 After further sessions Ildefonso began carrying a list of English words in his pocket that, Schaller noted, he treated with the utmost care.After Ildefonso's breakthrough, Schaller found his learning progress very slow, and she worried that he would be unable to acquire language.She then approached linguist Ursula Bellugi at the Laboratory for Cognitive Neuroscience, where Bellugi specialized in the biological foundation of language, and language acquisition, with specific reference to ASL.