In the present work we focus our attention on the type of understanding which is caused by listening to passages produced by vocal synthesizers, using two different methodologies: multiple choice test (Test 1) and click monitoring task (Test 2). Two texts taken from a published Italian reading comprehension test and pronounced by a human speaker and by the Olivetti PC Vox synthesizer were used. In Test 1, 150 subjects after listen to a passage had to answer ten multiple choice questions. In Test 2, other 50 subjects during the listening of a passage had to recognize some computer generated clicks distributed in the passage. The results of Test 1 show no statistically significant differences in performance between subjects who listened to natural passages and those who listened synthetic passages. The results of Test 2 show that click monitoring responses were faster for clicks in natural speech compared to those in synthetic speech.