This paper describes a perception experiment which aims at testing the ability of subjects to discriminate prosodic boundaries when provided with fundamental frequency and duration. Their task consists in listening to a high quality speech synthesizer producing nonsense speech that copies the prosodic parameters of a French corpus. Subjects have marked boundary syllables with a device that synchronizes sound and orthographic transcription. Results show that the delexicalization procedure is ecological, and that duration strongly influences the perception of fundamental frequency.