set of entirely novel faces. 28 adult observers were trained to individuate 30 inverted face identities presented under different depth-rotated views. Following training, we replicate previous behavioral reports of a significant reduction in the behavioral FIE as measured with a challenging four-alternative delayed-match-to-sample task for individual faces across depth-rotated views (Laguesse et al., 2012, https://pubmed.ncbi.nlm.nih.gov/23019119/). Most importantly, using EEG together with a validated frequency tagging approach to isolate face individuation neural responses (Rossion et al., 2020, https://onlinelibrary.wiley.com/doi/10.1111/ejn.14865), we observe a reduction in the neural FIE at the expected occipito-temporal channels. Moreover, the reduction of the neural FIE correlates with the reduction of the behavioral FIE at the individual participant level (r=0.46). The reduction in the neural FIE is not observed in a concurrently frequency tagged control signal that peaks at the more posterior medial occipital channels and reflect general visual responses. Overall, we provide novel evidence suggesting a substantial degree of plasticity in face-specific processes that are key for face identity recognition in the adult human brain.
