They were divided into two grade groups: 26 children (14 males) attended the second grade and were 7–8 years old (M = 8;2, range = 7;7–8;8); and 26 children (15 males) attended the fourth grade and were 9–10 years old (M = 10;2, range = 9;8–10;4). Exclusion criteria included bilingualism, known neurological Depsipeptide and psychiatric medical history, developmental learning disorders, and visual or auditory impairment. Children’s participation was conditional upon approval by their head teachers and teachers, and their own willingness to take part in the experiment. They were aware that they could withdraw from the experiment at any time without further consequences. Moreover, all parents provided written informed

consent for their children’s participation in the study, and all data was stored anonymously. Children were tested individually in a quiet room at their school, in a single session of approximately 45 min. During this session, participants performed 4 tasks: (1) The Visual anti-PD-1 antibody Recursion Task (VRT),

designed to assess the ability to represent recursive iterative processes in the visuo-spatial domain (Martins & Fitch, 2012); (2) The Embedded Iteration Task (EIT), designed to test the ability to represent non-recursive iterative processes in the visuo-spatial domain (Martins & Fitch, 2012); (3) The Test for Reception of Grammar (TROG-D), a grammatical comprehension PAK5 task (Bishop, 2003 and Fox, 2007); and (4) The Raven’s Coloured Progressive Matrices (CPM), a non-verbal intelligence task (Raven, Raven, & Court, 2010). The whole testing procedure was divided into two parts, with a break of 5 min in between. The first part included VRT and

EIT, as well as a specific training for these tasks, and the second part included TROG-D and CPM. The order of tasks in the first part was randomized and equally distributed: Within each grade group 13 children started the procedure with VRT and 13 children started the procedure with EIT. The order of tasks in the second part was fixed (TROG-D first and then CPM). Both VRT and EIT were binary forced-choice paradigms, where children were asked to choose between two images. After the completion of the first two tasks, we asked 42 out of 52 children the following question: “How frequently were the two images in the bottom different? (a) Almost never, (b) Sometimes, or (c) Almost always?” We initiated this systematic questioning after the experiment had begun, due to the feedback that we got from some children, reporting perceiving no differences between the choice images. Unfortunately, it was not possible to retrieve the answer from the first 10 children. Test procedure. This task was adapted from the one used in (Martins & Fitch, 2012). In VRT, each trial began with the presentation of three images corresponding to the first three iterations (steps) of a fractal generation.