Automatic discrimination of digits and letters in first graders and adults: an EEG Fast Periodic Visual Stimulation study.

Both letters and digits are arbitrary visual shapes that are distinguished into categories only after cultural acquisition. The observation that digits are easier to identify than letters has been repeatedly reported in the literature (Shubert, 2017). In the present study, we used a Fast Periodic Visual Stimulation approach with EEG recordings to assess the automatic discrimination of letters and digits from each other in 1st grade children (N=17) and in adults (N=18). Participants viewed 40 sec sequences (3 repetitions per condition) of frequent stimuli (letters or digits) at a fast periodic rate (adults: 10Hz, children: 6Hz), in which rare stimuli (the other category of alphanumeric symbols) were periodically inserted (every five items, e.g., adults: at 2Hz, children: at 1.2Hz). Results showed discrimination responses in both groups in posterior occipito-temporal regions with clear changes in lateralization patterns. In children, stimuli contained only single elements. Responses were right-lateralized for digits among letters, and revealed a trend for left-lateralization for letters among digits. In adults, when stimuli contained only 1 character, both letters and digits gave rise to responses in the RH. However, when strings of characters were presented, then letters were discriminated from digits in the LH. These findings show a developmental pattern where single elements in children seem to be processed like strings of elements in adults.