Development of the Linguistic Evaluation of Prefrontal Synthesis (LEPS) test for children with language delay

Abstract

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 visually synthesize the cat and the mat together in front of the minds eye to appreciate their relations. This type of voluntary imagination, which involves juxtaposition of mental objects is conducted by the prefrontal cortex and is therefore called Prefrontal Synthesis (PFS). While PFS is essential for understanding of complex language, its 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 hundreds of words but never acquire PFS. In these individuals, common tests of intelligence based on vocabulary assessment may miss the profound deficit in PFS. Accordingly, we developed a 5-minute test specific for PFS - Linguistic Evaluation of Prefrontal Synthesis or LEPS - and administered it to 50 neurotypical children, age 2 to 7 years (4.1{+/-}1.3) and to 23 individuals with impairments, age 8-21 years (16.4{+/-}3.0). All neurotypical children older than 4 years received the LEPS score 7/10 or greater indicating good PFS ability. Among individuals with impairments only 9 of 23 (39%) received the LEPS score 7/10 or greater. LEPS score was 90% correct in predicting high-functioning vs. low-functioning class assignment in individuals with autism, while full-scale IQ score was only 50% correct.