Andreasen N C, Alpert M, Martz M J
Arch Gen Psychiatry. 1981 Mar;38(3):281-5. doi: 10.1001/archpsyc.1981.01780280049005.
Acoustic analysis of voice patterns is an objective means of evaluating flatness of affect. Thirty-one patients defined as having flat affect by a reliable rating scale were compared with 30 patients who were not flat. The hypothesis that flat patients display monotonic speech was confirmed, for these patients showed less variance in both the amplitude and frequency of their speech than the nonflat patients.
