We compare a psycholinguistic approach of mental lexicon organization with a computational approach of implicit lexical organization as found in dictionaries. In this work, we associate dictionaries with 'small world' graphs. This multidisciplinary approach aims at showing that implicit structure of dictionaries, mathematically identified, fits the way young children categorize. These dictionary graphs might therefore be considered as 'cognitive artifacts'. This shows the importance of semantic proximity both in cognitive and computational organization of verbs lexicon.