RESUMO
In order to grasp the difference between "the cat on the mat" and "the mat on the cat," understanding the words and the grammar is not enough. Rather it is essential to visualize the cat and the mat together to appreciate their relations. This type of imagination, which involves juxtaposition of mental objects is conducted by the prefrontal cortex and is therefore called Prefrontal Synthesis (PFS). PFS acquisition has a strong experience-dependent critical period putting children with language delay in danger of never acquiring PFS and, consequently, not mastering complex language comprehension. In typical children, the timeline of PFS acquisition correlates with vocabulary expansion. Conversely, atypically developing children may learn many words but never acquire PFS. In these individuals, intelligence tests based on vocabulary assessment may miss the profound deficit in PFS. Accordingly, we developed a test specific for PFS - Linguistic Evaluation of Prefrontal Synthesis or LEPS - and administered it to 50 neurotypical children, age 4.1 ± 1.3 years and to 23 individuals with impairments, age 16.4 ± 3.0 years. All neurotypical children older than 4 years received the LEPS score 7/10 or greater indicating good PFS ability. Among individuals with impairments only 39% received the LEPS score 7/10 or greater. LEPS was 90% correct in predicting high-functioning vs. low-functioning class assignment in individuals with impairments.