Development of Electrophysiological Correlates of Face/non-face Distinction in Children with Late Sight Onset

We have had an opportunity to examine the development of face processing in children who underwent surgeries to treat congenital cataracts several years after birth. We have documented the progressive manifestation of the face/non-face classification ability in such children in our earlier behavioral work. Here, we report our studies on the development of EEG-based neural markers associated with the face/non-face distinction. As part of Project Prakash, a humanitarian and scientific effort focused on treatment and study of early blind children, we had an opportunity to work with 7 children who had dense bilateral congenital cataracts and underwent surgeries around adolescence. Our EEG study presented 100 images each of faces and non-faces, in random order. The stimulus display time was set to 300 ms and the inter-stimulus interval ranged between 1-1.5s. We used a gel based 64 channel EEG system. Recordings were collected longitudinally at 4 time points, viz. before treatment, immediately after treatment, 1 month and 3 months after the treatment. We calculated event related potentials and tracked the well-known N170 ERP component, known to be associated with structural encoding of faces. Our results reveal that the EEG signals evoked by faces and non-faces immediately after the treatment are statistically indistinguishable. Interestingly, however, face-specific N170 responses emerges within a few months of treatment, qualitatively mirroring the behavioral results we have observed previously. Furthermore, the location of the N170 in the Prakash children is consistent with its location in the typically sighted. We conclude that face-specific neural processing can be instantiated even after several years of early onset visual deprivation, and such processing in the late-sighted shows spatio-temporal characteristics similar to those in normally sighted individuals.