This paper focuses on a new speech signal based index ("Inter syllabic Interval": ISI), intended to improve the study of disfluencies produced by the chunking process in subjects performing a SI task (Simultaneous Interpreting, i.e., on line oral translation). The variable is introduced on the basis of a discussion of the main methodological trends in the field, with the aim of improving the quality of the numerical treatments applied to the study of SI. It is argued that because the technical and epistemological limitations of the study of pauses, an index based upon the amplitude peaks in the speech signal should provide more reliable and valid information. An exploratory experiment is carried out on a prototypical sample of 4 subjects, performing SI under several conditions. Results show ISI usefulness in detecting events related to high-level cognitive processes, on the basis of the speech signal.